warman multi-stage pumping systems jun97

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ISSUED: JUNE 1996

Copyright © WARMAN INTERNATIONAL LTD.

WARMAN INTERNATIONAL LTD

WARMAN PUMPS

ASSEMBLY AND MAINTENANCEINSTRUCTIONS

SUPPLEMENT ‘M6’

Warman International Ltd. is the owner of the Copyright subsisting in this Manual.

The Manual may not be reproduced or copied in whole or in part in any form or by

any means without the prior consent in writing of Warman International Ltd.



MANUAL SUPPLEMENT ‘M6’ ISSUED: JUNE 1996

Copyright © WARMAN INTERNATIONAL LTD

WARNINGS

WARMAN PUMPS - ASSEMBLY AND MAINTENANCE

INSTRUCTION MANUALS AND SUPPLEMENTSIMPORTANT SAFETY INFORMATION

•

The WARMAN PUMP is both a PRESSURE VESSEL and a piece of ROTATING

EQUIPMENT. All standard safety precautions for such equipment should be followed

before and during installation, operation and maintenance.

•

For AUXILIARY EQUIPMENT (motors, belt drives, couplings, gear reducers, variablespeed drives, etc.) standard safety precautions should be followed and appropriate

instruction manuals consulted before and during installation, operation and maintenance.

•

DRIVER ROTATION MUST BE CHECKED before belts or couplings are connected.

Personnel injury and damage could result from operating the pump in the wrong

direction.

•

DO NOT OPERATE THE PUMP AT LOW OR ZERO FLOW CONDITIONS FOR

PROLONGED PERIODS, OR UNDER ANY CIRCUMSTANCES THAT COULD

CAUSE THE PUMPING LIQUID TO VAPORISE. Personnel injury and equipment

damage could result from the pressure created.

•

DO NOT APPLY HEAT TO IMPELLER BOSS OR NOSE in an effort to loosen the

impeller thread prior to impeller removal. Personnel injury and equipment damage could

result from the impeller shattering or exploding when the heat is applied.

•

DO NOT FEED VERY HOT OR VERY COLD LIQUID into a pump which is atambient temperature. Thermal shock may cause the pump casing to crack.

•

FOR THE SAFETY OF OPERATING PERSONNEL, please note that the

information supplied in this Manual only applies to the fitting of genuine Warman parts

and Warman recommended bearings to Warman pumps.

•

Tapped Holes (for Eye Bolts) and Lugs (for Shackles) on Warman Parts are for lifting

Individual Parts Only.





ISSUED: JUNE 1996

LAST ISSUE: JULY 1993

WARMAN PUMPS

ASSEMBLY AND MAINTENANCE INSTRUCTIONSSUPPLEMENT ‘M6’

WARMAN MULTI-STAGE PUMPING SYSTEMS

CONTENT

WARNINGS

CONTENT

INTRODUCTION .......................................................................................................... 1

Multi-Stage (Series) Pumping Explained Figures 1, 2 and 3 ......................................... 1

SINGLE PUMP .................................................................................................................... 2

TWO STAGE PUMP UNIT .................................................................................................. 2

FOUR STAGE PUMP UNIT ................................................................................................ 3

MULTI-STAGE PUMPING AND PUMP STATIONS ........................................................... 4

Pumps Spaced Along The Line ..................................................................................... 5

Advantages And Disadvantages Of Multi-Stage Pump Units Versus Pumps Spaced AtIntervals Along The Pipeline ......................................................................................... 5

Selection Of Pump Liners And Materials ....................................................................... 6

Selection Of Pump Bearing Frame And Lubrication ...................................................... 7Multi-Stage Pumps Used As Turbines........................................................................... 8

GENERAL MULTI-STAGE SYSTEM LAYOUT ............................................................. 8

Pump Stage Layout And Controls - Figure 4 ................................................................. 9

Interstage Piping - Figure 5 ......................................................................................... 10

Pump Sealing ............................................................................................................. 12

PUMP GLANDS AND OPERATION ................................................................................. 12

GLAND WATER PUMPS .................................................................................................. 15

Stand-By Pumps And Spares...................................................................................... 15

Potential Problems And General Precautions ............................................................. 16

PRESSURE RATINGS - PUMP CASINGS AND PUMP CASING BOLTS ....................... 16

RUBBER LINED PUMPS - VACUUM ............................................................................... 16

VARIABLE SPEED PUMPS .............................................................................................. 17

BEARING SPEEDS ........................................................................................................... 19

REQUIREMENTS FOR THE GLAND WATER SUPPLY AND WATER QUALITY ........... 19

∗ Suspended And Dissolved Solids ................................................................................ 19

∗ Inadequate Or Excessive Gland Water Pressure ........................................................ 20

∗ Inadequate Flow ........................................................................................................... 20

LOW, HIGH FLOW AND WATER HAMMER .................................................................... 20

AVOIDANCE OF IMPELLER LOOSENING - RUNBACK AND REVERSE ROTATION ... 21

∗ Correct Directions of Rotation and Input Torque via Pump Shaft ................................ 21

∗ Impeller Loosening ....................................................................................................... 21





∗ Pump Shut-Down On High Static Discharge Heads .................................................... 22

∗ Effects Of Unrestricted Runback And Reverse Rotation ............................................. 23

∗ Stationary Pump - Forced High Flowrate ..................................................................... 24

∗ Diesel Engine Drives .................................................................................................... 24

System Design - Instrumentation ................................................................................ 24System Design and Schematic Layout- Pipeline and Valves Figure 6 and 7 ............... 27

PIPELINE .......................................................................................................................... 27

VALVING ........................................................................................................................... 27

INTAKE SUMP AND PIPELINE FLUSHING ..................................................................... 28

Variable Speed Pumps and Position ........................................................................... 32

Baseplates and Pipe Anchors ..................................................................................... 32

First Stage Pump ........................................................................................................ 32

System Analysis .......................................................................................................... 33

START-UP PROCEDURES ........................................................................................ 34

Filling The Discharge Pipe .......................................................................................... 34

RECOMMENDED START-UP AND FILLING PROCEDURES ......................................... 34

START-UP AND FILLING WITH UNLIMITED WATER SUPPLY ..................................... 35

STARTING AND FILLING WITH VARIABLE SPEED PUMPS ......................................... 36

Start-Up With Line Full ................................................................................................ 36

SIMPLE SYSTEM (FIGURE 6) START-UP WITH LINE FULL ......................................... 36

CONTROLLED SYSTEM (FIGURE 7): START-UP WITH LINE FULL ............................. 38

Start-Up With Line Empty Figures 8, 9, 10, 11, 12 and 13 .......................................... 40

INTRODUCTION TO START-UP PATHS ......................................................................... 41START-UP PATH .............................................................................................................. 42

PIPELINE PROFILE .......................................................................................................... 43

POWER CONSUMPTION (KW) CURVES ....................................................................... 43

NPSH LIMITATION ........................................................................................................... 44

MULTI-STAGE PUMP H/Q CURVES ............................................................................... 45

VARYING SYSTEM RESISTANCE CURVES................................................................... 46

PLANNING THE START-UP AND FILLING PATH ........................................................... 46

START-UP ON AND FILLING THE PIPELINE WITH SLURRY ....................................... 51

START-UP AND FILLING WITH VARIABLE SPEED DRIVES ......................................... 52

SHUT DOWN PROCEDURES .................................................................................... 52

Standard Shut Down ................................................................................................... 52

SIMPLE SYSTEM (FIGURE 6): STANDARD SHUT-DOWN ............................................ 53

CONTROLLED SYSTEM (FIGURE 7): STANDARD SHUT-DOWN................................. 53

Emergency Shut Down ............................................................................................... 54

SINGLE PUMPS SPACED ALONG THE LINE - OPERATION FIGURES 14, 15, 16

AND 17 ....................................................................................................................... 55

Hopper Fed Boosting Pumps ...................................................................................... 55

Pressure Boosting Pumps ........................................................................................... 56



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MANUAL SUPPLEMENT ‘M6’ ISSUED: JUNE 1996 1


INTRODUCTION

Multi-stage pumping is normally applied when the duty requires a total dynamic head in

excess of the maximum head which can be developed by a single centrifugal slurrypump. This is typically around 80 to 120 m of head depending on the application.

There are two types series pumping arrangements that are possible:-

• Multi-stage pump units and

• Separate pumps, spaced at intervals along the pipeline. This section can be

further subdivided into arrangements which incorporate hopper fed boosting

pumps or pressure boosting pumps.

The advantages and disadvantages of these two pumping arrangements are given in

Filling the Discharge Pipe. These indicate that the multistage system is superior and isthe arrangement that will be concentrated on in this manual.

Warman can assist with system design and depending on the application there are the

AHP and AHPP ranges of high pressure pumps that can be utilised for multistage

applications. Sizes range from 6/4 to 20/18. Pumps can be metal or elastomer lined.

Glands have been developed to operate at high pressure or mechanical seals can be

fitted as required.

The application of centrifugal slurry pumps to multistage pumping is not too different to

that required for a single stage. Additional requirements pertain to the casing and its

pressure rating and to the frame selection to ensure adequate bearing life given thehigher thrust loads involved with multi-staging.

The system design is the other major area for consideration. System fundamentals

including starting and stopping in normal and emergency situations is outlined in the

following sections. Each system is usually somewhat unique, so the outlines and

recommendations below are necessarily generalised. Specific recommendations can be

made by contacting Warman.

Throughout this manual, the term "TRAIN" will be used to mean a set of multi-stage

pumps arranged in series. The pump train is normally housed in a building along with

all the associated power supply, gland water pumps and instrumentation. This will bereferred to as a pumping "STATION".

MULTI-STAGE (SERIES) PUMPING EXPLAINED FIGURES 1, 2 AND 3

Many pumping duties require slurries to be transported over long distances and/or

against very high static discharge heads, i.e. against total heads well in excess of heads

which can be developed by a single centrifugal slurry pump.

Typical examples include many requirements for the pumping of concentrates, tailings,

power station ash, underground fill and Mine Dewatering. The high flowrates required

are commonly beyond the capacities of available positive displacement pumps (PDP’s).

In addition, the overall efficiency, i.e.



__



(Hydraulic (useful) power parted to slurry)

(Total Electrical power input to motors) x 100%

of large centrifugal slurry pump installations competes with PDP’s, essentially due to

the high efficiency of large centrifugal slurry pumps and the higher efficiencies of lower-ratio drives between electric motors and the centrifugal pumps. These very high

total head pump applications can be handled by multi-stage (series) pumping, either (a)

multi-stage pump units or (b) separate pumps spaced at intervals along the pipeline

route.

SINGLE PUMP

Figure 1 represents a single centrifugal pump operating at duty point “A”, and at pump

speed, n1. For the required flowrate of Q1, the pump can develop a head H1 at an

efficiency, em1, and at a power consumed of P1. i.e. Duty Point 'A': Q1 /H1.

Figure 1: Single Pump

TWO STAGE PUMP UNIT

Figure 2 represents two identical pumps, arranged in series so that the entire flow

discharged from the first stage pump is piped under pressure through a short length of

piping, directly to the intake flange of the second stage pump and finally from the

discharge of the second stage pump into the discharge pipeline. If both pumps are

operated at the same speed, n1 and as both are handling the same required flowrate, Q1,

each will develop the same Head, H1, at the same efficiency, em1, and consume the

same power, P1.

The total head developed by the 2 stage pump unit combination = 2 x H 1.

i.e. Duty Point 'B': Q1 /2H1

Accordingly, both pumps will be operating under the same conditions except that the

intake head and the discharge head of the second stage pump will both be higher by the

value of the discharge head of the first stage pump (less small losses in the inter-stage

piping).



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Figure 2: Two Stage Pump Unit

FOUR STAGE PUMP UNIT

Figure 3 represents an arrangement similar to Figure 2 but extended to represent a four

Stage Pump unit where the entire flow passes through all 4 identical pumps prior to

entering the discharge pipeline.

If all 4 pumps are identical and are operated at the same speed n1, and as all arehandling the same flowrate, Q1, each will develop the same head H1, at the same

efficiency em1, and each consume the same power P1.

The total head developed by the 4-stage pump unit combined = H1 + H1 + H1 + H1 = 4

X H1 i.e. Duty Point “C”: Q1 /4H1

Accordingly, all 4 pumps will be operating under the same conditions except that the

intake head and the discharge head of each successive stage will be progressively

higher. Neglecting the small losses in the inter-stage piping and assuming that Hs for

the first stage pump = X (metres) the individual values are:

Stage Intake Head

for Stage (m)

Total Head

Developed by

pump (m)

Power

Consumed by

Each Pump

Discharge

Head for

Stage (m)

1st Stage

2nd Stage

3rd Stage

4th Stage

X

X + H1

X + 2H1

X + 3H1

H1

H1

H1

H1

P1

P1

P1

P1

X + H1

X + 2H1

X + 3H1

X + 4H1

4-Stage Unit: Total Head Developed = 4H1; 4P1 = Total Power Consumed



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If the total head developed by the pump, varies from one pump to another, due to

different speeds or different effects of wear, the total head developed by the multi-stage

unit will be the sum of the individual total heads developed by each of the pumps.

Similarly, the total power consumed will be the sum of the individual powers consumedby each of the pump.

