plsy project pumps

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THE UNI

I n s t r u c t o r : M r . A p h t a a b M o h a m m e d

2011Date: Monday 6th June

PLANT SYSTEMS AND

SERVICES-PLSY 210D

PROJECT

PUMPSPrepared by:

Aliya Cummings-McKie-111004688

Lemuel Abdullah-111004426

Rochelle Antoine-111005005

THE UNIVERSITY OF TRINIDAD AND TOBAGO

(JOHN S. DONALDSON TECHNICAL INSTITUTE CAMPUS)


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TABLE OF CONTENTS

title

1. introduction to pumps 3

What is a pump? 3 Applications involved 3

2. pump application, selection and code requirements 12

Pump Applications 12 Pump Selection 21 Code requirements for boiler feed water pumps 21

3.pump installation and maintenance 22

Introduction 22 Installation 22 Start-up 24 Maintenance 25

4. pump operations and drivers 26 Pump Operations 26 Caution 29 Pump Drives 30

5. pump seals and bearings 33

Introduction 33 Pump Shaft Sealing 33 Bearings 37


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INTRODUCTION TO PUMPS

At the beginning of the industrial age, a very crude form of the pump had surfaced. It was one of the

first pieces of powered machinery to be developed at this time. The pump has evolved into a variety of

types, sizes and applications. Familiarity with the diversity of pumps in existence is compulsory as plant

operators are required to safely operate pumps during the course of their daily routines.

WHAT IS A PUMP?

A pump is defined as a mechanism used to transfer liquid from place to another by imparting energy to

the liquid being transferred.

Applications involved

A pump has many uses. Therefore, a car may have many types of pumps for different tasks. The

following are tasks that each requires a different pump:

Pumping lubricating oil Pumping fuel Pumping engine coolant Pumping high pressure hydraulic fluid for power steering Hydraulic pump attached to a foot pedal, activating the brakes.

Pumps are used to move materials ranging from high temperature molten metals to low temperature

cryogenic materials. They are also used to generate unrecognizably small pressures, to pressures high

enough to cause liquids to become corrosive. Pumps are also designed to supply a wide range of

quantities from one drop per day, to 4,000,000,000 liters per day. The power requirement of pumps

ranges from a few watts to nearly 75 Megawatts.


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Common Types of Pumps Required in Industrial Plants

Boiler Feed Water Pump

This pump supplies the boiler with feed water and must be capable of forcing this feed water into the

boiler against the existing pressure in the boiler.

Fuel Oil Pump

This pump is used in oil fired boilers to pump fuel into burners.

Lubricating Oil Pump

This pump circulates the oil to the bearings of a machine, such as a turbine, engine, pump or

compressor.

Circulating Water Pump (Cooling Water Pump)

It pumps water through a heat exchanger, that is, a condenser or a heater.

Chemical Feed Pump

These are small capacity units that pump chemicals into boilers, whereas, larger units are used as

process pumps.

Fire Pump

This pump provides water to plant fire lines.

Domestic Water Pump

This pump supplies water to plant washrooms, etc.

Pump Location

Pumps are typically secured to stable locations and are small enough to be suspended by pipework. For

vibration and stability control, strengthened concrete foundations support large pumps. Pumps are

normally located to accommodate easy access for operation and maintenance. They can be placed at

lake bottoms, down a well or inside a pipeline or vessel.


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Pump Drivers

Source of Power: electric motor, a gas or diesel internal combustion engine, a gas, water or steam

turbine, a steam engine or steam operated piston.

Operation of Pumps: hand or foot (manual), by air pressure or other fluid pressure, or an

electromagnet.

Classification of Pumps:

Pumps have two main groupings:

Pumps that rely on velocity to create pressure. Pumps that rely on positive displacement to create pressure.

Therefore, pumps are classified depending on their method of operation: reciprocating, centrifugal, or

rotary.

Reciprocating Pumps

These are positive displacement pumps that use the reciprocating motion of pistons, plungers or

diaphragms to move the liquid through the pump. They are used for low volume, high temperature

applications such as chemical feeding, which uses small, high pressure boiler feed pumps and fuel oil

pumps. Their discharge is in pulses instead of a smooth liquid flow.

Figure 1- Sketch of a Plunger Pump


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Figure 2-Avertical piston reciprocating pump

Figure 3-Mechanically Activated Diaphragm Pump

Centrifugal Pumps

These can be defined as pumps using centrifugal force to develop velocity in the liquid being handled.

Velocity is converted to pressure when liquid velocity decreases. When kinetic energy decreases,pressure increases. Centrifugal pumps are divided into the following types: volute, diffuser, axial flow,

mixed flow and regenerative (considered in this classification).

