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Pumps & Systems Magazine

PD Pump Fundamentals, Design and Applications (Part One)

Written by Hydraulic Institute PD Pump Members

Pumps & Systems, February 2009

Editor's Note: This is the first in a series of five articles based on the Hydraulic Institute's newPositive Displacement (PD) Pumps: Fundamentals, Design and Applications e-Learning

course. To read the next article in the series, click here.

Positive displacement pumps are used in a myriad of applications across multiple industries.

Users have found them to be the solution to many specific pumping challenges; however, due to

their size, simplicity and ruggedness, they often are not as well understood as other pump types.

Technologies within the extensive positive displacement family enable coverage of a broad

range of horsepower, fluid and pressure applications. These products, therefore, merit increased

consideration in a user's pump selection process. To assist pump users with a proper

understanding of definitions, applications, installation, operation, maintenance and testing

procedures the Hydraulic Institute publishes ten ANSI/HI Standards covering PD pumps

including: Air Operated, Controlled Volume Metering, Reciprocating and Rotary.

Figure 1. Positive Displacement Pump Family Tree.

ANSI/HI standards perform a vital function in pump industry commerce and serve important
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roles in minimizing misunderstandings in the marketplace. The Hydraulic Institute, however, has

extended its mission to include the development of a pump knowledge and education portfolio in

response to member and pump user needs. Among the first key elements are a re-launch of the

Centrifugal Pump e-Learning course and the development of a new Positive Displacement Pump

course covering fundamentals, design and applications. These, and future courses, will be hostedwithin HI's new educational portal, http://www.pumplearning.org/.

Curriculum Overview

The PD pump e-Learning course is a five module internet-delivered learning program designed

to provide users with broad and comprehensive knowledge of positive displacement pumping

technologies. Material is highly visual and interactive, designed to allow students to take full

advantage of the latest internet technology.

Content is arranged in independent modules with each one focusing on markets and applications,

as well as providing basic recommended technical terms and fundamentals for an understandingof positive displacement pump hydraulics. The first two modules in the series are:

Why Positive Displacement Pumps

Positive Displacement Pump Hydraulics

Three other modules are each devoted to a specific positive displacement pump technology. To

enhance the users learning experience, these modules rely heavily on color photographs of

pumps and pumping installations.

Rotary Pumps, including: Vane, Rotary Piston, Flexible Member, Lobe, Gear,

Circumferential, Piston, Progressing Cavity, Timed Screw, Untimed Screw

Reciprocating Pumps, including: Power, Direct Acting, Power Diaphragm, Air

Operated Double Diaphragm, Air Operated Piston

Metering Pumps, including: Torque Sources, Drive Mechanisms, Capacity Control,

Liquid End Reviews
http://www.pumplearning.org/http://www.pumplearning.org/


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Multiple 1500-hp Rotary Pump Heavy Crude Loading Station.

Modules are designed for either self-instruction, instructor lead courses by the twelve PD pump

company sponsors or as HI sponsored webinars. Each module, designed to stand alone or

combined with others, includes an examination and completion certificates suitable for submittal

for PDH or CE credit. [af1]

Pump education courses typically highlight rotodynamic (centrifugal and vertical) pumps, and a

good knowledge of that technology is helpful in understanding positive displacement pumps.Many subjects are common, but certain terms and concepts are unique because PD pumps

involve an entirely different technology.

Centrifugal vs. PD Pumps

In simple terms, a centrifugal pump impeller moves a stream of liquid from the pump suction to

a discharge cone where velocity is gradually decreased and converted to pressure energy. A

positive displacement pump, however, moves a set volume of liquid. Pressure is obtained as

liquid is forced through the pump discharge into the system, thereby converting energy to

pressure.

One example of this principle is demonstrated by reciprocating motion where the movement of a

piston forces liquid out of a closed cylinder, which has (inlet) suction and discharge valves to

control flow. This forms one of the major PD technologies, reciprocating pumps. In portions of

their operating range, reciprocating pumps are the single technology that can successfully

provide the necessary pumping solution.