Figure 3: Four Stage Pump Unit

MULTI-STAGE PUMPING AND PUMP STATIONS

This type of arrangement is the one most generally used because of its superior

advantages over pumps spaced along the line. This system consists of pumps arranged

in series in the one pumping station. Each lot of pumps arranged in series is referred to

as a train. The pumping station is generally located at the start of the pipeline. This is

normally at the source of the slurry e.g. at the end of a mineral processing plant where

the tailings need to be transported away to a tailings dam or such.

Warman pumps have been employed on multi-stage pump unit installations of up to 6

and 8 stages in one train. The major limitations to the number of stages possible in a

given multi-stage unit are:-

• Pressure ratings of available high-pressure piping and casing pressure ratings of

pumps.

• Generally, suitable high-pressure piping can be obtained, while Warman pumps

with casing pressure ratings up to approximately 7000 kPa are available.



__



Long pipelines could require the use of more than one station along its length. If two or

more stations are required the same advantages apply over a system which requires

pumps arranged along the pipeline. Systems with one or more stations offer the most

system control.

PUMPS SPACED ALONG THE LINE

Unlike the multi-stage pump train and station located at the start of the pipeline, this

arrangement incorporates pumps spaced along the pipeline. They must be spaced at

intervals at which the head (Hm) from the previous stage is still sufficient to act as feed

to the next stage. For proper system operation, the head into each stage must ensure a

good margin of NPSH available above the NPSH required. Variations and system

excursions or up-sets in system operation must be incorporated into any safety margins.

Pumps can be hopper fed or simply act as pressure boosters.

This arrangement has considerable disadvantages, but might be considered if a

maximum of three of four pumps are required to generate the total head. Other

situations may not allow construction of a pump station or the pipeline may be required

to be extended on a regular basis. In this case, pumps can be added along the line when

and as required. Provided that power and maintenance can readily be supplied, then this

may be the arrangement of choice. The topography of the pipeline route may dictate the

pump spacing.

This type of arrangement is often accomplished by having skid mounted pump units.

They can be electrical or diesel driven. Centrifugal pump seals can avoid the necessity

for supplying gland water to pumps spaced along the line.

ADVANTAGES AND DISADVANTAGES OF MULTI-STAGE PUMP UNITS VERSUS PUMPS

SPACED AT INTERVALS ALONG THE PIPELINE

The advantages and disadvantages of these two types of pumping arrangements are

given in a below. These indicate that the multistage system is superior and is the

arrangement that will be concentrated on in this manual. This comparison is given for

completeness.

MULTI-STAGE PUMP UNITS

Advantages

• Reduced cost for buildings, craneage and other facilities for maintenance, at the

one station.

• Reduced cost for installation and operation of power supply, electrical

equipment, electrical controls and instrumentation at the one station. Minimum

manpower owing to supervision of the operation being required at the one

station only.

• Combined Hm/Q characteristics range required, if required to vary flowrate and

to allow for wear, is usually adequately satisfied by variable speed (V/S) on one

or two stages only.• Poor performance of one pump e.g. if heavily worn, usually does not seriously

affect the operation.



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Disadvantages

• High pressure-rating pipe may be required for at least part of the pumping

system.

• Gland-sealed Warman pumps are required for all stages or for at least thesecond and successive pump stages i.e. gland sealing water supply and controls

are required.

PUMPS SPACED AT INTERVALS ALONG THE LINE

Advantages

• Low pressure, less expensive pumps possibly may be used.

• Low pressure-rating pipelines possibly may be used, e.g. plastics, if hopper-fed

pumps are used at each station. Centrifugally-sealed pumps may be used, at

each station, where pumps are hopper fed.

Disadvantages

• Additional costs for provision of buildings, hoppers, craneage and other

maintenance facilities at each station.

• Additional installation and operating costs for the long distance of and

multiplicity of station power supply and controls.

• Additional cost of multiplicity of variable-speed drives for each pump if speed

control is specified for any necessary variation of Hm/Q characteristics.

• Additional manpower required for supervision or inspection of operation at all

stations.

• Spillage and blockages are likely if pumps are hopper-fed at downstream

stations, due to variations between Hm/Q characteristics of individual pumps.

• Additional costs for transportation of personnel and spare parts between

stations.

• Poor performance of one pump e.g. if heavily worn, may result in spillage and

pipeline blockages.

• Gland-sealing water supply and controls are required at each station if the

Pressure-Boosting arrangement is used.

• Pumps and pipework may be burst or severely damaged by hydraulic shock at

start-up, or by high pressure on shutdown if the pressure-boosting arrangement

is used.

SELECTION OF PUMP LINERS AND MATERIALS

The selection of the type of liners (metal or elastomer) follows the same general

procedures that are used for single stage pumps. Warman high pressure pump Types

AHP and AHPP use the same internal wearing components as the lower pressure AH

range. A full range of metal and elastomer liners can be selected. Metal and elastomer

are fully interchangeable and as well it is possible to use a mixture of materials e.g.

metal impeller and throatbush with elastomer liners. The full range of super thick

elastomer liners, high efficiency impellers etc. are also fully interchangeable with the

standard internals.



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Selection of the material depends upon the characteristics of the slurry being pumped

and its wear characteristics. As well as these considerations, the optimum selection of

materials will also require that the following points be taken into consideration:-

• Pump speed - to minimise the number of pump stages, it is generally requiredthat the maximum head be obtained from each stage i.e. each stage will have to

be operated at the maximum possible speed. For elastomer lined pump the

maximum pump speed may require to be limited to avoid thermal breakdown

in the liners. The material of the impeller will also dictate the maximum speed

due to the impeller strength required to counter centrifugal forces and stresses.

• Drive Type - to reduce the number of items in the drive train of each stage, it is

desirable if pumps can be direct coupled. Some pump stages ought to be

variable speed, so the whole pipeline system can be more readily controlled.

Again, for elastomer lined pumps, the maximum pump speed may be limited to

avoid thermal breakdown in liners. The material of the impeller will also

dictate the maximum speed due to the impeller strength required to counter

centrifugal forces and stresses.

• System Design - During the operation of some systems, the possibility may

arise that the pumps would be subjected to negative internal pressures. In such

cases, it is generally preferred to use metal liners and avoid the possibility of

elastomer liners being collapsed inwards due to the higher external

(atmospheric) pressures.

Warman Engineers can assist with the optimum material selections for each multi-stageapplication.

High pressure pump casings are manufactured from high strength ductile SG irons.

Ribs on the casing provide adequate pressure capability while minimising the casing

deflection.

Pump casings utilise high tensile through bolting. The number of bolts is kept to a

minimum to ease maintenance. Bolts are supplied with a baked on Molybdenum

Disulphide coating for low friction and good corrosion protection. This finish does not

degrade the bolt strength properties.

High tensile bolts and coating are generally best also specified for the rest of the pump

and inter-stage bolting particularly from the corrosion point of view.

SELECTION OF PUMP BEARING FRAME AND LUBRICATION

In a multi-stage train of pumps, the discharge pressure of one stage is the intake

pressure of the next stage. This pressure acts over the shaft sleeve area of the pump and

results in an axial load. As the number of stages increases, so does the axial load on

each stage.

Warman Type AHP and AHPP pumps are fitted with the Warman high capacity bearingframe designs to cater for the large axial loads. These designs have an extremely high

capacity two row tapered roller bearing at the pump end of the bearing assembly to take



__



both the radial and axial loads. A parallel roller at the drive end carries the radial loads

from the pump and drive.

Bearing lubrication is normally grease, although for high speeds oil lubrication is

available (Type "Y" Bearing Assemblies). The bearing assembly is sealed with the wellproven "Dash 10" (-10) seal design. This seal incorporates grease flushing, Piston

Rings, a V-Ring seal and a flinger. The bearing and seal design is basically the same

for grease and oil, although for oil lubrication, a dip stick is provided to allow checking

of the oil level either stopped or running.

A number of frame alternatives are available. The main factors affecting the proper

choice of pump bearing frame depends on many factors as follows:- number of stages,

pump duty, L10 bearing life specified, type of lubrication, speed, size of pump, type of

drive (belt or direct drive) etc.

Shaft stresses are also an important consideration when selecting a frame. The standardshaft material is generally K1045 steel. Higher tensile steels are available and can be

supplied on request. The type of shaft sealing can influence the design of the shaft and

shaft sleeve. If the sealing method is not standard, it should be brought to the attention

of Warman. The shaft and sleeve design may require special considerations be built

into the pump design.

Warman Engineers can advise on the optimum bearing frame selection to suit each

application.

MULTI-STAGE PUMPS USED AS TURBINES

In some installations, high heads need to be dissipated. This occurs when a slurry (or

water) flows from a high elevation to a lower elevation. A typical example is tailings

flowing from a mine high on a mountain to the plain below. It is possible to run the

flow through a pipeline to a turbine station at the discharge end of the pipeline and

generate power.

It is possible to utilise centrifugal slurry pumps as power generating turbines. The flow

enters the discharge and exits the intake while dissipating head. The pump impeller is

replaced with a turbine runner. The head drop over the turbine generates useful power

that can be fed into the normal electrical grid.

Turbines can be utilised in multi-stage arrangements in the same manner as pumps.

While this manual generally deals with multi-stage (series) pumping, the same general

rules and operating guidelines etc. would apply equally well to multi-stage turbine

installations.

The same basic parameters apply to systems of pumps or turbines. Warman can assist

with the engineering details of either type of system.

GENERAL MULTI-STAGE SYSTEM LAYOUT

Specific design requirements of multi-stage pump unit stations include:-



__



The pump station design should also accommodate the gland water supply, electrical

cables and starters and control instrumentation. Clear space should also be allowed for

pump removal and maintenance.

A control room either within the pump station or nearby is a requirement for systemswhich are computer or PLC (Programmable Logic Controller) controlled. Control

systems can vary from the simple to the complex. Complex systems can allow start-up,

operation and shut-down either completely automatically or but means of a single

button push. Computer controlled systems should cater for all system excursions and or

upsets and cover the full range of variations in sensed parameters. Such systems require

less supervision and should have less incidences of failure. The level of control chosen

will depend on the complexity of the pumping system and costs. Warman can assist

with system overview and general logics if required.

INTERSTAGE PIPING - FIGURE 5

Forces in multi-stage piping can be quite high. Warman recommends the interstage

piping be "rigid" between each stage. Depending on the layout of the pump stages, this

can be achieved in a number of ways. If pipes are not rigid, then this allows the

pressure loads to act directly onto the pump.

The intake diameter of centrifugal slurry pumps is usually larger then the discharge.

This facilitates the design of a telescopic, rigid inter-stage pipe design. A typical design

is shown in Figure 5. The design can be all metal or lined with elastomer. The length

of the smaller diameter pipe can be kept as short as practical to minimise velocities and

hence wear.

The O-ring seals the joint between the telescoping pipe diameters. The flanges should

be rated to the full pressure capability of the pump. Long adjusting bolts allow the pipe

to be adjusted shorter to ease assembly, then lengthened to suit the flange to flange

distance between two pump stages. The number and size of the adjusting bolts should

be sufficient to carry the axial and pressure loads generated when the pumps are

running. Wear and corrosion allowances will also be necessary in some cases.

Figure 4: Multi-Stage Pump Arrangements

a) Parallel shafts

b) Right angle shafts



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Figure 5: Interstage Adjustable Pipe



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Pumps arranged in a staggered line will require a curved interstage pipe. Warman can

assist with the design and supply of interstage piping if involved in the early design

stages of a project.

Specific designs may cater for instrumentation connections or dump connections on theinterstage pipes.

PUMP SEALING

The most general type of seal used is the packed gland. This is due to the reasons that it

is quite robust and simple in operation and can handle high pressures. Warman has

developed gland and materials technology to cater for these high pressure slurry glands.

Other types of sealing are centrifugal (expeller) seals and mechanical seals. Centrifugal

seals are only suited to the first stage of a multi-stage system because they cannot

tolerate high pressure. The pressure that can be generated by a rotating Expeller in a

centrifugal seal is not adequate to counter the high pressures generated inside the pump.

Mechanical seals can be used but generally the available range of seals to cater for high

pressures and slurries is limited. Mechanical seals are also less favoured because they

can suffer catastrophic failures, unlike a gland, where any deterioration or problem will

manifest itself over a reasonable time frame allowing corrective actions to be

implemented.

Some mechanical seal will require a flush to operate satisfactorily. As the provision of

gland and/or flushing water at the correct pressure is often the greatest problem, then it

is worth considering the use of less expensive glands.

The gland pressure varies from pump to pump in a multi-stage pumping station.

Pressures are low on the first stages and increase with the number of stages. It is very

important for correct gland operation, that the correct gland sealing water flow

and pressure is supplied to each and every stage.

PUMP GLANDS AND OPERATION

The high pressure gland is not unlike the standard Warman low pressure gland set-up.

For multi-stage pumps, the gland is normally fitted with a metal lantern restrictor at the

bottom of the stuffing box to control the flow into the pump. Then follows a number of rings of packings (typically four), a packing retainer to prevent the packings from

extruding and finally the gland. The packing runs on a very hard, coated shaft sleeve to

minimise wear. Shaft sleeves are slip fit over the shaft and also reversible. Exact

details including part numbers of the components making up the gland seal pumps can

be obtained from the pumps component drawing.

Follow the instructions in the relevant pump assembly and maintenance manual for the

correct procedures for the fit-up of pump glands.