Volute Centrifugal Pump

Liquid is drawn into the impellers eye and discharged from the impeller periphery into the volute

casing, which increases in cross-sectional area when approaching the pump discharge. In this area, the


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liquid discharge velocity from the impeller is lowered and converted to pressure. For a more effective

conversion form velocity to pressure, stationary diffuser vanes can be installed around the impeller rim.

The new configuration indicates the term diffuser centrifugal pump.

The combination of centrifugal force and pressure that is created by velocity decrease, accounts for the

total pressure developed by the volute or diffuser pumps.

Axial Flow Pump (Propeller Pump)

The title of this pump is self-descriptive since the liquid flow direction is along the axis of the shaft,

instead of radiating away from the shaft. This pump also uses impeller with blades similar to aircraft

propeller blades (hence the name: Propeller Pump). In this pump, pressure is developed by the

propelling or lifting action of the blades. The pump is also used for large volumes and low to

intermediate pressures.


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Figure 4-Vertical Axial Flow Pump

Mixed Flow Pump

This pump combines some characteristic of axial, volute, and diffuser flow pumps. Pressure is

developed by partial centrifugal force and by partial propelling action of the impeller. This pump is used

for high capacity, low pressure applications.

Figure 5-Mixed Flow pump


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Regenerative (or Turbine) Pump

Liquid enters the pump suction and circulates almost 360 by impeller to pump discharge. Impeller

vanes travel through channel in pump casing. Liquid receives continuous impulses from fast moving

vanes and pressure increases substantially as the liquid approaches the pump discharge. With this

pump, pressure can be developed several times more than would be developed form a centrifugal pumpof similar size and speed.

Figure 6- Regenerative and Turbine Pump in comparison to a Volute Centrifugal Pump

Note: In this introduction, the discharge from pumps is referred to as pressure. After this introduction,

it would be referred to as head, meaning differential pressure between pump intake and pump

discharge. For producing high head, discharge from one impeller must be directed to the intake of

another impeller. This is known as staging. A pump with three stages is called a 3-stage pump. Staging

is used for increased differential pressure, where more stages means more pressure.

Rotary Pumps

These are positive displacement pumps where pockets of liquid are transferred from the low pressure

side to the high pressure side, where they are forced to empty themselves and return to the low

pressure side for refilling. These pumps have a lower capacity than centrifugal pumps. Common rotary

pumps include gear pumps, lobe pumps and sliding vane pumps.


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Gear Pumps (External or Spur Gear Pumps)

These consist of housing, driving gear and an idler gear. The gears rotate in opposite directions,

transporting pockets of liquid to the pump discharge. After meshing of gear teeth, liquid is released

from the pockets, as liquid and gear tooth cannot occupy the pocket at the same time. Further gear

rotation causes the teeth to unmesh at the pump suction. Liquid flows in, filling the void created as thegear teeth leave the pockets.

Figure 7-Gear Pump

Lobe Pumps

These are similar to gear pumps (theoretically), since liquid is transferred around the outsides of the

rotating lobes and expelled by the lobes meshing. The difference is that lobes are both driven by

external gears which keep the lobes synchronized.

Figure 8-Lobe Pump

Sliding Vane Pumps

These pumps consist of rotor, sliding vanes held in rotor and eccentric casing. Rotor causes vanes to

rotate and vanes slide in and out to conform to the pump casings changing proximity. Pockets of liquid

are transferred between vanes. Vanes are forced to retract by diminishing clearance external of the


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pump casing; pocket size decreases and liquid is forced out. When the vanes rotate past minimum

clearance external of pump casing, pocket size increase and liquid on the pumps intake side flows in,

filling the increasing void.

Figure 9-Sliding Vane Pump

Rotary pumps deliver high pump pressure liquid with the pulsations common to reciprocating pumps. A

means of pressure relief should be installed in the discharge line before the discharge valve, where

positive displacement pumps are installed. If the discharge valve is unintentionally closed, excessively

high pressures can be produced, causing damage to the pump or piping.


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PUMP APPLICATION, Selection and code requirements

Pump applications

Some pump applications in plants are:

Boiler Circulating Pumps Feed water Pumps Fuel Oil Pumps Chemical Feed Pumps Condensate Pumps Circulating Water Pumps Vacuum Pumps

In this module, these applications will be briefly discussed.

BOILER CIRCULATING PUMPS

Two types of boiler circulating pumps that are commonly used are:

1. Conventional Drive Type:In this type of pump, an electric motor is usually used but steam turbines can also be used. The

driver is connected to the pump shaft by a flexible coupling and the pump itself may be a single-

stage or two-stage volute type centrifugal pump.

Volute pump centrifugal pump housed in a spiral casing.

In the application of this type of pump in industry, when temperatures and pressures are not

excessively high, the pump shaft is sealed using a packing gland or mechanical seal. When the

temperatures and pressures are higher, a special type of shaft seal is used where a water labyrinth is

employed between a throttling bushing and the soft packing.