Rotary pumps constitute the second major positive displacement category in which a pumping

chamber and a pumping element are actuated by the relative rotation of the drive shaft to the

casing. This family is distinguished by having no valves on the inlet or discharge. These types of

pumps are available in a number of different pumping principles, each with its own features and
http://www.pump-zone.com/#_msocom_1%23_msocom_1http://www.pump-zone.com/#_msocom_1%23_msocom_1


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benefits that provide specific pumping solutions.

The third major category is controlled volume metering pump (CVMP). These types of pumps

are often known as chemical injection feed pumps or dosing pumps. Essentially, these are

reciprocating positive displacement pumps configured to accurately dispense a set volume ofliquid in a specified time period. They may include one of several types of mechanisms for

varying the effective displacement. These types of pumps are used in applications requiring

highly accurate, repeatable and adjustable rates of flow.

Pumping Solution Products

Technologies within PD pumps are often called "pumping solution products," as they perform

that function for applications across a broad range of process conditions. For example, rotary PD

pumps can handle highly viscous product (3,000,000 SSU) while reciprocating pumps handle

water thin liquids. PD pumps handle flow rates from less than 1-gpm to 15,000-gpm, and

pressures from a few psi to 70,000-psi and higher. PD pumps, at constant speed, are constantflow rate devices, but centrifugal pumps are variable flow rate devices. Generally, PD pumps

require some type of pressure protection, and certain designs will require pulsation control.

System design requirements are different from centrifugal pumps.

PD pumps may be found almost anywhere, but a generally accepted view is that 90+ percent go

into applications within these top six industrial market segments:

Oil and Gas

Water and Wastewater Treatment

Chemical

Food, Beverage and Pharmaceutical

Power

General Industrial (Marine/Medical/OEM)

Many of these industries represent multiple markets. Oil and gas, for example, has distinctly

different applications for PD pumps across its segments: exploration, production, pipeline,

processing and distribution marketing.

The food and beverage market is another key positive displacement market with multiple

segments such as beverage, bakery, confectionary, dairy and meat packaging.

Selection Consideration: Twelve Benefits of PD Pumps

In many markets, there are applications that clearly should be positive displacement and

applications that are clearly centrifugal. It is important for the user or specifying engineer to

recognize, however, that there are also a broad range of applications where both types should be

considered and selection should be based on the results that the user desires.

In such consideration, there are reasons why positive displacement pumps make an ideal

solution to specific pumping requirements. Twelve suggested reasons to use PD pumps are

summarized below, grouped by fluid characteristics, process conditions, environmental system

requirements and flow control. Additionally, Figure 3 provides a matrix of these 12 reasons


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compared to the primary markets of PD pumps. Some may surprise you.

Figure 3. Matrix Market Application vs. Desired Pump Characteristics

Fluid Characteristics

High Viscosity

Selected rotary technologies and air operated piston pumps easily handle highly viscous fluids.

Due to high friction losses in centrifugal pumps, their flow rate and efficiency start to drop

above 500 SSU. Flow and efficiency in a rotary pump, however, typically increase with

viscosity. PD pumps can handle fluids with viscosities of several million SSU.

Low and Variable Viscosity

PD pumps, such as vane or air operated double diaphragm (AODD), are often applied on very

thin fluids. Other liquids, such as oil, have viscosities that vary with temperature. With variable

viscosity liquids, a moderately small change in viscosity may have a large effect on centrifugal

efficiency but little effect on PD pump efficiency.

Low Shear Pumping Required

In many fluid applications, liquid shear is not a problem; however, it is critical in some

applications. PD pumps excel in the handling of shear sensitive fluids.

Solids Handling Capability

Progressing cavity pumps handling high solids content sludge in a waste treatment plant and

reciprocating pumps are applied on coal slurry pipeline with solids contents as high as 40

percent by weight. This is sometimes a surprising PD pump characteristic, but widely varied

applications serve as examples.