Glands require a supply of GSW (Gland Sealing Water) to keep the gland cool, help

lubricate the packings, remove heat and also to flush solids away which prevents thegland from wearing. The required flowrates are show in Table 1 depending on the

pump and frame size. When first starting-up and adjusting the glands use the maximum



__



figures. As glands settle down and are adjusted, aim for a flowrate into the gland

somewhere around the minimum figure. The minimum figure is sufficient so that

problems should not be experienced in practice. It is possible to adjust the glands so the

total flowrates are below the minimum figure. However, the whole system can become

more sensitive to system changes and lead to possible gland problems. If the systemworks in a steady state condition this should not be a concern and the glands can be

adjusted to minimise the flow.

Table 1: Gland Sealing Water Flowrates (L/Min)

PUMP MAX MIN

3/2 CC-AHP and 3/2 P-AHP 21 7

4/3DD- AHP and 4/3 Q-AHP 33 9

6/4 EE-AHP and 6/4 R-AHP 42 12

8/6 FF-AHP and 8/6 S-AHP 72 16

10/8 T-AHP 96 24

12/10 T-AHP 96 24

14/12 GG-AHP and 14/12 T-AHP 96 24

16/14 TU-AHP 126 36

20/18 TU-AHP and 20/18 H-AHP 126 36

The GSW pressure must be at least 35 - 70 kPa above the pump discharge pressure.

This is to ensure proper gland operation and that the flow into the pump is sufficient to

flush solids away from the gland area and prevent ingress into the gland which will

cause premature wear.

Note that the requirement for the GSW flowrate and pressure applies to each and every

stage. If some pumps are not operating, the pressure in each individual stage can vary

from its design value. In this case, it is important that the GSW pressures are adjustedto suit each pumps operating conditions. Further, if some pumps are not operating due

to lower system head requirements, then the GSW flow and pressure MUST be supplied

to every pump. Even if the GSW flow and pressure cannot be altered, it is better to

have more flow and pressure than none. If the GSW supply is not adequate, then slurry

will enter the gland and cause premature wear.

In cases when one pump is shutdown it is recommended that its GSW supply is

maintained to prevent gland wear. Further, if a pumps GSW pump is not functioning, it

is recommended that the GSW from pump after it in the train is used to feed the gland

of the pump that is still operating but has no GSW supply. This should work for a short

period until repairs to the GSW pump can be completed. Do not use GSW from thepump before it in the train. The GSW pressure will be too low and cause slurry to enter

the gland.



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Gland packings should be of kevlar or similar high strength materials to withstand the

internal pump pressures. Packings which are too soft will only compress under the high

pressures and cause early seal failure. It is important that the packings can withstand

the pressure so the gap between the packing and the shaft sleeve is maintained and

packings are not extruded out the gland end of the seal. Packing compression couldalso alter the position of the gland components and block the gland sealing water from

entering the gland. No GSW flow will result in early gland failure by wear.

During pump operation, it is important to monitor gland operation. GSW is taking

away the heat generated by friction so can be hot to the touch. Also it is possible for the

gland to become hot. This is not normally a concern. What is of concern is if the GSW

issuing from the gland becomes steam or the gland becomes too hot to touch. In these

situations it is better to stop the pumps following normal shut-down procedures and

ascertain the cause(s). Look for packings which are burnt or worn out. It is possible

that the gland or packing retainer could be rubbing on the shaft.

If problems occur with gland operation it is generally preferred to stop and ascertain the

cause(s) and replace all packings with new packings before re-starting the system. If

gland operation is a concern, monitor the GSW pump system for possible problems of

low flow or pressure.

If a second train of pumps is used as a stand-by, then it is normally essential to isolate

its GSW supply for the operating train of pumps to prevent the GSW taking the path of

least resistance and mostly flowing into the standby pumps. This could starve or

severely reduce flow and pressures to the operating pumps and result in gland problems.

A proper packed gland will require little attention during operation. At first the gland

should be adjusted loose, so the GSW flow is high and plenty of water is issuing from

the back of the gland. Too much is preferable to too little. Over the first day of

operation, gradually tighten the gland nuts, one flat at a time. This could be carried out

every hour say. Do not reduce the flowrate too low during the first period of operation.

Allow the glands to settle down and re-check gland operation at the second start-up and

period of operation. Again, only adjust glands gradually and monitor the leakage out

the back of the gland. It should be a steady steam of GSW and not contain any slurry.

If a gland is operating hot or slurry is issuing from the back of the pump the pumping

system should be stopped and the problem investigated and corrected. Glands will wearout and require replacement with new parts. Operating experience is the best guide to

gland maintenance.

Gland adjustment is generally done in small steps. There is the temptation to back off

the gland on seals which are running hot. Note that loosing the gland may only

exacerbate the problem and lead to gland failure. By loosing the gland, the high

pressure inside the pump can push the packing to the gland end of the stuffing box,

much like a piston. This can change the position of the lantern restrictor and hence

affect the supply of GSW. The gland may only then become hotter compounding the

problem.



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GLAND WATER PUMPS

During pump and system operation, the GSW must be continuous. The gland sealing

water supply pumps must always be started before the main slurry pumps. When

stopping, the gland sealing water must be switched off last. This is to ensure that GSWis always present in the glands and thus avoid any unnecessary wear and tear of the

gland components.

GSW is normally supplied from a dedicated supply. Small positive displacement

pumps are ideal for this purpose. By far the safest method of GSW is to have one GSW

pump dedicated to each slurry pump. This way, the pressures required by each stage

can be adjusted by adjusting the speed or size of each GSW pump. If all the GSW

pumps are the same size and speed, then they become interchangeable and can improve

the GSW supply reliability.

Less satisfactory configurations are:-

• One GSW pump supplying two or more stages. The pressure and flow have to

be carefully adjusted so not all the flow goes into the pump with the lowest

pressure.

• One GSW pump (with a stand-by) supplying all stages. This is really only

recommended when the number of stages is small as it provides little

flexibility. Ensuring the correct pressure and flow is provided to each stage is

difficult to control.

STAND-BY PUMPS AND SPARES

All pumps in a multi-stage pump system are normally the same model. While the

pressure rating of the first stages can be less than the last stages, it is generally

recommended that all pumps have the same pressure rating and the same frame. This

simplifies spares and allows any pump to be replaced with any other pump if and as

required. Having the same bearings, shafts and gland components is also an added

advantage.

The system design, economics and desired availability will dictate if a spare train of

pumps is required to be installed. A spare train allows maintenance work to proceed

more smoothly and can double up as spare capacity depending on the pipeline

characteristics i.e. at times of high tonnage, both trains can be run.

In a two train system (or indeed a one train system) the use of valving to cut one stage

out and cut in another is generally not practical. This is due to the fact that the number

of valves should be kept to a minimum because valves can be an high wear (cost) item.

If only one train of multi-stage pumps is installed the maintenance options is more

restricted. In such cases a spare pump plus spare wearing components will be needed to

be held. As wear in pumps will be more or less the same in each stage, it will be

necessary to carry spares for the whole train of pumps or at least a number of pumps.

As an alternative to spare parts, spare pumps can be kept. If all pumps are the samethey are interchangeable. Hence pumps can be pulled out and refurbished in rotation.

Pumps changed out like this can be designed with a keyway in the baseplate and the



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pump to ease alignment and speed up unit change over. Carried a step further, whole

baseplates, complete with pump, motor and drive can be designed for quick change out.

For further information contact your Warman representative.

It is normally recommended that a spare bearing assembly is also kept.

System requirements would generally change with time. It is possible to install more

pumps than initially required and allow one or two stages to idle with flow passing

through them. These would normally be the stages at the end of the train as these would

affect the overall performance of the train the least. The flow passing through pumps

that are idling will cause such pumps to rotate at a low speed. This should not be a

concern for the pump or drive. Note however, that the gland water supply must be

turned on whenever the train is in operation.

Warman can advise the correct type and quantity of spares to suit your requirements.

POTENTIAL PROBLEMS AND GENERAL PRECAUTIONS

PRESSURE RATINGS - PUMP CASINGS AND PUMP CASING BOLTS

Multi-stage pump system are generally high pressure installations. All pumps and

drives are normally the same to achieve the highest interchangeability and utilisation of

the system. All pumps then are selected to withstand the highest pressure.

Depending on the application, pumps will be selected from the Warman AHP or AHPP

ranges. In broad terms one "P" means the pump is suitable up to a maximum of 3,500

kPa operating pressure, while two "P’s" are suitable to double this (7,000 kPa). Other

ratings are available depending on the pressure requirements. Pumps are generally

statically pressure tested to 1.5 times the maximum operating pressure.

The materials used for high pressure casings and casing bolts is detailed in Selection of

Pump Liners and Materials. Pump casings and bolting constitute a pressure vessel and

should be treated as such. Under no circumstances should holes be made through the

casing. Heat should not be applied to the casing halves. If any casings become worn on

the inside due to the liners wearing through, they should be reserved for the lower

pressure pumps where strength is not as important.

High tensile casing bolts should likewise not be subjected to heating or torques in

excess of those recommended, or anything else that would degrade the bolt strength.

Under no circumstances are the casing bolts to be replaced with ones of lower

tensile strength.

RUBBER LINED PUMPS - VACUUM

Elastomer lined pumps subjected to negative internal pressures can in some cases, cause

the liners to be drawn into the pump and thereby become cut and torn. Often the only

solution will be a pump strip down and re-fit or replacement of the liners.



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In a multi-stage pump system, there are a few situations which could cause negative

internal pressures as detailed below. However as a rule, the pressures would always be

positive and in most situations elastomer liners will not be of concern.

• If the pumps are higher than the discharge of the pipeline, then during shut-down, the line will tend to empty towards the discharge end i.e. the reverse of

run back. The liquid emptying from the line could cause negative pressure in

the pumps, if suitable suction break valves are not positioned along the line. If

the intake of the pipeline is closed off e.g. the intake valve into the first stage

pump is closed or some tramp etc. blocks the inlet pipe, this would probably

cause enough negative pressure to dislodge rubber liners.

• Negative pressures can be generated if the first or second stages are not running

but the following stages are operating. Hence the flow from the feed sump

would have to pulled through one or more stationary pumps. This could

increase the suction losses and thereby create a lower than normal pressure in

the pump(s) not operating. The pressure could be further reduced if there is any

blockage in the intake pipe or sump. If the first stage is running, then there is

little possibility of the pressure reducing in the following stages and causing a

problem. Hence, the first stage should always operate. If the first stage cannot

be operated for some reason, then the risk of liner collapse should be taken into

consideration. This case could also arise if the first pump tripped during

operation and the other pumps kept operating. In this case, system logics could

prevent start-up until the first stage was made available or shut down all pumps

by going into the shut-down mode.

If negative pressure is a known problem or is likely to occur frequently, then metal

liners should be considered as these do not suffer for the same problem as elastomer.

Elastomer is often the best choice of material for wear and depending on your

application etc. Warman can assist with the correct solution to any liner concerns or

problems.

VARIABLE SPEED PUMPS

Variable speed pumps are utilised in multi-stage pump trains for the following reasons:-

• Pumps wear over time and as a consequence, the head generated dropsgradually. If one pump is variable speed it can be speeded up to help maintain

the system head constant.

• Pipelines can wear or perhaps the pipeline route will change over time. A

variable speed pump in such a case can be adjusted to a speed to suit the new

conditions.

• The duty may change with time. Again the variable speed pump(s) can be

altered to suit changing conditions.

• Variable speed units can be used to fill the system at low speeds (and hencepowers) and alleviate any problems with overload of motors particularly when



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attempting to fill an empty pipeline. Here the flowrate could be too high and

overload the drives.

The number of variable speed pumps incorporated in the system will depend upon the

expected extent of changes in the system and duty. In a typical 6 or 8 stage train,usually one or possibly two variable speed pumps are sufficient to cater for all the

expected changing demands. To maximise standardisation all stages should have the

same electric motor drive and the variable speed is normally done with a variable speed

electronic drive connected to the drive of one or more pumps. This is probably the most

efficient, but of course, the type of variable speed drive chosen will depend on the type

and size of drives utilised etc. Variable frequency drives give the added advantage in

some installations that the speed can be increased by an extra amount from 50 to 60 Hz.

Positioning of the variable speed pump(s) in the train can be varied. Generally, the

variable speed unit(s) are positioned at the end of the train. This has less effect on the

overall system operation. Variable speed units can be run at any speed up to full speedto adjust the head to suit the system requirements. If for any reason, the variable speed

pump(s) is not required, it is possible to pump through these pumps without having

them switched on. The pump will rotate slowly (typically at a few hundred r/min) while

the flow is going through the pump. The drive is normally left connected and there

generally is not a problem for the drive to rotate slowly at no load. The resistance of an

idling pump is only small and is approximately equal to 50% to 100% of one velocity

head based on the velocity on the discharge pipe.

Variable speed pumps at the end of a pump train also have less concerns regarding

gland sealing water. Whether the pump is running or just idling, the gland water supplymust be on. In this situation, the variation in GSW pressure requirements will be less

than if pumps in the middle of the train were selected as the variable speed units.

Note that any variable speed pumps that are not started and left to idle, the gland sealing

water (GSW) must be maintained to prevent ingress of slurry into the glands and

subsequent maintenance problems.

The variable speed unit can be placed at stage one. The man disadvantage is that NPSH

could be of concern for the this pump, particularly if the drive is capable of over speed.