JUST SO YOU KNOW:

The sealing water for this labyrinth however cannot be taken from the pump casing because the

high temperature water would flash in the seal and result in erosion. For this reason, cooler high-

pressure injection water is taken from the boiler feed pump discharge before the final feed water

heaters when the water is at a temperature and pressure suitable for the seal.

2. Submerged Motor Type:This type of pump has two designs: -

- Wet Type, &- Canned Motor Type


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Wet Type

In this type of pump, the motor is housed in the same casing as the propellers of the pump. The

liquid being pumped surrounds and comes into contact with the stator, rotor and bearings. For the

windings, waterproof insulation made usually of PVC (polyvinyl chloride) us used.

Canned Motor Type

In this type of pump, the liquid being pumped is allowed to enter the motor casing but it does not

come into contact with the stator and rotor as it is prevented by means of cans or sealing jackets. By

means of an auxiliary impeller on the motor shaft, high pressure cooling water is circulated in the

space between the stator and rotor cans. This water (at high pressure) is then cooled by lowpressure cooling water via passage through an external cooler.

In the submerged motor type pump, a thermal barrier is required to hinder the flow of heat from

the water being pumped, into the part of the pump where the motor is housed. The barrier consists

of a close fitting sleeve and bushing with an extended surface and is located immediately above the

main impeller.


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BOILER FEEDWATER PUMPS

On a general basis, feed water pumps are either centrifugal or reciprocating. The centrifugal is the more

commonly used of the two and they type of pump chosen for this service depends largely on thecapacity and pressure of the boiler.

Centrifugal Feed water Pumps

These types of pumps are used in medium and large-sized plants. Two different pumps called the volute

pump and diffuser pump may be used which may be of the split case or barrel type design.

This particular horizontal volute double-suction split case pump has a maximum operating pressure of

2.5MPa.

The pump shown above is a multi-stage diffuser barrel pump. The cartridge-style inner case sub-

assembly includes the rotor, discharge head, suction head and bearing assembly. The cartridge typeconstruction allows for the entire assembly to be removed as a single unit to facilitate maintenance

without disturbing the driver or piping.

For the purpose of providing allowance for unequal expansion between the inner and outer casings, the

inner casing is secured to only one end of the barrel.


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Reciprocating Feed Water Pumps

Reciprocating pumps can be of the direct steam-driven type or the power driven type.

Direct Steam-Driven can be either vertical or horizontal in configuration. A unique advantage of this type

of pump is that its capacity can be varied from zero to maximum independent of the discharge pressure

and the reverse is also true. This type of pump however, is limited to pressures less than 2750kPa and a

capacity of 10,000kg/h.

Power Driven Reciprocating Pumps may be used to supply feed water to a de-superheater in high

pressure plants.

JUST SO YOU KNOW: A desuperheating is the process by which superheated steam is restored to its

saturated state, or the superheat temperature is reduced.

Pump Power Driven Pumps Direct Steam-Driven Pumps

Attributes

1. Costs more than directsteam driven type

1. High reliability2. More compact than

horizontal steam pumps

2. Low maintenance costs

3. Less economical thanpower driven types if the

exhaust steam cannot be

used for feed heating or

process

Direct Acting Steam Driven Pump Power-driven Single-action Reciprocating Pump

Reciprocating pumps are subject however, to increased wear on valves, seats, cylinders and pistons

when used for high temperature and pressure services.


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A multistage pump is shown above.

CONDENSATE PUMPS

These pumps are used in plants which produce low pressure steam which is used to heat buildings.

In plants that supply high pressure steam to condensing turbines, the pump that carries the condensate

to the condenser must be of a special design. This pump, known as the condensate or extraction pump

must be designed having a low suction head requirement, as it usually discharges through low pressure

heaters to a de-aerator.

Why?: This is so because the turbine is usually located in the basement of the plant and the condensate

pump cannot be supplied with much suction head without raising the condenser or installing the pump

in a pit.

Centrifugal pumps of either a horizontal or vertical configuration may be used for this type of service.

Vertical is favored over horizontal as it can be set up in a pit in the basement floor to attain a few metres

of (suction) head. To reduce the possibility of the condensate flashing or causing cavitation because it is


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near flashing temperature, the pumps first stage impeller is designed with a large inlet or eye. To avoid

cavitation, the shaft glands of this pump must be water sealed so that no air gets into the pump.

In conjunction with centrifugal pumps which are most frequently used for this type of service, there are

some rotary, regenerative and reciprocating designs that may also be used.

Condensate pump

CIRCULATING WATER PUMPS

This type of pump is required to move large quantities of cooling water through turbine condensers and

can be either vertical or horizontal configuration.

Generally, these are low head large volume pumps featuring low speeds and single stage design.