Multi-Phase Flow

A constant source of liquid is a centrifugal pump requirement, but unfortunately all processes do


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not provide such constant sources. If there is insufficient liquid, a gas bubble forms in the

suction and causes loss of prime (the pump stops pumping). PD pumps, on the other hand, are

capable of handling a high percentage of air or gas entrainment.

Process Condition

High Pressure

Beyond the range of centrifugal pumps are many chemical, sandblasting and high-pressure

water-cutting applications where PD pump technology dominates. Figure 4 provides an

overview of the pressure and capabilities among pump technologies.

Figure 4. Technology Flow Pressure Range Chart.

Low Flow

Flow below 100-gpm and above 200-psi provides excellent application opportunities for PD

pump technology.

Efficiency

For viscous fluids where both PD and centrifugal pumps can operate, PD pumps can often be 10

to 40 points more efficient than centrifugal pumps.

Combination of High Pressure/Low Flow-Efficiency Demand

Any of the previous three characteristics individually are a reason to use PD pumps; however, in

applications where all of these conditions occur simultaneously, a PD pump solution is ideal.


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Figure 4 provides an overview of the pressure and capabilities among pump technologies.

Environmental System Requirements

Sealless Pumping (No Shaft Seal)

Magnetic drives and canned motor pumps are available in PD pump designs. The requirement is

also met by designs where the pumping environment does not have a shaft penetration, such as

peristaltic or diaphragm pumps.

Self-Priming and Inlet Conditions

The ability to self-prime is a useful feature for PD pumps as it allows substantial flexibility in

system layout and eliminates the need for suction priming systems. PD pumps are self-priming,

have excellent suction lift capabilities (raising liquids on the suction side) and are capable of

drawing down to near vacuum.

Flow Control

Constant Flow Against Variable System Pressure

At a constant speed, PD pumps deliver practically constant flow. Flow is constant even if the

system pressure varies, which is a desirable condition in certain systems.

Accurate Repeatable Measurement

Since a PD pump is a constant flow device, certain designs that limit slip are ideal for metering

fluids in or out of systems. This application, of course, requires accuracy and repeatability. It

also may need flow variation, which is typically obtained mechanically or electronically by

speed variation.

There is a universe of standard PD solutions in addition to the bakers dozen described here. As

these pumps also must meet many other requirements, manufacturers provide products with

special options such as jacketing, non-corrosive materials and built-in pressure relief valves.

Some PD units have duty cycle limits that users are advised to investigate. It is important to note

PD pumps are constant torque devices. In variable speed applications, VFD drives must be ratedwith that understanding.

Fundamentals of PD Pumps: Online Learning

Extensive material is provided in the HI PD pump e-Learning modules to allow for expanded

and detailed understanding of these items and applications. The course contains more than 500

screens of information in five separate modules for 10 hours of credit work for those seeking

PDH or CE credit.

With the development of Positive Displacement Pumps: Fundamentals, Design and

Applications, HI has again reached a new level in its role of serving member companies and


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pump professionals. The entire five-module course is now available at its website. Recentlydebuted by Hydraulic Institute, PumpLearning.org was created to serve as the ultimate "go to"

center for information on pumps and pumping technologies, and provides knowledge seekers

with a panoply of sources and opportunities to gain state-of-the-art intelligence. Offerings

presented on the new user-focused website include: e-Learning Courses (now featuring HI'slatest course, Positive Displacement Pumps: Fundamentals, Design and Applications, and theupdated and soon-to-be released course, Rotodynamic [Centrifugal] Pumps: Fundamentals,

Design and Applications), webcasts, conferences and special programs jointly sponsored by

renowned industry experts. The site is constantly updated to present users with the latest news,activities and connections to the industry.

Hydraulic Institute is the largest association of pump producers in North America and the"value-add" standard-setting resource for member companies and pump users worldwide.

This course has been created by Positive Displacement Pump experts and HI Sponsors:

ARO/Ingersoll Rand

Colfax-IMO & Warren Pump Flowserve Pump Division

Grundfos Pumps Corporation

Iwaki American Corporation

Leistritz Corporation

Milton Roy Company Moyno, Inc.