It is preferred if the first stage always runs at a fixed speed and duty. This way, any

effects on the system will be minimised and NPSH cannot affect the performance of the

first stage and reduce the head from the total system. Variable speed pumps which areelastomer lined on stage one, are also a concern from a negative pressure point of view.

Refer to Rubber Lined Pumps - Vacuum.

Variable speed pump(s) positioned at intermediate stages are possible but need to be

assessed as to their impact on the overall system. A variable speed drive on the second

or third stages can pose a problem. If the first stage is not operational, and the variable

speed second and third stages are only required to operate at low speed, then the four

stage may have unfavourable suction conditions as it will in effect have to draw the

flow through a stationary pump and perhaps one or two more pumps which are only

running at low speed. This will increase the suction losses and the chances of

cavitation. Further, the pressure will be reduced in the first, second and third stages. If

pumps are fitted with elastomer liners, this may increase the chances of liners being

draw in by vacuum (refer also to Rubber Lined Pumps - Vacuum).



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Warman can assist in the correct selection and positioning of variable speed drives.

BEARING SPEEDS

The pump frame is normally selected by Warman based on the application, power etc.The pump speed is usually fixed at the system design stage and is not normally a

concern. The type of bearing lubrication is selected to achieve the required pump

speeds and provided the bearing lubrication and end cover grease purge maintenance is

carried out, the bearings will give long and trouble free operation.

Situations that could reduce bearing life are as follows:-

Inadequate gland maintenance or insufficient adjustment of glands can allow high

pressure water and slurry to jet out from the gland and impinge onto the pump end of

the bearing assembly. If not controlled, water and contaminants can enter the bearing

assembly and cause premature failures. Pay strict attention to gland maintenance.Regular greasing of the pump end bearing assembly end cover can assist in keeping

contaminants purged from the seal and bearing areas.

If during run-back, the speed increases over the normal running speed, then the

centrifugal forces will increase in the bearing cavities and grease could be flung off the

bearings. Bearing problems could possibly occur a little while later due to lack of

adequate lubrication. Always check the maximum speed against Warman

recommendations. The section on Avoidance of Impeller Loosening - Runback and

Reverse Rotation details cases when over speed could occur along with possible

suggestions in order to limit the over speed.

Incorrect bearing assembly or setting of the bearing fitted end play. This could result in

catastrophic failures depending on the situation. Carry out bearing maintenance in a

clean environment and check the fitted end play of the assembly before assembly into a

pump. Refer to the relevant Warman manual for the type of bearing assembly used.

REQUIREMENTS FOR THE GLAND WATER SUPPLY AND WATER QUALITY

Water used for gland sealing should be clean and generally have the following

properties. Failure to observe these conditions will result in excess time and effort

being spent on gland maintenance (refer also to Gland Water Pumps). Many gland seal

problems are blamed on pump design, when in fact, the seal water system is the majorcause. The most common problems are:-

Suspended And Dissolved Solids

Water quality is an extremely important factor in gland seal operation. The following is

a recommended water quality specification which is attainable with relatively

inexpensive filtration treatment equipment:-

pH 6.5 - 8.0

Solids content:Dissolved: 1,000 ppm (mg/L)

Suspended: 100 ppm (mg/L)



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100 % of +250 mesh (60 µm) particles removed.

Maximum Individual Dissolved Ions:

Hardness (Ca+, Mg+) 200 ppm (mg/L) as CaCO3

Calcium Carbonate (CaCO3) 10 ppm (mg/L)

Sulphate (So4-) 50 ppm (mg/L)

Inadequate Or Excessive Gland Water Pressure

Inadequate pressure results in contamination of the packing by the pumped slurry. Once

solids are imbedded in the packing, they cannot be flushed out and the packing must be

replaced. Seal water pressure should be 35 - 70 kPa above the stuffing box pressure.

Pressure in excess of this only results in more wear on the packing and shaft sleeve.

Inadequate Flow

Like inadequate pressure, this results in contamination of the packing by the pumped

slurry. Often this problem occurs with a seal water system which supplies several

pumps, without flow control to each pump. In this case, the low pressure pump takes

all the available seal water and starves the higher pressure pump. Flow to each gland

should be controlled.

To achieve the above limits, it may be necessary to filter the water to a least reduce any

solids content to the lowest practical.

The gland sealing water supply must be reliable, as slurry pumps must not be

operated without gland water supply, otherwise major gland problems will be

experienced due to the high pressure forcing slurry into the gland region and causing

wear and leakage.

LOW, HIGH FLOW AND WATER HAMMER

Low Flow

Centrifugal pumps must not be operated at very low flowrates i.e. not <15% of normal

BEP flowrate. Conditions which may cause this to occur could occur when the pipelineor intake tank becomes blocked with solids and the pressure is not enough to maintain

the flowrate.

Under low flow conditions, the pumps must be stopped immediately. If centrifugal

pumps continue to operate at low flows, the liquid inside will heat-up and build up

pressure and temperature. The resulting high pressure liquid and vapour can cause

the pump casing to burst and cause property or personnel injury.

High Flow

High flowrate is not normally a concern. Situations which might generate high flowsoccur when filling an empty discharge pipeline or during runback. Further information

is contained in avoidance of impeller loosening - runback and reverse rotation.



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Water Hammer

Water hammer typically occurs in a pump/pipeline system when a valve is closed too

quickly. A pressure pulse is generated which can travel up and down the pipeline at the

speed of sound in the particular slurry. Multi-stage pumps usually have high pressurecasings and bolting, so the effects of pressure surges are generally not a concern.

In any case, the pipeline system design should consider the effects of possible water

hammer. The likelihood of water hammer will increase with the complexity of the

system, particularly if valves are utilised for control. Valves actuation times should be

slow (measured in minutes) to allow the system inertia etc. to slowly adjust as a valve is

shut or open.

Various methods exist to minimise the effects of water hammer. Siphon and vacuum

break valves and/or standpipes are sometimes utilised. Fast acting dump valves which

are electronically energised in the shut position can also dissipate energy by reacting tosudden pressure surges or power outages.

Pipelines must be anchored after the final pump stage to absorb any loads generated by

water hammer and pressure surges.

Power cuts to multistage pumps do not normally create problems apart from possible

run-back and over speed. Refer to Avoidance of Impeller Loosening - Runback and

Reverse Rotation for further details.

AVOIDANCE OF IMPELLER LOOSENING - RUNBACK AND REVERSE ROTATION

Correct Directions of Rotation and Input Torque via Pump Shaft

Each Warman pump impeller features a right-hand impeller thread in its boss and

engaged to the pump shaft, which is screwed to suit the impeller thread. The correct

driven direction of rotation of the impeller, when viewed from the intake end of the

pump, is ANTI-CLOCKWISE for all standard Warman impellers.

The correction rotation of the pump is displayed by a cast arrow on the front of the

pump casing. Note that turbines normally rotate in the opposite direction to a pump.

When the impeller is driven in the correct direction of rotation by means of power

transmitted via the pump shaft, the torque applied to the impeller is transmitted via the

impeller thread. This torque serves to reinforce the fastening of the impeller to the

shaft.

Impeller Loosening

Incorrect directions of rotation and of input torque via the pump shaft

Should power be transmitted to the impeller via the pump shaft but in the incorrect

(CLOCKWISE) direction of rotation, the torque would serve to unfasten (unscrew) the

impeller from the shaft.

This incorrect direction of rotation could result from incorrect rotation of the prime

mover (e.g. from incorrect connection of power supply to an electric motor) or of the



__



output from the drive transmission. In every case, before initial start-up, the pump

should be disconnected from the transmission, preferably at the end of the pump shaft

(i.e. vee belts removed or coupling halves disconnected) and the prime mover started to

allow the actual direction of rotation to be demonstrated. If the direction of rotation is

incorrect, the necessary alterations (e.g. power supply to be correctly reconnected) mustbe carried out to enable the correct direction of rotation to be demonstrated before the

pump is reconnected to the transmission.

Should this precaution not be observed and if power is transmitted via the pump shaft to

the impeller in the incorrect direction of rotation, the (starting and running) input

torques would normally be sufficient to cause the impeller to loosen from its fastened

position on the pump shaft and to proceed (spin) towards the intake side of the pump.

This axial movement is normally arrested by the impeller contacting the intake side of

the pump while the impeller and shaft threads are still engaged.

The shock of this impact is usually sufficient to severely damage the impeller and theintake side liner of the pump. As the thread is still engaged, but the impeller is arrested,

the input torque acts upon the pump shaft to drive the shaft and bearing assembly away

from the impeller. This screw-jacking action normally results in severe damage to the

bearing assembly and can break the adjusting lug off the bottom of the bearing housing.

The danger of an impeller loosening as above is present regardless of whether the pump

is started empty or when containing liquid or slurry.

For multi-stage pumps, as well as the above causes for impeller loosening the following

factors could cause problems of impeller loosening. Generally, if the impeller is tighten

onto the pump shaft during fit-up and then started at least once, then the chances of

impeller loosening are greatly diminished.

Pump Shut-Down On High Static Discharge Heads

When multistage pumps are applied on a duty featuring a very high static head, Z (i.e.

Zd-Zs), the mixture in the discharge system will drain (run back) through the pump,

immediately the pump is stopped. When the resistance to this reverse flow is low, the

reverse flowrate is high. This high flowrate is sufficient to drive the impeller (and

electric motor) in the reverse (CLOCKWISE) direction i.e. as a turbine. As the torque

is being applied to the impeller by the liquid in this clockwise direction, the torque

serves to reinforce the fastening of the impeller to the shaft. However, it is possible forthe speed of this reverse rotation to become significantly high, in some cases resulting

in motor speeds in excess of the maximum safe speed permitted for structural integrity

of the motor rotors.

The maximum speed of reverse rotation will vary from one case to another and will

depend upon a complex relationship of several factors including net positive suction

head, system (hydraulic) resistance to reverse flow, rotational inertia of the rotating

elements in the pump, drive and motor, frictional resistance in the pump and motor

bearings and total volume of liquid run back.

The motor and pump may be protected from dangerously high speed rotation by various

means including:-



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(a) Magnetic brake to prevent any rotation of the pump and motor when the electrical

power is disconnected from the motor e.g. on normal shutdown or power failure.

(b) Centrifugal clutch to interrupt the mechanical drive connection between motor

and drive when the motor is not running in excess of a predetermined speed and isnot running in the correct direction of rotation.

(c) Limiting reverse flowrate e.g. by a non-return valve with a small diameter bleed

hole in the flap to allow run back at a smaller flowrate only.

(d) The discharge valve is used to control the flowrate and is used during shut-down.

The valve would be shut over a short controlled period before shutting down the

pumps, hence not allowing any run back. Prior to this the pipeline may be flushed

with water ready for re-starting.

(e) In emergencies (e.g. power failure) the emergency dump valve normally energisedby power to remain closed, would trigger and most of the pipeline would empty.

Some runback could still occur but at a smaller flowrate.

Effects Of Unrestricted Runback And Reverse Rotation

Immediately upon runback being completed, on a gravity-fed installation, liquid may be

present in the pump hopper while the pump and motor are still rotating in the reverse

(CLOCKWISE) direction. Under these conditions, the rotational energy available from

the rotating elements (particularly where a heavy motor rotor is employed) will be

applied to drive the impeller clockwise and pump the liquid back into the discharge

pipe. (This pumping would not occur if the intake system was completely scuttledduring the run back). As the impeller would be driven in the incorrect direction by the

input torque via the pump shaft, the torque would tend to unfasten the impeller from the

shaft. This could result in damage to the impeller and intake side of the pump and

damage by screw-jacking the bearing assembly as described above. In the event that all

of the rotational energy is dissipated before any significant damage is caused to the

pump, all rotational motion would cease with the impeller partially unfastened from the

shaft, i.e. the impeller probably being lightly arrested at the intake side of the pump.

This is a dangerous condition as leakage can occur past the impeller O-Ring into the

bearing assembly as on the next start-up, the pump shaft would very rapidly draw the

impeller back towards its fastened position. The impact of this sudden axial movement

of the impeller is often sufficient to damage the shaft sleeve, bearings and othercomponents. This problem is not commonly encountered in practice but is more likely

to occur when:-

(a) The initial fastening of the impeller is not sufficiently tight e.g. after a new

impeller has been fitted to the shaft without sufficient torque applied in the fitting

operation, and

(b) The pump has not been operated for a sufficiently long period to allow the

impeller fastening to be further tightened by normal start-up and operating

torques.

In general, for any proposed application where the value of the system static head (Z)

exceeds 50 metres and the length of the discharge pipeline (Ld) exceeds 200 metres, all



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relevant details on the application should be referred to Warman for analysis and

specific advice regarding precautions required to avoid the problems described above

and to assist in the design or selection of brakes, clutches or other suitable protective

equipment.

Stationary Pump - Forced High Flowrate

In some cases, a very high flowrate can be forced into the intake side of a stationary

pump. This can occur under certain conditions during the start-up of multi-stage pump

units. Refer to relevant sections on filling the Pipeline. As the very high flowrate of

liquid passes through the pump intake, impeller and casing to the discharge pipe. The

reaction serves to rotate the impeller in a ANTICLOCKWISE direction, which tends to

drive the pump shaft, drive transmission and electric motor in the normal direction of

rotation.

Loosening of the impeller may then occur if:-

(a) The initial fastening of the impeller is not sufficiently tight, and

(b) The rotational inertia of the rotating elements in the motor and drive as well as the

frictional resistance in the pump and motor bearings are sufficiently high to

largely resist the torque transmitted by the impeller.