Of the vertical configuration, some types that are favored are:

Volute Type Propeller type Mixed Flow Type

For a horizontal configuration, a volute centrifugal pump that employs either a single or double inlet is

used.

It is also a frequent practice to use two 50% capacity pumps for circulating water service. In some cases

it would be more economical to run just one pump instead of both and sometimes running only one

pump is sufficient, even at full load.


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MISCELLANEOUS PUMPS

Include:

Fuel Oil Pumps Chemical pumps Vacuum Pumps & Ash Handling Pumps

Fuel Oil Pumps

Type: Usually some sort of ROTARY POSITIVE DISPLACEMENT pump.

Use: A means of loading/unloading, transfer and circulating fuel oil.

Capacity: 0.23 230+ m3/h

Requirements: In the effect that flow is restricted, a relief or bypass is needed to protect the pump and

discharge lines from excessive pressure.

Other types of pumps used in this service: Direct acting steam-driven pumps are sometimes used in

smaller plants, whereas, in larger stations centrifugal fuel oil pumps may be used.


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Chemical Feed Pumps

Type: Usually the motor-driven, reciprocating plunger type.

Capacity: Can be varied by adjusting the stroke of the pump, and in this way the amount of chemical fed

to the boiler can be closely controlled.

Requirements: This type of pump should be equipped with a relied valve on the discharge in order to

avoid damage from over pressure.

Material of Construction: Chemical feed pump materials will be selected based on specific application

requirements.


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Vacuum Pumps

Type: May be the positive displacement type or the jet type.

Use: Can be sued to remove air and non-condensable gases from the turbine condenser.

Operating Medium: For the jet pump, this is a jet of high pressure steam which may be applied to two or

three stages in order to compress the air and gas from the condenser pressure to atmosphere.

The positive displacement type may use a reciprocating piston or may feature a rotor with lobes or veins

in its design.

Vacuum Pump

Ash Handling Pumps

Type: Usually single stage centrifugal pumps using flat bladed impellers.

Use: To pump ash laden water.

Material of Construction: Wear resistant alloy.

JUST SO YOU KNOW: Sump pumps are also used in plant for sump and sewage lift pumps.

Progressive Cavity Pumps are also used for high viscosity material.


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Ash Handling Pump


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PUMP SELECTION

By considering capacity, head, pump characteristics required and fluid to be pumped, the type of pump

to be used can be decided.

Pump Centrifugal Pumps Rotary Pumps Reciprocating Pumps

Attributes

Good for a widerange of

capacities (from

small to largest

available)

Will pumpagainst high

discharge heads

Will handledirty or abrasivefluids and fluids

with high solid

content well

Not positivedisplacement

pumps so

discharge flow

will decrease

with increase in

discharge head

and vice versa

Limited to fairlysmall capacities

Will pumpagainst high

heads

Will handleheavy or

viscous fluids

Positivedisplacement

pumps, so their

dischargecapacity

remains

constant

regardless of

how the

discharge head

may vary

Will not handleabrasive fluids

with suffering

severe erosion

Deal withrelatively small

capacities

Capable ofproducing the

highest

discharge heads

Cansatisfactorily

handle only

clean and clear

liquids Discharge flow

is pulsating and

not continuous

Positivedisplacement

pumps so the

discharge

capacity

remains

constant as long

as the pumpspeed remains

the same

The layout for the piping system should be carefully studied so that the pump capacity required and the

head conditions under which the pump must work can be determined.

A clear understanding of the full range of conditions under which the pump is expected to operate

should be given to all prospective pump suppliers and any deviation from the stated performance and

actual performance should have monetary penalty provided in the tender documents.

CODE REQUIREMENTS FOR BOILER FEED WATER PUMPS

The most common arrangement in industry and on power plants is to use two centrifugal pumps, each

of which are capable of supplying the boilers with the full requirement of feed water. So, while one

pump is in operation, the other is on standby.


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pump installation and maintenance

introduction

Installation of the pump is important to ensure satisfactory operation

Unit should be located where it is easily accessible for inspection and repair Sufficient headroom should be provided for removal of casing and rotor.

Installation

Piping

Piping should be supported independently from the pump This would avoid strain on the casing The pump must be filled before starting Force on the pump casing causes distortion and can lead to internal misalignment in the pump Expansion joints which provide flexibility are used in the piping.

Figure 1- Installing piping for pumps

Valves

Valves are very important in pumps e.g. if a pump is to work on a suction lift, then a foot valve should be

installed in the suction line.

Figure 2-Foot valve


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Gate and check valves should be installed in the discharge line close to the pump with the check valve

between the gate valve and pump e.g. check valves are used in diaphragm pumps and relief valves are

used in positive displacement types.

Figure 3-Relief Valve

Thrust Blocks

These are used to support the piping systems at junctions or turns in the pipe Provides strong anchor points when there are catastrophic failure It normally is design to handle maximum reactionary forces.