In general, the loosening of the impeller under these conditions, is relatively gentle.

The external moving parts (pump shaft, drive transmission and motor shaft) may

possibly be seen to rotate for a short while then stop, while liquid is being forced

through the pump. The stopping would indicate that the loosened impeller has becomegently arrested at the intake side of the pump.

Subsequent starting of the pump could lead to leakage into the bearing assembly and

damage to O-Rings and other components as previously described.

This problem can be avoided by several means:

(a) Avoiding very high flowrate during the start-up of multi-stage pump units. e.g. by

firstly filling the discharge pipeline with water at a controlled low flowrate.

(b) Utilising a centrifugal clutch in the drive to allow the pump impeller and shaft tofreely rotate together, without any resistance from the motor and drive.

(c) Ensuring beforehand that the impeller is securely fastened to the shaft.

Diesel Engine Drives

While not commonly used for multi-stage pumps, diesel engine drives need special

attention. A clutch should be provided to release the drive from the pump. Also diesel

engines when stopped suddenly, can allow the impeller inertia to unscrew the impeller

from the shaft thread. For specific recommendations refer to Warman.

SYSTEM DESIGN - INSTRUMENTATION



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Instrumentation can be simple or complex. The final choice is tied up with the type of

system control desired for day to day operation. Computers or PLC controllers can be

utilised for control depending upon the level of manpower and operating cost level

considered desirable. System controls will require inputs from the pipeline and pumps

to achieve the level of control desired.

In a simple system, the instrumentation will usually be minimal. Its main function will

be to display and record various parameters such as tonnage or power consumed.

Adjustments to the system would typically be made manually based on the recorded

figures. Pipeline operation could tend to fluctuate more using this technique.

In more complex systems, parameters such as flowrate, pressure, density etc. could all

be measured and monitored by the computer and control adjustments made

automatically in real time. If density was to increase say, make-up water can be added

at the sump or variable speed pumps could be adjusted to maintain the specified

flowrate to prevent possible pipeline sanding and blockage.

The most useful operating parameters that can be measured and utilised for control

purposes are as follows:-

• Flowrate

• Discharge head after the last pump in a train

• Density of sump inflow or in the pipeline - use with flowrate to calculate

tonnage

• Pressure either side of the main discharge valve

• Make-up water inflow

• Intake sump level

• Pump speed and power draw (kW and Amps)

• Run indication of pumps operating, idle or on variable speed

• Gland water pumps - run indication

• GSW flow and pressure into each stage (operating and standby)

• GSW alarm conditions

• Low and high flowrate alarm conditions

• Valve positions - intake, discharge, dump and drain

• Sump level

• Quantity of flush water available

The measured parameters would be duplicated if more than one train of pumps is used.

Due to the differences in the various systems and the parameters measured and the

degree of control utilised in operating the system, it is not possible to set down hard and

fast rules on instrumentation. Pressure, wear, back-up, accuracy and calibration

requirements for instruments will all need to be assessed before instrumentation are

selected for slurry service. Generally, the least instrumentation that can be utilised to

measure and control the system the better for reliable long term operation.

Instrumentation should be checked regularly to ensure measurements are not drifting.

Simple water purged pressure gauges can be used to check pressures, orifice plates forflow. Cross checking calculated tonnage’s with figures from other parts of the plant can



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also assist. Selection of any instrumentation should be considered in the early stages of

the system design.



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SYSTEM DESIGN AND SCHEMATIC LAYOUT- PIPELINE AND VALVES FIGURE 6 AND 7

Multi-stage pumps and pipeline design and layout will vary from one installation to

another. Systems can vary from SIMPLE to FULLY CONTROLLED or something in-

between. The two extremes are shown schematically in Figure 6 and 7.

Figure 6 shows a simple system in terms of valving and instrumentation. This would

typically be manually operated. Figure 7 shows a fully valved and instrumentated

system, that could typically be semi or fully automatic in operation.

System operation and procedures will be discussed in terms of the two systems -

SIMPLE and CONTROLLED - as shown in Figures 6 and 7. Basic procedures are

much the same irrespective of the type of system. Hence, while the step by step

procedures are more general in Start-up Procedures and Shut Down Procedures, they

can be utilised and applied to any system without too much change. The degree of

instrumentation and control should only influence how the various basic procedures arecarried out and not dictate any changes to procedures.

PIPELINE

The pipeline for multi-stage slurry pumps will have to withstand the pressure generated

by the pumps as well as providing satisfactory wear life. The pipeline should be

anchored after the last pump to withstand all pipe forces without transmitting any pipe

forces to the pumps.

The pipe wall thickness should withstand the full internal pressure (or any expected

peak or surge pressures) while maintaining a wear allowance. Pipes can typically belined to reduce wear or a program of pipe rotation undertaken at set times to even pipe

wear. Joints in the pipe should be as smooth as practical inside to minimise turbulence

and wear at the joints. Pipelines can be constructed from different wall thickness to suit

the changing pressure conditions along its length. Different materials can be utilised -

say hardened steel in the high pressure region near the pumps, perhaps with the end of

the pipeline in Polyethylene for ease of handling.

Interstage piping is covered in Interstage Piping.

VALVING

As a basic rule, any control valving should be kept to a minimum to provide for basic

system control to satisfy the system design. Control valves will wear over time and

cause extra maintenance. Other valving such as intake valves, drain and dump valves

which only provide ON-OFF operation are not such a problem in this respect.

In a SIMPLE system with only a few pumps and a short pipeline, satisfactory operation

can be achieved without control valves. ON-OFF type valves could be required e.g.

intake valve.

In more complex systems (say five or more pumps and perhaps two trains of pumps

plus a long pipeline) controls will be necessary. Controls will entail use of controlvalves. Generally, the only critical valve will be the discharge valves. Wear and

maintenance in discharge valves can be minimised if they are utilised in the



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correct manner viz. the valve is mainly used as an ON-OFF valve during normal

operation and any periods requiring throttling are kept to an absolute minimum.

This will maximise the valve life. Systems utilising discharge valves should be

designed in this manner.

Valves used for ON-OFF use (intake, dump and drain) can be valves generally designed

for slurry. Intake valves could be low pressure knife gate types. Dump and drain valves

could be ball or plug type valves suitable for slurry. Valve seats should be specially

design to minimise particle entry and wear.

Discharge valves should be able to withstand the full system pressure. Typically ball or

plug type slurry valves will provide the best service life. Valve seats should be

designed to minimise particle entry and wear. Seat flushing may also be possible on

some models. Velocities should be kept low through the valve to reduce wear.

Throttling should be minimised through the valve to prolong valve life.

Dump valves can be positioned at the pumps. Alternatively, a dump valve positioned

further along the pipeline may provide more control in case of emergencies. In this

instance, if the dump valve is electrically activated to remain in the closed position,

when a power outage occurs, the dump valve will open and release some of the slurry in

the pipeline to a suitable ponded area. This could help to reduce runback and effects of

reverse flowrate.

Non-return type valves are generally not recommended for multi-stage service. Unless

they can be damped or controlled and activated over long periods (e.g. by a small bore

by-pass around the non-return valve or some mechanical damping system mounted on

the valve) then they should be avoided. Sudden closing of non-return valves can cause

severe water hammer problems. Pipes have been known to burst under these forces.

The high forces generated also could cause damage to pipe and pump foundations.

When properly damped, non-return valves can assist to control system operation e.g. by

limiting the rate of runback after a power outage. This maybe an important

consideration for a long pipeline when insufficient runback storage is available at the

pump station.

Another type of device that could find use is a mechanical bursting disk or valve. At a

specified pressure, the disk ruptures and high pressure is allowed to escape. Once

ruptured, the device needs to be replaced. Such a device could be used as a last safetymeasure to avoid pump and pipeline damage. Generally, if a system is well engineered,

and adequate controls are built-in, there should not be a requirement to include a

bursting device. Typically if the flowrate reduced to an unsafe value and the pipeline

and intake blocked, then it is probably unlikely that the bursting device would see the

high pressure in time or at all because of the pressure would not be transmitted through

solid slurry very effectively.

INTAKE SUMP AND PIPELINE FLUSHING

Intake sumps will vary in their design depending largely on the type and quantity of

slurry needed to be handled. Designs can vary from large agitated slurry tanks toconstant density sumps.



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Slurry should enter the intake sump with the minimum disturbance to avoid air

entrainment and thereby reduce any risk of entrained air affecting system stability.

Sump bottoms and first stage intake pipes should ideally slope towards the pump to

minimise built up of solids in the sump and reduction of sump volume. Pipework to the

first stage pump should be as short as possible to reduce intake losses.

Sump size will depend initially on the slurry flowrate and the system design. The

system may operate continuously or possibly in a batch mode. Further considerations

will take into account the amount of system runback and possible storage in an agitated

intake sump. Sump overflows need to be generous to provide for unexpected runback

without sump overflow.

Make-up water connections to the intake sump should also be provided. This will allow

dilution of the slurry density if required. During pipeline filling the make-up water can

be utilised. Make-up water supply will need to be sufficient to supply the full needs

during filling. During shut-down it is good practice to flush the pipeline with waterbefore final shut down. The make-up water supply will also serve this purpose. Water

that is used for plant water or water returned from a settling dam will normally suffice

as make-up water.

If the slurry is known to take a long time to settle in the pipeline, then it is possible to

leave the pipeline filled with slurry to minimise start-up delays. In some cases,

pipelines can be left for 24 hours and can be re-started with too much problem. If

pipeline start-up is known to be a problem, then flushing the pipeline with make-up

water will assist. Flushing need only be carried out for sufficient time to reduce the

concentration in the pipeline sufficiently to obviate any re-start problems. Only if thepipeline is going to be shut down for extended periods will it be necessary to completely

flush the line.

By using a discharge or non-return valve, the pipeline can be left full of slurry or

flushed after system shutdown, thereby keeping it primed ready for the next pipeline

start.



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Figure 6: System Design and Schematic Layout - Simple System



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Figure 7: System Design and Schematic Layout - Controlled System



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VARIABLE SPEED PUMPS AND POSITION

To provide system flexibility, it is normal to use one or more variable speed pumps in a

train. Variable speed pumps allow the head to be varied to cater for pump and pipeline

wear, as well as changing duties.

The variable speed units are placed where they will be the most use. The following

factors need to be considered:-

• If the pipeline requires to be filled often, then it may be best to have the first

stage variable speed. This way the flowrate to fill the pipeline can be

controlled while also controlling the NPSH of the first pump to avoid

cavitation.

• If system control is paramount, then having the variable speed pumps on the

last stages should prove most beneficial. This way the system can be startedand stopped without any problems and the exact number of stages to satisfy the

Head requirements can be started. The variable speed pumps may be started or

run at any speed up to the maximum. Pumping through pumps which are not

running is not a problem. The flow will turning these pumps at a speed which

is fraction of the full speed (say a few hundred r/min). Note that the gland

sealing water must be operating and preferably at a pressure which is 35 -

70 kPa above the discharge pressure for that stage.

• Variable speed pumps can be used on any of the stages in between. However,

with rubber lined pumps, it is important to ensure that the first stage is always

operating. Otherwise, the succeeding stage can create a negative pressure in the

first stage and cause the rubber liners to collapse into the pump. For this

reason, variable speed pumps in the in-between stages is generally not a

preferred option. Note that system controls could be arranged to prevent the

operation if the first stage is non-operable.

BASEPLATES AND PIPE ANCHORS

Warman "CV" style drives, with the motor mounted above the pump and driving the

pump via a belt drive are available on pumps to approximately 8/6 size. This should be

considered for mine dewatering applications when the smaller footprint of the CV drivecan save considerable space and cost.

Warman can design and supply any type of baseplate to suit the application and type of

drive. Larger pumps are often direct driven from the motor or a gearbox between the

pump and motor reduces the motor speed to suit the pump. Gear Box drives can be

fully engineered with the necessary cooling devices integrated into the design.

FIRST STAGE PUMP

The selection of the first stage pump deserves special attention. NPSH maybe a specialconsideration and require selection of a pump of another type than used in the main

pump train. Warman dredge and gravel pumps with low NPSH required offer an



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alternative selection for systems with low NPSH available. Refer also to Variable

Speed Pumps and Position.

Another consideration for the first stage is the type of liner. Elastomer liners can be

subjected to damage if the pressure inside the pump becomes negative. For furtherinformation refer to Rubber Lined Pumps - Vacuum.

SYSTEM ANALYSIS

As well as assisting with pump, bearing and drive design and selection, Warman can

assist with the overall system design for multi-stage pump systems.

Moments of inertia of pump and drive as well as torque-speed curves can be prepared to

assist system analysis. Assistance and analysis using four quadrant performance

characteristics is available. If the system is designed by a third party, then they would

normally be responsible for the overall system logic and analysis. The type and extent

of any system analysis will depend upon the complexity of the system and the degree of

automatic control required.

Centrifugal slurry pumps are generally quite robust. The most critical item will be the

gland sealing water. The GSW supply must be reliable and interlocked into the

main pump drives, so the main pumps cannot operate unless the GSW supply is

functioning.

The main areas for system analysis will concern such items as follows:-

• Maximum system pressure• Maximum pressure from water hammer effects or power outage and runback

• Maximum reverse flowrate

• Maximum power draw particularly during pipeline filling and start-up

• Expected variations in flow, head and density

• Minimum pipeline velocity

• Minimum flowrate

• Internal (negative) pump pressures under abnormal operating conditions

• Effects of drain and dump valves on system shutdown - normal and emergency.