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Foundations

Should have sufficient mass to absorb vibration and to provide adequate support for the pumpbase plate.

Small pumps usually are put up top of a concrete foundation while larger pumps are placedseparately on supported blocks which may require pilings deep into the ground.

If pumps that are going to be installed, you should ensure proper alignment and installation.Alignment

There are two types of alignment:

Angular Offset or Axial

A check for angular alignment is made by inserting a taper or feeler gauge between the couplingfaces at 4 points spaced at 90 degree intervals.

Axial alignment is checked by placing a straight edge across both coupling rims at the top,bottom and sides.

An accurate method for alignment is the use of a dial gauge. With heavy machines precise positioning is difficult When alignment is finished, it is important that it is checked again after the piping has been

connected

Alignment should also be checked after repairs, new installations, or even earthquakes.Start up

Before pump is started for the first time, it is important to check if it rotates in proper direction This should be done with shaft coupling disconnected Motor side of the coupling should be secure so it would not flop around during rotation check Stuffing box should be inspected before start-up If stuffing box is not already packed, it should be cleaned and packed. Sleeve bearings should be cleaned thoroughly before starting the pump and should be filled

with proper lubricant to avoid friction and roughness

Sometimes sleeve bearings run too hot on the start-up Unit should be stopped and allow to cool down The first start maybe for only a few minutes Centrifugal pumps must be primed before starting. If there is a foot valve in the pumps, then an exhauster is not required The use of a vacuum pump is another method of priming It is important that in a centrifugal pump, the casing and suction are filled with liquid before

started.


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Figure 5- Centrifugal Pump

Maintenance

Maintenance is important for greater life-span For reciprocating pumps only spare valves and packing on hand is necessary For centrifugal pumps bearings, shaft sleeves; wearing rings and supply of packing is necessary. Spare parts should always be kept on hand Pump size, serial number and type should be given to the manufacturer when ordering spare

parts.

It is important that all maintenance be recorded

To avoid pump outages, a schedule of preventive maintenance should be set up.


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PUMP OPERATIONS

Priming a pump simply refers to filling the pump casing and suction line with water or whatever fluid is

being pumped.

A centrifugal pump must be primed before start up or a number of mishaps can occur. Cavitation can

result because the impeller will be churning air and wont produce any suction, the wearing rings may

seize because theres no liquid to lubricate them. Also, if the pump is equipped with mechanical seals or

packing, they will suffer from dry running.

METHODS OF PRIMING

If the pump is located below the source of supply:

Close the discharge valve and open the suction valve. Open the air vent valves to allow any air in the pump casing to escape. When water flows from the vents they can be closed.

The pump is now primed and ready to be started.

If the pump is located above the source of supply:

Various methods of priming can be used and in each method, a foot valve is used in the pumpsuction line.

Foot valve flap type valve which allows water to enter the suction line but prevents it from flowing

back out (of the suction line).

Priming from an external source:

Discharge valve is closed and external supply valve is opened. Vent valves are also open. Water flows into the pump where it is prevented from flowing back out by the foot valve. Water then fills the suction line and casing.

When water flows through the vent valves, the vent valves and the external supply valve are closed.

The pump is now primed and ready to be started.


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Priming from the Pump Discharge Line:

Discharge valve is shut. Priming valve and air vents are opened. Water from the discharge line fills the pump casing and suction line. When water flows through the vent valves, the vent valves and priming valve are closed.The pump is now primed and ready to be started.

Priming from a hand operated pump:

The pumps main discharge valve is shut. Priming valve is opened. The pump is operating and air is released from the pump casing and suction line, this causes water

to fill them.

When water flows from the priming pump discharge, the priming valve is shut.The main pump is now primed and ready to be started.

JUST SO YOU KNOW:

Rotary and reciprocating pumps, although they achieve better lift if they are primed before started, are

still likely to prime themselves when started. In the case of high pressure or diaphragm pumps however,

they may need to be primed as air may be compressed and not pushed out of the cylinder. This may

lead to the air expanding on the reverse stroke and this can result in the inlet of liquid being blocked.

Precautions should be taken to ensure that air does not enter a pump because it is possible for a pump

to lose its prime if air gets into the pump casing while it is in operation and this can seriously damage the

pump.


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GENERAL START-UP PROCEDURE FOR CENTRIFUGAL PUMPS

1. Turn the pump over by hand to be sure it turns freely.2. Check the oil level in the bearing houses if the pump is equipped with oil lubrication.3. Turn on the cooling water for pump bearings, stuffing boxes, and mechanical seals, if these parts are

water cooled.

NOTE*:If the cooling water supply comes from the pump itself and the pump has a suction lift, leave

the cooling water valves closed until the pump is pumping water.