Depending upon the results of the analysis, various contingencies can be built into the

computer or PLC control software. Single button operation is possible to carry out

normal start-up and shut-down sequences, as well as handle emergency situations.

In practice, multi-stage pumps operate with few problems. The systems generally

operate at more or less a steady state, and if computer controlled, will operate with

minimum manpower. The duty flowrate, head etc. normally only varies slightly from

the design conditions and hence system excursions are fairly rare.



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START-UP PROCEDURES








SIMPLE and CONTROLLED - as shown in Figures 6 and 7. Basic procedures are

much the same irrespective of the type of system. Hence, while the step by step

procedures are more general in this section, they can be utilised and applied to any

system without too much change. The degree of instrumentation and control should

only influence how the various basic procedures are carried out and not dictate anychanges to procedures.

The first steps before start-up of a multi-stage pump train is usually filling of the

pipeline and preparations for start-up. The following section covers filling the pipeline.

FILLING THE DISCHARGE PIPE

Multi-stage pump units are usually employed on long-distance pipelines. These

pipelines are initially empty, i.e. containing air only. As the resistance to flow will be

zero when a pipeline is empty but increasing as the pipeline becomes filled, very highflowrates could result from pumping into an empty or partly-filled pipeline. Unless

operators are experienced with all aspects of the pipeline operation or controls can

account for start-up procedures with an empty line, it is preferred that the first

operation is to fill the pipeline with liquid. The system can be started up with water

or slurry but it must be pointed out that starting with slurry could exacerbate any

problems. For settling slurries, the flowrate used for filling would need to exceed the

settling velocity of the slurry to avoid possible pipe blockage problems.

Some systems will have a check value in the discharge pipe to prevent run back. This is

only possible for slurries that do not settle with time and cause pipe blockages. Also in

emergencies when the pump system is not planned to be out of operation for anyextended period and the slurry cannot be afforded to be dumped from the line, then the

pipeline may be left full. In other instances, when pipelines are filled with slurry, the

time before start-up of the system may be critical to avoid solid deposition in dips in the

pipeline.

RECOMMENDED START-UP AND FILLING PROCEDURES

(a) Ideally, the pipeline should be filled with clear water with the pumps stationary.

This may be achieved by introducing water into the highest point in the pipeline

or suction system.

If this is not possible, the water may be introduced into the suction system for

pumping into the discharge system. It is preferable to limit, i.e. control the



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flowrate of water introduced into the suction system to a small value, e.g. around

25% of the proposed duty mixture flowrate, and to maintain this small flowrate

until the discharge pipeline has been completely filled, over its entire length, with

water.

This operation should be commenced with the first stage pump only running. The

2nd and subsequent stages would be started only as required to maintain this

limited flowrate through the system during the filling operation.

This procedure has the advantages of avoiding excessively high flowrates and

consequently excessively high power consumption by any of the drive motors,

while the pipeline is being filled with water. Excessively high flowrates also

introduce the risk of loosening the impellers on pumps which are not running at

the time. The tendency for impeller loosening normally occurs only on new

pumps or pumps with newly-fitted replacement impellers. These impellers may

not have received sufficiently tight fastening during assembly or re-assembly or asa result of the tightening torques generated during start-up and running, to resist

the loosening torques. Refer to Section on Avoidance of Impeller Loosening.

(b) Obviously, as the time required to fill a long distance pipeline at the limited (25%)

water flowrate may be considered by some clients to be impracticably lengthy, it

may be necessary to increase the flowrate to a higher limited value, BUT

preferably to less than 100% of the proposed duty mixture flowrate to avoid

excessively high flowrates or high power consumption. Monitor the flowrate and

power absorbed by each pump. If the power drawn is well within the motor

power, it would be satisfactory to continue to increase the flowrate to reduce thefiling time. Most system will produce a reducing fill flowrate with time because

the pipe resistance and static head is increasing. In this case starting up another

pump in the train can help maintain the filling rate.

START-UP AND FILLING WITH UNLIMITED WATER SUPPLY

In any case, when it is necessary to fill the pipeline with water as quickly as possible, it

should be assumed that the flowrate of water which can be introduced into the suction

system is unlimited, i.e. the flowrate discharged at any time is simply that estimated for

the combination of pump (or pumps) actually running with the suction system and

discharge system, the latter being initially empty and becoming progressively filled.

Under these conditions, it is necessary to examine the system start-up and filling

characteristics to determine:-

(a) The optimum starting (time delay) sequences which should be adopted to achieve

minimum power consumption on each motor and

(b) Whether the specified rated (mixture duty) power output of any motor or motors

may have to be increased to cover the estimated length of time of and value of

maximum power consumption during the optimum starting (time delay)

sequences.



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NOTE: Obviously, initial filling of a pipeline with slurry mixture would exacerbate the

problems of initial filling with water and should be avoided. However, it is possible to

examine the system start-up characteristics for cases where it is suspected that there

may not be sufficient supervision and control to ensure that a start-up and filling on

mixture would never occur. Details can be referred to Warman for assistance.

Refer to Start-up with Line Full and Start-up with Line Empty for the proper procedures

on how to plan and calculate the pump Start-up procedures.

STARTING AND FILLING WITH VARIABLE SPEED PUMPS

A variable speed drive on the first stage pump may be employed to limit the values of

amps and kW throughout the entire start-up path. This may assist in avoiding the need

for high motor ratings, simply to cater for start-up conditions, providing that adequately

sensitive speed control can be applied.

START-UP WITH LINE FULL

Procedures for SIMPLE and CONTROLLED system start-up are set out below as step

by step instructions. As previously discussed, each system will be somewhat unique but

procedures can be established by following the basic procedures as set out below.

Procedures may vary from one start to another depending upon the conditions existing

before start-up and the procedures adopted for shut-down.

SIMPLE SYSTEM (FIGURE 6) START-UP WITH LINE FULL

For a SIMPLE system, a discharge valve is probably not installed. To maintain the linefull, it is possible that a full bore non-return valve can be fitted to the discharge. The

pipeline can be filled using any of the methods as detailed in Filling the Discharge Pipe.

1. Establish that all pumps are in serviceable order and turning freely. Motor

rotation should be checked if the pumps have not previously run.

2. Establish that the drive motors are in serviceable order. Visually check coupling

and drive alignment and tension and that drive guards are securely in place.

3. Establish that the gland sealing water supply pumps and system are in working

order.

4. Start the gland water pumps and check that any flow and pressure indicators are

normal. Alternatively, visually inspect water is issuing form the back of the

glands. It is recommended that the GSW pumps be interlocked with the main

pump starters. If the GSW pumps are not operating the slurry pumps cannot be

started. All pumps whether running or idling must have their gland sealing

water supply turned ON whenever the pipeline is being operated . This is to

avoid ingress of slurry into the gland and subsequent gland problems.

5. Introduce slurry into the intake sump. Initially the make-up water can be turnedfull on to help dilute the slurry in the initial start-up phases. Open the intake

valve.



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6. Open the drain valve and start stage one pump. Run stage one for approximately

one minute to fill the other pump stages with slurry and remove the air. Shut the

drain valve. If the intake sump level is high, then it is possible to simply open the

intake valve and allow the static head from the sump to purge air from the pump

train without starting stage one.

7. If the system is fitted with a non-return valve in the discharge line, it is possible to

start each stage in turn (2, 3, etc.) allowing say one minute between starts. This

will ensure each stage starts properly and keeps the current draw to a minimum.

8. As the number of stages running increases, the pressure generated will increase.

When the pressure is high enough to lift the non-return valve, flow will

commence in the pipeline, slowly at first and then developing into the full flow.

Power drawn by each stage should be fairly uniform, as each stage will be running

at the duty speed initially at low flow, but as the flowrate increases the head

power drawn will increase in each stage.

9. The system can be slowly started by only starting the required number of stages to

commence flow. Once the initial flowrate is established, further stages can be

started at intervals predetermined as required to increase the flow to the final duty

flowrate.

10. OPTION: If an ON-OFF discharge valve is fitted to the discharge pipe, then the

system can be started similarly to the steps (6) to (9) above. An alternative

scheme would be to start stage one pump to purge air via the dump valve (then

shut the drain valve), then start the remaining stages in sequence allowing a short

period between to minimise current draw. Once all pumps were started, the

discharge valve would be opened slowly by hand. The power draw will increase

uniformly on each stage as the flowrate increases.

11. The time to achieve full flowrate, will depend on the system characteristics.

Check any instrumentation for normal operation. If the slurry was initially diluted

with make-up water, gradually reduce the make-up water over a reasonable time

(say 30 minutes) and build up to the final density.

12. Visually inspect the pumps for correct gland operation. Adjust the glands

gradually if pumps are new or new packings have been installed. Check the pumpand drive bearing housings by hand to ensure bearings are not overheating. Check

the pumps, gland supply lines and slurry pipes for leaks.

13. Continue to monitor the system and pumps as required. Maintain intake sump set

point levels manually or by use of the variable speed units. Minimum levels that

could cause cavitation are to be avoided. If the start-up was carried out with

water or dilute slurry then the head required will be less than with slurry. As the

slurry density in the pipeline increases to normal, the head required and the power

draw will increase accordingly. In some cases another stage may need to be

started, or the speed of the variable speed units increased.

14. As system demands change, the variable speed drive(s) should be adjusted to meet

the new requirements.



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CONTROLLED SYSTEM (FIGURE 7): START-UP WITH LINE FULL

The procedures to start-up a CONTROLLED system would be almost identical to those

of a SIMPLE system only most or all the procedures will be carried out by computer

control.

In a fully automatic system, it will only be necessary to press the "Start" button. If the

pipeline is not filled, then the system should automatically fill it using any of the

methods as discussed in Filling the Discharge Pipe. Other systems with semi-automatic

controls will control some of the basic procedures. In a CONTROLLED system it

would be usual to have a pneumatic or hydraulically controlled discharge valve. Other

valves would be similarly actuated by remote means. As the pipeline has been filled

previously, the discharge valve will be shut. In general terms the basic procedures

would be as follows:-

1. Establish that all pumps are in serviceable order and turning freely. Motorrotation should be checked if the pumps have not previously run. Set the number

of stages to be started and the status of each stage in the computer set-up screen to

allow correct start-up sequences to be determined by the built-in logic.


and drive alignment and tension and that drive guards are securely in place. Set

the status in the start-up screen as required.


order. Set the status of each pump in the computer set-up screen to allow system

logic to determine the correct GSW pumps to start. It is recommended that theGSW pumps be interlocked with the main pump starters. If the GSW pumps are

not operating the slurry pumps cannot be started.

4. Start the gland water pumps and check that any flow and pressure indicators are

normal. In a controlled system, the computer would check these items. Any

abnormal operation of GSW pumps should be an alarm condition. Problems

would need to be rectified before the system will progress to the next stage of

start-up. All pumps whether running or idling must have their gland sealing

water supply turned ON whenever the pipeline is being operated. This is to


5. Introduce slurry into the intake sump. Initially the make-up water can be turned

full on to help dilute the slurry in the initial start-up phases or the system can be

started up on water. Open the intake valve.

6. Open the drain valve and start stage one pump. Run stage one for approximately

one minute to fill the other pump stages with slurry and remove the air. Shut the

drain valve. If the intake sump level is high, then it is possible to simply open the

intake valve and allow the static head from the sump to purge air from the pump

train without starting stage one. Shut the drain valve.



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7. As the discharge valve is shut, it is possible to start each stage in turn (2, 3, etc.)

allowing say one minute between starts. This will ensure each stage starts

properly and keeps the power draw to a minimum.

8. As the number of stages running increases, the pressure generated will increase.When the pressure on either side of the discharge valve is sensed to be equal, the

discharge valve can be slowly opened to the full open position. A variable speed

pump can then be started and gradually increased in speed to its full speed. Flow

in the pipeline will gradually increase. Power drawn by each stage will gradually

increase as the flowrate increases.

Alternate: If variable speed units are not available for starting at the time that the

pressure is sensed to be equal on either side of the discharge valve, it is

permissible to start one more stage. The pressure on the pump side of the valve

will be higher. As the discharge valve is slowly opened, the higher pressure will

start to induce flow in the pipeline. Flow will take some time to develop becauseof the mass and inertia of the fluid in the pipeline.

9. Once the initial flowrate is established, further stages can be started at intervals

predetermined as required to increase the flow to the final duty flowrate. During

this phase variable speed units can be increased in speed to the maximum before

being switched off and fixed speed units started up. If the pipeline is started using

dilute slurry or water, the head and power will be lower than the final slurry duty.

Hence variable speed units can be started and maintained at relatively low speed

while the density is low. As the slurry density increases in the pipeline, the head

and power demands will increase. The V/S units can be controlled to increase inspeed to match the increase in extra demand.

10. The time to achieve full flowrate, will depend on the system characteristics.

Check any instrumentation for normal operation. If the slurry was initially diluted

with make-up water, gradually reduce the make-up water over a reasonable time

(say 30 minutes) and build up to the final density. As the density increases,

further stages may have to be started due to the increased head and power

demands until the final duty is achieved. Controls can automatically sense these

changes and balance the number of stages against the demand.