4. Open the suction valve.*** Most centrifugal pumps are started with the discharge valve closed.***

5. Be sure the pump is primed.6. Close all vents and drains.7. Warn anyone in the area that may be affected, start the pump, and let it come up to speed.8. Slowly open the discharge valve.9. Check for proper flow from the stuffing boxes and adjust if necessary.10.

Check that the oiler rings are turning properly, if the bearings use this system.

11.Listen for noise or any uncommon vibration.12.Check the discharge and suction pressures.13.Check the ammeter, if one is fitted; to see if the current being drawn is normal.14.Check the flow meter, if one is fitted, to be sure that the pump is producing.15.Recheck the pump after a short run period to ensure that the glands and bearings are running cool

enough.

If and/or when a new pump is started or a pump has been down for maintenance, the following points

should be checked:

1. A complete visual inspection should be carried out for:a. Maintenance tagsb. Rags and stray toolsc. Protective Guardsd. Proper Assembly

2. Proper direction of rotation of the motor.3. Proper alignment when the pump is cold, and checked again after the pump and motor has warmed

up.

GENERAL SHUT-DOWN PROCEDURE FOR CENTRIFUGAL PUMPS

1. Close the discharge valve slowly.2. Stop the pump driver.3. Watch that the pump comes to a smooth, rolling stop.4. Shut off the cooling water.5. Close the suction valve.


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CAPACITY REGULATION OF PUMPS

Reciprocating and rotary pumps are under the classification of positive displacement pumps, and their

capacity can be regulated by varying their speed. Some reciprocating and diaphragm pumps have an

adjustable stroke length to vary the output.

Positive displacement pumps at constant speed, a specific amount of liquid is moved (discharge flow is

constant) regardless of the pump head.

Centrifugal pumps however are not positive displacement pumps, thus, the capacity changes when the

head is changed. Head increases, capacity decreases; Head decreases, capacity increases. If the head is

increased to the point where it exceeds pump design head, output drops to zero. The capacity of this

pump can be varied with the use of a pump driver (steam turbine, internal combustion engine, etc.)

which varies the speed. This pump can be driven by an electric motor (constant speed driver) or variable

speed clutch.

These pumps should always be started with the discharge valve wide open.

CAUTION

1. NEVER run a centrifugal pump continuously with the discharge valve completely closed. The frictioncaused by the trapped water churning about in the casing can cause overheating of the water to the

point where it becomes steam and causes serious damage to the pump.

2. ALWAYS operate a centrifugal pump with its suction valve wide open and NEVER use it for thepurpose of flow control. Closing or throttling this valve can damage mechanical seals and stuffing

boxes and well as cause cavitation and excessive vibrations, which may ruin the pump.

CENTRIFUGAL PUMP MINIMUM FLOW

The difference of the input power (shaft or brake power) and the useful power performed by the pump

(liquid or water power) is converted into heat. This temperature rise, due to the heating up of the water

in the pump, occurs at low temperatures and occurs very rapidly.

A recirculation line from the pump discharge to the suction source is used to prevent this rapid rise in

temperature at low flows. This line employs an orifice designed to pass the minimum flow required to

prevent overheating of the pump. The valves in this line may be operated manually or automatically but

they MUST be open on start up and shut down of the pump when it is operating at low flows.


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PUMP DRIVES

Some examples of pump drives were mentioned above. A pump can be driven by any prime mover but

the most common of these is the electric motor. Some other types of drivers are:

- Steam turbines, favored under certain conditions.- Steam Engines, Internal Combustion Engines, Gas Turbines, occasionally used for a power plant

pump.

ELECTRIC MOTORS

These are:

1. Constant Speed Induction Motor simplest arrangement for a pump driver; connected directly tothe pump. Can be used with centrifugal, rotary or reciprocating pumps.

2. Synchronous Motor More efficient than the induction motor and can be used to improve plantpower factor.

3. Wound Rotor Induction Motor Often used for pumps which are required to operate periodically atreduced output only. Has the advantage of controlling pump output by variation of the speed.

STEAM TURBINES


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This driver is usually used to drive a centrifugal pump, but can be used for rotary and reciprocating

pumps as well. This driver has the advantage of providing simple speed control and the exhaust steam

can be used for feed water heating or process.

STEAM ENGINES, INTERNAL COMBUSTION ENGINES, GAS TURBINES

Direct acting steam pumps are the only steam engine driven pumps that are known about and are used

for fuel oil service, feed water service, etc in some plants. On the other hand, internal combustion

engines are frequently used as portable and emergency fire pumps and gas turbines are becoming

popular for a variety of pump driving services. These include petroleum pipeline pumping and though

seldom, are used for auxiliary power plant pumps.