11. Controls should monitor gland function, bearing temperatures plus power drawand pipeline flow and head. It would be difficult to monitor and control gland

leakage rates so it is strongly recommended that the pumps are visually inspected

for correct gland operation. Adjust the glands gradually if pumps are new or new

packings have been installed. Also visually check for any leaks.

12. Controls should continue to monitor all functions of the operation. Intake sump

set point levels, flowrate, density and tonnage can be controlled by use of the

variable speed units. If the start-up was carried out with water or dilute slurry

then the water head required will be less than with slurry. As the slurry density in

the pipeline increases to normal, the head required and the power draw will

increase accordingly. In some cases another stage could need to be started, or thespeed of the variable speed units increased. Computer logics could allow the



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density to ramp up at a set rate, and the number of pump stages and variable speed

units adjusted progressively.

13. As system demands change with time, the variable speed drive(s) should be

adjusted to meet the new requirements. If flowrate or head in the pipeline need tobe reduced, one stage may be stopped and allowed to idle with flow passing

through it.

14. If the system demands increase beyond the capacity of one train, then a second

train (if installed and available) could be started to meet the increased demand. It

is possible for each train to have its own pipeline, or for the two trains to share a

pipeline. Before starting another train, the same basic steps should be followed:-

• Fill the pipeline if not already filled.

• Switch on GSW

• Purge air from the pump train via the drain valve• Start pumps stages until pressure across the discharge valve is balanced

• Open discharge valve

• Start further stages and/or increase the speed of V/S units to increase the

flowrate

• Increase density and adjust the number of running pumps to meet the

required duty

• Monitor systems and allow controls to adjust to meet set points

• readjust set points as required.

START

-UP

WITH

LINE

EMPTY

FIGURES

8, 9, 10, 11, 12AND

13

Start-up with the pipeline empty would apply to SIMPLE or CONTROLLED systems.

The procedures would be very much the same and will not be differentiated in the

following sections. The method set out below for establishing the start-up path would

typically be used in a SIMPLE system to calculate the time intervals between start-up of

successive stages. This is necessary to limit power draw and effects of high flow.

For a CONTROLLED system, the method set out below is equally valid, but with the

use of appropriate computer logic, instrumentation and controls, the system would

establish its own start-up path. This would have the advantage of allowing start-up to

proceed with varying conditions at start-up. Set points could be managed by thecomputer to allow the optimum start-up path to be used irrespective of the starting

conditions. Starting conditions could be input into the computer before commencement

of start-up procedures.

Start-up of a multi-stage system can be controlled in virtually all systems by

establishing the correct start-up path. Use of the discharge valve for controlling the

flowrate into the pipeline is not recommended nor desirable for the valve. In general

terms the basic procedures for either a SIMPLE or CONTROLLED system would be as

follows:-

1. Establish that all pumps are in serviceable order and turning freely. Motorrotation should be checked if the pumps have not previously run. In a

CONTROLLED system set the number of stages to be started and the status of



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each stage in the computer set-up screen to allow correct start-up sequences to be

determined by the built-in logic.


and drive alignment and tension and that drive guards are securely in place. Setthe status in the start-up screen as required.


order. Set the status of each pump in the computer set-up screen to allow system

logic to determine the correct GSW pumps to start. It is recommended that the

GSW pumps be interlocked with the main pump starters. If the GSW pumps are

not operating the slurry pumps cannot be started.

4. Open the discharge valve fully.

5. Start the gland water pumps and check that any flow and pressure indicators arenormal. In a controlled system, the computer would check these items. Any

abnormal operation of GSW pumps should be an alarm condition. Problems

would need to be rectified before the system will progress to the next stage of

start-up. All pumps whether running or idling must have their gland sealing

water supply turned ON whenever the pipeline is being operated . This is to


6. Introduce slurry into the intake sump. Initially the make-up water can be turned

full on to help dilute the slurry in the initial start-up phases or the system can be

started up on water. Open the intake valve.

7. Open the Drain valve and start Stage One Pump. Run Stage One for

approximately one minute to fill the other pump stages with slurry and remove the

air. Shut the Drain valve. If the intake sump level is high, then it is possible to

simply open the intake valve and allow the static head from the sump to purge air

from the pump train without starting Stage One. Shut the drain valve. If Stage

One is variable speed, it can be started at low speed to reduce power draw to

acceptable levels. This is described in more detail below.

8. Follow the instructions and example below to establish the Start-up Path and

suitable times between starts.

9. After the system start-ups and the duty stabilises, any changes to system

performance can be made by means of the V/S units or by starting or stopping one

or more stages.

INTRODUCTION TO START-UP PATHS

The initial Instantaneous System Resistance (ISR) is virtually zero because of the

absence of any friction and static head in the discharge side of the system. However,

the flowrate, Q, will quickly accelerate from Q = 0, at zero pump speed, to Q = a value,

at full speed, which will be limited by either:-

• The ISR of which the characteristic SR (System Resistance) curve will vary as

the pipeline is progressively filled with water.



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• Cavitation in the first Stage Pump (NPSH Limitation).

If all stages were started simultaneously, the absence of any initial resistance in the

discharge side of the system would probably result in extended operation in cavitation

of the first stage pump and overloading of all or most of the drive motors, until a

sufficient length of the pipeline has been filled with water. Accordingly, it is necessary

to arrange for a timed sequence of starting each of the successive stages to avoid

excessive overloading of any of the drive motors, drives and the electrical supply,

distribution and control systems.

As pumping is commenced into the empty pipeline, and the water progressively moves

along the pipeline (displacing air), the varying ISR will be dependant, primarily, upon

the net static head, Z, and the total equivalent length of pipe, L, both values taken for

the point in the pipeline at which the water has just arrived.

In many instances, the pipeline may follow an uneven ground profile, i.e. rising andfalling, when the value of Z will vary significantly, possibly between positive (+ve) and

negative (-ve), and vice versa, at varying distances along the pipeline close to the

pumping station, the ISR would probably be (-ve) to that point, resulting in a high value

of Q, limited only by cavitation in the first Stage Pump during start-up, and a

correspondingly high power consumption.

However, when the time period of start-up operation at high flowrates is extensive, the

power consumed by the motor during this time, either must not exceed the full load

rating of the motor or at least must not exceed the allowable percentage overload and

duration limitation, specified by the manufacturers of the motor.

As the pipeline is progressively further filled with water, the ISR would normally

increase, resulting in a reduction in (Q and consumed power) to a value where the

second Stage Pump may be started.

With both first and second Stage Pumps running, Q would normally increase again but

as the pipeline is progressively further filled with water, the ISR should again increase,

resulting in a reduction in Q to a value where the third stage pump may be started. The

start-up of the fourth and any subsequent stages should follow similarly.

In order to determine the time delay required for the start-up of each successive stage, it

is first necessary to establish the start-up path that the System should follow, as thepipeline is progressively filled with water.

START-UP PATH

TYPICAL METHOD OF DETERMINATION

Certain assumptions may be made to simplify calculations but the applicability of

certain assumptions may vary from one case to another:-

Assumptions

1. Inside diameter of pipe (D) is constant throughout entire length and no restrictions

are imposed anywhere in the pipeline.



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2. Velocity head (Hvd) are small and may be neglected.

3. First stage pump is not cavitating when all stages are operating with a full

pipeline.

4. Time required for each pump to accelerate from rest to full speed is insignificant

compared with time required to fill the pipeline.

5. The pipeline is initially empty and pumping is commenced with water.

6. Allowance for efficiency of vee-belt drive = 95%.

7. Frictional resistance of stationary (idling) pumps = zero. The exact loss through

an idling pumps is around half to one velocity head. This can be included in the

analysis if desired.

8. Pipeline friction factor is constant during start-up.

9. Time to accelerate flow in pipeline may be significant.

10. Water supply to first stage pump is limited.

PROCEDURE:

PIPELINE PROFILE

The values for Rx, relative level (e.g. relative to sea level or other datum) corresponding

to progressively actual lengths, Rx, of the pipeline are graphed against actual lengths of pipelines as in Figure 8. Zx can then be calculated relative to the pump position (Ro).

Several intermediate values of Lx (e.g. 500 m, 1000 m, 1500 m, etc.) are chosen and the

corresponding values of Zx read from the plot. These sets of values are tabulated.

Figure 8: Typical Pipeline Profile

POWER CONSUMPTION (KW) CURVES

From pump performance data on clear water, at the proposed pump speed, the

power/flowrate (kW/Q) characteristics are calculated and plotted on a graph, Figure 9.



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Note that the appropriate drive efficiency is employed in the kW/Q calculation. The

maximum continuous rating motor kW is drawn also in Figure 9. The value of Q

corresponding to this rated kW is the estimated maximum flowrate, QOL, attainable

without motor overload.

NPSH LIMITATION

Values of NPSH available for the specific suction system, when handling clear water

are calculated. The values of NPSH required by the pump are obtained from the

performance curve. These 2 sets of values are plotted on a graph Figure 10, to yield the

flowrate, QNPSH above which cavitation will commence.

The value for X is also plotted on figure 9 to determine the kW consumed at X. Tests

on Warman pumps, to date, indicated that the kW consumed at values of Q in excess of

QNPSH under cavitating conditions do not exceed the value of kW at QNPSH,

enabling this value to be treated as the maximum kW consumed when cavitating.

Figure 9: Power Consumption Curves

Figure 10: Npsh Limitation



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Figure 11: Typical Start-Up And Filling Path Analysis

MULTI-STAGE PUMP H/Q CURVES

The HW /Q curves for the number of stages required are plotted on a graph, Figure 12,

showing the different HW /Q characteristics when the first stage only, first and second

stages only, etc., are operating.

The value of QOL is marked on the graph.

The value of QNPSH is marked on the graph.

Point ‘A’ is established by the empirical formulae:



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Qa = 1.20 QNPSHHa = 0.75 HWQA (from HW /Q curve where Q = QA)

The broken HW /Q Curve for cavitating conditions is constructed by departing the

HW /Q curve at Q = QNPSH, passing through Point ‘A’ then dropping sharply down toHW = zero at a value slightly in excess of QA. This method of construction is

sufficiently accurate for the purpose as in Figure 11.

VARYING SYSTEM RESISTANCE CURVES

Suitable flowrates, including at least one in excess of QNPSH, i.e. Q1, Q2, Q3 and Q4are selected and tabulated.

After applying the formula V =1273 Q

d2 (m/s)

an average value of Friction Factor, f, to apply over the range of flowrates Q1 to Q4 isdetermined.

At each of the tabulated conditions (LX, ZX) the total Head, HX, is calculated for each

of the selected flowrates, (QX = Q1, or Q2, or Q3, etc.) by formula:

HX = ZX + [8.25 x 107]f

D5 LX * QX2 (m) Equation (1)

The values of HX for each value of QX are plotted (Figure 11) to obtain the ISR curve

for each pipeline length LX. It will be noted that these curves, L1, L2, L3, etc. become

steeper as LX increases from zero to full length but the values of HX are also influenced

by the values of ZX.

PLANNING THE START-UP AND FILLING PATH

The Start-up Path originates at Q = zero. With the first stage pump only, the path

moves very rapidly along the H = zero abscissa, with Q increasing, until a value, QI, is

reached, corresponding to the cavitation condition where H = zero. Flowrate QI will be

maintained until sufficient length of pipeline has become filled with water to increase

the ISR sufficiently to reduce the flowrate. The steps in start-up are:-

• Flowrate QO (= zero) exists immediately on start-up.

• Flowrate QI exists after start-up, being limited by cavitation.• Flowrate QII exists when water has just filled pipeline length L1.

• Flowrate QIII exists when water has just filled pipeline length L2.

• Flowrate QIV exists when water has just filled pipeline length L3.

In this example, each of these flowrates, QO to QIV, represents a power consumption

less than the kW absorbed for QNPSH, which has been established to be less than the

maximum continuous rating of the motor, Figure 9.

It is apparent from Figure 11 that if the second Stage Pump were started shortly after

pipeline length L1 had been filled, the first Stage Pump would operate in cavitation for

a longer period although the power consumed by each pump would be below that forQOL.



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The second Stage Pump is started when water has just filled pipeline length L3. The

flowrate increases rapidly from QIV and to QV as the second Stage Pump quickly

accelerates to full speed and progressively reduces to the stable flowrate QVI when the

water has reached the end of the pipeline (length L4) and continues to discharge from

the end. As each of the flowrates QIV to QVI also represents a power consumption lessthan maximum continuous rating of each motor, the 2-Stage unit has been started

without exceeding the maximum continuous rating of the motors and with a minimum

period of operation of the first stage pump in cavitation.

Note: In this example:

QNPSH is given to be less than QOL, i.e. kW at QNPSH is less than kW at QOL.

However, in some cases it is possible for QNPSH to be greater than QOL which can

result in a power consumption in excess of the maximum continuous rating of the first

stage (and possibly subsequent stages). In certain cases, the excessive power

consumption may be so prolonged that higher power motors may be required simply tomeet start-up requirements.

In any case, it is necessary to determine the time periods required for the water to reach

each point in the pipeline which corresponds to the time for start-up of the relative

pump stage.

This is calculated as follows:-

The average flowrate QOL for filling the pipeline between any 2 points, e.g.

for LOL to L1: QAV =Q + Q

2

II I (L/s)

and for L1 to L2: QAV =Q + Q

2

III II (L/s) and so on.