Steam Engine driven pump Internal Combustion Engine driven Pump

Gas Turbine driven Pump

JUST SO YOU KNOW: some pumps are fitted with dual drive systems in case of power failure where one

end of the pump shaft is coupled to an electric motor and the other to an internal combustion engine.

The coupling between the engine and the pump is called a centrifugal type clutch. A variation of this

system is the magnetic clutch which can be disengaged without first stopping the engine.


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PUMP WARM-UP PROCEDURE

If the proper procedure is not carried out when warming up a pump, as in the case of boiler feed pumps

and other pumps, temperature gradients will be present in the pump. This can lead to rotor distortion,

thus proper warm up is vital.

So, to avoid these temperature gradients, warm-up water that is bled off from an intermediate stage of

the boiler in service enters the bottom of the standby pump casing and leaves through the suction

nozzle.

JUST SO YOU KNOW: Standby pumps do require attention from the operator too, because large pumps

on hot standby if left in the same position for too long can start to sag at high stress points. Standby

pumps should be rolled over and brought to rest in a new position by hand ever so often. If an

antifriction bearing stays in the same position for too long the lubricant can be displaced from the rolling

surfaces and this can result in metal-metal contact. Lastly, if the foundation of a pump is subject to any

type of vibration, particularly if it is consistent, the balls (or rollers) tend to wear away small pockets in

the bearing races. This process is known as brinelling, which will eventually cause bearing failure.


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PUMP SEALS AND BEARINGS

Introduction

Power is delivered to a pump shaft to cause pumping action. During this action, liquid pumped must be

prevented from leaking out of the pump and air must be prevented from entering. A dynamic seal mustbe used for the flow prevention. Hence, it must allow turning or reciprocation of the pump shaft

without allowing uncontrolled loss of liquid.

Pump shaft sealing

Casing, stuffing boxes and mechanical shafts are employed to minimize leakage around the pump shaft.

Stuffing Boxes the bottom or inside end formed by pump casing or bottom brushing.

Comprises of a cylindrical recess around the pump shaft that holds a number of packing rings. Has a packing made from soft, durable material that bears against the pump shaft and stuffing

box walls and reduces leakage around the shaft. The packing can be made from nylon, Teflon,

copper, lead, asbestos and aluminium. The material can also include lubricating material such

as graphite or grease. Packing is held in place by a gland.

Figure 1- Stuffing Box and Packing

The gland holds the packing in place. It can be adjusted by tightening nuts or compressing ringsuntil the desired fit is obtained. It must only be tightened enough to allow a small amount of

leakage, which is needed along the shaft to lubricate and cool the packing. Also, friction

between packing and shaft is prevented, since extremely tight packing creates a friction, by

which the shaft turns against the packing, causing them both to heat up. If neglected, friction

can cause gouging of the shaft and the packing to smoke.

Pump operation with negative suction pressure causes a fully-packed stuffing box to provideimproper sealing, since air will be drawn into the casing along the shaft, stopping the required

leakage of the liquid. For proper sealing, the stuffing box is fitted with a lantern ring and a

sealing water connection.


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Lantern ring (seal cage) is a metal ring with inner and outer channels, giving it a modified Hcross section. The channels are connected by radially drilled holes. The lantern rings purpose is

to distribute sealing liquid under pressure to the packing, preventing air infiltration and

providing lubrication. The sealing liquid is provided by the pump casings high pressure section

through and external connection or an internally drilled passage in the casing. Lantern rings are

also used on pumps that handle liquid containing sand, grit or other abrasives that could

damage the shaft and shorten the life of the packing, when they enter the stuffing box. Clean

liquid provided by a separate source or the pumps discharge side via a filter/separator, keeps

the gritty substances out of the stuffing box.

Shaft Sleeves

These are subjected to corrosion, erosion, and wear at stuffing boxes. This affects their strengthas well as effective sealing with packing rings (it becomes difficult).

From smaller pumps, materials used for making shafts are corrosion and wear-resistant. Largerpump shafts are protected by renewable sleeves. The sleeves are secured on the shaft by the

shaft nut and a key prevents shaft rotation.

Figure 2- Internal part of pump with shaft sleeve

Mechanical Seals

Leakage from stuffing boxes is objectionable on pumps that handle liquids like ammonia, gasoline

and acids. The pumps are equipped with mechanical seals instead and leakage is reduced to a

minute amount. Mechanical seals are also used on pumps like high pressure pumps, where stuffing

boxes provide inadequate leak protection.


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Advantages of Mechanical Seals over Packing Rings:

Much less maintenance is required. Shafts or shaft sleeves are not used. Leakage is reduced to a minimum. Their design temperatures and pressures are high.Disadvantages of Mechanical Seals over Packing Rings or Stuffing Box

Greater first cost. Upon failure, pump is also taken out of service for longer period for replacement of seal.Generally, the mechanical seal comprises of two flat rings, each with sealing surface. Rings are

perpendicular to pump shaft, sealing faces rotate on each other. The sealing ring is held in position

by a spring. The mating ring has its face in contact with sealing rings face.