The average value of V is calculated :- VAV =1273 Q

d

AV

2 (m/s)

the time required to fill each selected section (DL) of pipeline is calculated:-

tAV = ∆L Vav

(seconds)

Note: The times required to accelerate each pump from start-up to full speed are treated

as zero. i.e. times required to change from flowrates Qo to QI and from QIV to QV are

taken as zero.

The values of tav (seconds) are converted to minutes (Tav). The progressive sums of

the individual values to Tav are taken to establish:-

1. Time delay from start-up of first stage to start-up of each of the subsequent stages.

2. Total time to fill pipeline with water.



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The total time should be checked by the approximate formula:

TTOTAL ≅ L . D

76300 .Q + Q

2

I VI

2

(minutes)

Table 2 represents a convenient form for tabulating the calculated data.

Lx

(m)Rx

(m)Zx = Rx - Ro

(m)Ax (HLX)Qx

(m)∆L(m)

Qav

(L/s)Vav

(m/s)tav

(s)Tav

(min)Ttotal

(min)

L1 R0 Zero Zero Zero QII + Q

IF F

Q1 (HL1)Q1 L1 - L0 2 R R T1 T1

L1 R1 Z1 Q2 (HL1)Q2O O

Q3 (HL1)Q3 QIII + Q

II

M M

Q4 (HL1)Q4 L2 - L1 2 T2 (T2 + T1)

Q1 (HL2)Q1 E E

L2 R2 Z2 Q2 (HL2)Q2 QIV + QIII Q QQ3 (HL2)Q3 L3 - L2 2 U U T3 (T3 + T2 + T1)

Q4 (HL2)Q4A A

Q1 (HL3)Q1 QVI + Q

V

T T

L3 R3 Z3 Q2 (HL3)Q2 L4 - L3 2 I I T4 (T4 + T3 + T2 + T1)

Q3 (HL3)Q3O O

Q4 (HL3)Q4N N

Q1 (HL4)Q1

L4 R4 Z4 Q2 (HL4)Q2

Q3 (HL4)Q3

Q4 (HL4)Q4

EXAMPLE

A typical more complex example is illustrated and summarised in Figures 12 and 13. A

very detailed analysis was necessary in view of the wide fluctuations in ZX in the first

half of the pipeline:

Prior to any consideration of start-up and filling path, it was estimated that a 45 kW

motor was adequate for each drive for the slurry-pumping duty range.

First Stage Start-Up

However, the power consumed initially at point ‘A’ by the first stage pump unit is

nearly 60 kW for QNPSH but reduces progressively, passing through 45 kW after about

47 seconds when approximately 270 m of linear pipeline length has been filled and Q

progressively decreases.

The shut-off head of the first Stage Pump, at 1300 rpm, is 41m.

For ZX = 41 m: RX = RO + ZX = 12 + 41 = 53 m

From Figure 12, Q will progressively decrease to reach zero when around 500 linear

metres of pipeline has been filled unless the second Stage is started beforehand.



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Second Stage Start-Up

The second Stage is planned to start at point ‘B’ when at least 350 linear metres of

pipeline has been filled, in order to avoid any further overloading. Q and the power

consumed by each stage will both increase but not beyond overload conditions, to Point‘C’. Note that the detailed analysis reveals that Q fluctuates in the region between

points ‘C’ and ‘D’ due largely to respective fluctuations in Zx.

Third and Fourth Stage Start-Up

The third and fourth stages are planned to start at point ‘D’ when 1900 linear metres of

the pipeline has been filled and the values of Q and the power consumed by all 4 stages

will both increase, but not beyond overload conditions, to Point ‘E’ and thence to point

‘F’ when the pipeline has been completely filled and the flowrate is stable.

The third and fourth stages could be started in sequence, if preferred, yielding thealternative path

‘D’ – ‘X’ -– ‘Y’ – ‘F’.

Motor Size Summary

In view of the extended period of operation in excess of maximum continuous rating of

a 45 kW motor, a 60 kW rating would probably be recommended by the manufacturers

for the first stage. 45 kW rating motors would be adequate for the second, third and

fourth stages.



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Figure 12: Start-Up Path Example



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Figure 13: Start-up Path Example

START-UP ON AND FILLING THE PIPELINE WITH SLURRY

Although not normally recommended, start-up on slurry may be unavoidable in some

installations. This would require a separate analysis resulting in another graphical

presentation similar to Figure 13. Values of kW consumed would be higher than for

water, suggesting that in the above example, a motor of kW rating greater than 60 for

the first stage and possibly also the second stage would be required.



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The start-up path would have to be planned to avoid flowrates corresponding to pipeline

velocities below the Limiting Settling Velocity (VL).

START-UP AND FILLING WITH VARIABLE SPEED DRIVES

A variable speed drive on the first stage pump may be employed to limit the values of A

and kW throughout the entire start-up path. This may assist in avoiding the need for

high motor ratings, simply to cater for start-up conditions, providing that adequately

sensitive speed control can be applied.

The application of variable speed would require a separate analysis, resulting in another

graphical presentation in a form similar to Figure 13, but made more complex by reason

of the variations of H/Q characteristics with speed.

SHUT DOWN PROCEDURES








SIMPLE and CONTROLLED - as shown in Figures 6 and 7. Basic procedures aremuch the same irrespective of the type of system. Hence, while the step by step

procedures are more general in this Section, they can be utilised and applied to any

system without too much change. The degree of instrumentation and control should

only influence how the various basic procedures are carried out and not dictate any

changes to procedures.

STANDARD SHUT DOWN

Procedures for SIMPLE and CONTROLLED system shut-down are set out below as

step by step instructions. As previously discussed, each system will be somewhat

unique but procedures can be established by following the basic procedures as set out

below.

When ever possible the pipeline should be shut-down on water, or at least dilute slurry.

The time for slurry to be transported along the full length of the pipeline can be

calculated (Start-Up with Line Empty) and used to establish the time that water needs to

be fed into the pipeline to flush the line. Water can be supplied via the make-up supply.

If the pipeline is to be re-started in a short period and it is known that the pipeline can

be re-started without problems, then slurry can be left in the pipeline, saving the time

required for flushing.



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Short pipelines will normally drain back to the pumps. Hence there may be no need to

flush the pipeline with water. Either the small amount of slurry left in the line might be

simply left until the next start or the line can be drained by means of the Drain Valve.

SIMPLE SYSTEM (FIGURE 6): STANDARD SHUT-DOWN

1. Reduce slurry density gradually by introducing make-up water to flush the

pipeline.

2. As the density is reducing, the head and flowrate demand will drop. Hence one or

more stages can be stopped. Stages at the end of the train should be stopped first

working back to the first stage.

3. When the slurry density has reduced, switch off all remaining pumps.

4. Allow any runback to reduce and stop. During this period the pumps will slowlyrotate with slurry passing through them. Runback may take 10 to 30 minutes

depending upon the pipeline contour. The pumps must not be restarted while

runback is occurring.

5. Close the intake valve.

6. Open the drain valve and completely empty the pipeline, pumps and intake sump.

Alternatively, if the pipeline was flushed, the water or dilute slurry in the pumps

and pipe and sump may be left ready for the next start.

7. Turn off all gland sealing water pumps and supply.

8. If the pipeline was not flushed and the intake sump is not agitated, then drain and

flush the sump. If the intake sump is agitated, the sump can be left partially full

with the agitator turning.

9. Visually inspect all pumps and equipment to ensure all items of equipment are

turned off and ready for the next start.

CONTROLLED SYSTEM (FIGURE 7): STANDARD SHUT-DOWN

For fully automatic systems, it would only be necessary to activate the shut downprocedure. While these systems would be fitted with a controlled discharge valve, it is

not recommended that this is used to throttle the flowrate. However, a discharge valve

is useful for maintaining the pipeline filled ready for the next start. Preferably, the

pipeline should still be flushed with water or at least run for a set time with dilute

slurry. When the pipeline is shut down, the discharge valve isolates the pipeline from

the pumps. This would allow maintenance work to be carried out on the pumps while

maintaining the pipeline at the ready. This will reduce down time and provide smoother

operation.

1. Reduce slurry density gradually by introducing make-up water to flush the

pipeline.



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2. As the density is reducing, the head and flowrate demand will drop. Hence one or

more stages can be stopped. Stages at the end of the train should be stopped first

working back to the first stage. The control system can monitor changes in

density and flow, and make adjustments to the number of pumps operating or by

reducing V/S unit speed.

3. At a predetermined time for flushing, the discharge valve can be slowly closed.

4. When the discharge valve is fully shut, stop all pumps. Pumps can be stopped

one after the other quickly. Open the drain valve and allow the pumps and intake

sump to empty. Make-up water can be run to flush the sump and pumps.

Alternate 1: After the discharge valve is shut, the intake valve can be shut to drain

the pumps without empty the intake sump. The intake sump agitator should be

left operating if any slurry remains in the sump.

Alternate 2: If the pipeline was flushed, it is possible to leave water or dilute

slurry in the pumps and sump. The system would then be ready for an immediate

start. The drain valve need not be opened in this case. This is the preferred

method to shut down the pumps and pipeline. The pumps are primed ready to go

and the pipeline is full.

5. Turn off all gland sealing water pumps and supply.

6. Close the intake valve. Note that the GSW pumps should be shut down before

shutting the intake valve. If the GSW pumps are ON then the normally low

pressure intake valve will be pressurised by the high pressure GSW.

7. Check all controls have returned to normal. Visually inspect all pumps and

equipment to ensure all items of equipment are turned off and ready for the next

start.

EMERGENCY SHUT DOWN

This type of shut-down is forced usually by a complete power failure. Far less likely

would be a major bursting of the pipeline and a loss of head resulting in increased

flowrate from the pumps. Typically, the power draw would rapidly increase and theelectrical controllers would cause all or most pumps to trip from over current.

There is little that can be done in either of the above cases for a SIMPLE or

CONTROLLED system. If all power fails, then the gland water pumps will also stop.

Before pumps are restarted, it is recommended that the gland packings be inspected and

possibly replaced as slurry will enter the glands with no GSW. If the pumps stop but

the GSW pumps continue to operate, then there probably will be minimum effects on

the glands.

For systems fitted with an automatic opening dump valve, this would activate and dump

some of the pipeline contents. Runback and major flooding of the pump and sumpcould thereby be minimised. Slow acting non-return valves, if fitted, would also

minimise runback effects.



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Intake sumps could be sized with reserve capacity to take the runback in emergencies.

SINGLE PUMPS SPACED ALONG THE LINE - OPERATION FIGURES

14, 15, 16 AND 17

HOPPER FED BOOSTING PUMPS

Figures 14 and 15 depict an arrangement where a long-distance and/or a high static head

pumping duty is handled by a number of fixed-speed, hopper-fed, single pump units,

each handling a Hm /Q duty with the capability of a single centrifugal pump.

Figure 14: Hopper Fed - Essentially Horizontal Route

Figure 15: Hopper Fed - Essentially Rising Route



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Theoretically, if each pump were correctly speeded for its actual duty, this approach

should prove satisfactory. However, in practice, it has been found that, as actual wear

rates vary amongst identical pumps, the Hm /Q characteristics of each pump vary

differently with progressive wear.

e.g. If Pump Nº 2 wore more rapidly than Nº 1, the flowrate from Pump Nº 2 would

reduce, the level in Nº 2 hopper would rise and spillage would occur. This could result

in an inadequate velocity in the discharge pipeline from Pump Nº 2 with probable

settling of solids and blockage. The entire flow into Nº 2 hopper would then overflow

as spillage.

Disadvantages and advantages of this arrangement are summarised in Filling the

Discharge Pipe.

PRESSURE BOOSTING PUMPS

Figures 16 and 17 depict an alternative arrangement consisting of a number of single

pumps, spaced at intervals along the pipeline route and each acting as an in-line

pressure booster.

It is theoretically possible to locate each pump such that, under normal stable operating

conditions, the intake head at each pump is close to atmospheric pressure, and the

discharge head is approximately Hm, apparently enabling relatively low-pressure

pipework and pump casings (and possibly centrifugally-sealed pumps) to be employed.

However, it would also be necessary to start each pump in sequence with very carefully-

controlled low flowrates to avoid exceeding normal stable maximum operatingpressures throughout the system. It is not generally practical for these conditions to be

met.

If the pumps were started in sequence, with water, or slurry, being fed into an empty

pipeline, the initial flowrate from the 1st stage could be well in excess of the normal,

due to the initially-low system resistance. The high momentum of the long cylinder

or slug of liquid arriving at the next pump has been demonstrated to generate

sufficient hydraulic shock to burst the centrifugal-seal, the pump casing and/or

pipeline and couplings. In other cases the pump house or pump skid have been

know to bodily move with the momentum and forces of the slurry suddenly

hammering into the next pump stage.

When high static discharge heads exist, abnormally-high pressures would be

experienced at the lower levels of the pipeline immediately following shut-down.

A further disadvantage of this arrangement is that the failure (e.g. due to wear) of one of

the pumps to develop sufficient head my result in a negative (-ve) suction head at, and

cavitation of, the pumps downstream. This would result in insufficient head being

developed to maintain an adequate flowrate in the system, probably resulting in a

pipeline blockage.

Disadvantages and advantages of the various arrangements are summarised in Fillingthe Discharge Pipe.



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Figure 16: Pressure Boosting - Essentially Horizontal Route

Figure 17: Pressure Boosting - Essentially Rising Route

warman multi-stage pumping systems jun97

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