1. Rotating Mechanical Seal

Mating ring held stationary in a recessed part of the pump housing or the seal housing cover. O-ring provides a seal between ring and casing to prevent leakage. Shell (secured to the shaft by set screws) holds the sealing ring so that it turns with the shaft. A second O-ring prevents leakage between the shaft and sealing ring. When the pump shaft turns, the sealing ring is held against the mating ring by many small

springs contained in the shell, preventing leakage between the faces. The springs give the

sealing ring enough flexibility to maintain full face contact with the mating ring at constant

pressure during slight shifts in shaft position.

For a rotating mechanical seal in which the leakage is prevented by a Teflon ring, the sealhousing come with a quenching liquid inlet that is required on pumps that operate with a

negative suction pressure. The liquid supplied to the seal prevents air infiltration while

providing lubrication and cooling. If clear fluid is pumped, then the quenching liquid is drawn

directly from the pump discharge, but if the liquid contains foreign particulate matter, aseparator should be installed in the quenching line.


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Figure 3- Rotating Seal

2. Stationary Mechanical Seal

The shell containing the springs and sealing ring is held stationary in the annular space of thepump housing.

The mating ring is fastened rigidly to the shaft, usually against a shoulder, allowing it to rotatewith the shaft.

The sealing ring is forced against the mating ring by the springs, in order to prevent leakagebetween the faces.

O-rings prevent leakage between the sealing ring and shell and between the mating ring andshaft.

Factors such as temperature, pump speed, type of liquid and seal design are among thoseconsidered when choosing materials for sealing and mating rings. Friction between faces should

be kept minimal; hence, materials used are ceramics, stellite, carbon graphite, bronze and

tungsten carbide.

Figure 4- Basic Mechanical Seal with Stationary and Rotating faces


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3. Care of Mechanical Seals

For pumps equipped with mechanical seals, the following precautions should be exercised before and

during operation:

Never run the pump unless it is completely filled with liquid. Before start up, vent all air out of the seal housings. Ensure that an adequate flow of quenching or cooling liquid is flowing to the seals.

Seals should never run in dry condition, since this causes the faces to score and become grooved. An

indication that the seal faces are dry running is by a squealing sound. However, whether or not this

sound is heard does not mean that the problem is not occurring at any point.

Causes of leaking seals:

Seal faces are scored or grooved. Rings are distorted due to disproportionately tightened bolts on the seal housing gland. O-ring or other type gaskets are cut or stolen during installation. Misalignment of piping resulting in distortion of pump parts. Excessive pump shaft vibration. Improper adjustment of the string tension.

bearings

The gears, lobes or impellers in rotating pumps must be kept within closely defined limits. The function

of bearings is to locate the shaft in the running position, which keeps the pumping element in theproper position. Several forces act on the pumping elements, trying to force them out of place:

Radial- forces acting perpendicular to the pump shafts centerline. Axial- forces acting parallel to the pump shafts centerline. Combination of radial and axial.

Causes of radial forces in a pump are:

Gravity acting on the shaft and impeller. Imbalance in the rotating element causes a centrifugal force. Pressure differences on each side of the rotor or impeller develops a force. If the pump is belt or gear-driven, there is a force on the shaft.

Gravity develops the axial force in vertical pumps and the differential pressure between the inlet and

opposite face of an impeller develops axial pressure.


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Many steps may be taken in reducing the amount of axial thrust in single suction and multistage pumps,

however, bearings must be able to maintain the shaft running position when fluctuating because of

operational changes.

There are two types of pump bearings:

Sleeve and shell Ball and roller

Sleeve and Shell Bearings

Small pumps usually have bronze brushings or sleeves fitted around the shaft. The clearance around the

shaft is small, so bearing brackets attached to the casing holds the sleeves in place.

Large pumps have the sleeve bearing, made of two cast iron or steel half shells lined with babbitt

(bearing metal).

This type of bearing is self-aligning so that it can adjust itself to small changes in shaft position

automatically. It is also oil lubricated. Drip lubricators supply the bearings of small pumps with oil.

Endless chains or rings riding on the shaft supply oil to the bearing from the lower part of the bearing

housing, which acts as an oil reservoir, on medium-sized pumps. A shaft-driven oil pump supplies oil

under pressure to the bearings in large pumps.


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Figure 5- Turbine with bearing

Ball and Roller Bearings

These are also called antifriction bearings and have replaced sleeve bearings in a lot of modern pump

designs. Small and medium-sized pump shafts use ball bearings of single row or double row design.

Larger pumps use roller bearings. Antifriction bearings may be lubricated by grease or oil.

Figure 6-Ball Bearings

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