Roper Pump

Siemens Water Technologies

Union Pump


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PD Pump Fundamentals, Design and Applications (Part Two)

Written by Hydraulic Institute Positive Displacement Pump Sponsors

Pumps and Sytems, March 2009

Editor's Note: This is the second in a series of five articles based on the Hydraulic Institute'snew Positive Displacement (PD) Pumps:

Positive displacement (PD) pumps are used in a myriad of applications across multiple

industries. Users have found them to be the solution to many specific pumping challenges;

however, due to their size, simplicity and ruggedness, they often are not as well understood as

other pump types.

Technologies within the extensive positive displacement family cover a broad range of

horsepower, fluid and pressure applications. These products merit increased consideration in a

user's pump selection process. To assist pump users with a proper understanding of definitions,

applications, installation, operation, maintenance and testing procedures, the Hydraulic Institute

publishes ten ANSI/HI Standards covering PD pumps including: Air Operated, Controlled

Volume Metering, Reciprocating and Rotary.

ANSI/HI standards perform a vital function in pump industry commerce and serve important

roles in minimizing misunderstandings in the marketplace. The Hydraulic Institute has extendedits mission to include the development of a pump knowledge and education portfolio in response

to member and pump user needs. Among the first key elements are a re-launch of the Centrifugal

Pump e-Learning course and the development of a new Positive Displacement Pump course

covering fundamentals, design and applications.

Last month, we provided an overview of the curriculum and an overview of positive

displacement pumps, as well as the 12 benefits of PD pumps.

This installment will focus on "Positive Displacement Pump Hydraulics," which introduces the

fundamental physical concepts and fluid properties that affect positive displacement pump

selection and operation.

Since many of these properties affect positive displacement pumps differently than centrifugal

pumps, it is critical to understand the interaction between the pump and the fluid, and how the

operation of positive displacement pumps differs from centrifugal pumps. Without this

foundation of fundamental principles, it would be difficult to effectively learn about the myriad

of positive displacement pumps (to be presented in the next three articles).

On the most basic level, pumps are used to provide pressure and/or flow so that the pump user

can accomplish a specified task. With this premise in mind, note that positive displacement

pumps create flow, not pressure. The pressure on the pump is a function of the system's reaction

to the delivered flow due to pipe losses, restrictions and elevation changes. See Figure 1 for an
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explanation of gauge versus absolute pressure; these two different reference points have caused

confusion through the years.

Figure 1. Gauge versus Absolute Pressure

Since positive displacement pumps theoretically generate flow independent of discharge

pressure, Figures 2 and 3 show how the delivered flow rate is affected by the differential

pressure and speed. This is a fundamental difference between positive displacement pumps and

centrifugal pumps. The delivered flow rate is the theoretical flow rate minus the internal slip of

the pump. The slip is the internal leakage that occurs in the pump due to clearances, viscosityand differential pressure, and will vary between pump types and applications.

Figures 2 and 3.


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Of course, nothing comes for free, and every pump requires a certain amount of power to

perform work. The pump input power is comprised of the theoretical liquid horsepower and the

internal power losses at the operating point. The theoretical liquid horsepower is the work done

to move the theoretical volume of fluid from inlet to outlet pressure and is solely based on the

physical dimensions of the pumping elements, the operating speed and the differential pressure.On the other hand, the internal power losses account for the mechanical and viscous losses that

occur as the pump operates. It is typical that the mechanical loss is the major component when

operating at low viscosities, while the viscous loss is larger at high viscosities. These losses in

turn affect the overall efficiency of the pump.

Fluid characteristics play a major role with positive displacement pumps since most of these

pumps are used to handle products other than water. The most important fluid property is

viscosity, which is the fluid's ability to resist a shearing force, or how easily the fluid will flow.

Viscosity affects pump selections due to its impact on operating speed, allowable differential

pressure, suction capability and input power. Since viscosity is typically temperature dependent,

it is important to know what the viscosity values will be over the entire operating temperaturerange, from cold start-up to maximum upset condition. Viscosity can be expressed in many

different units, the most common being SSU, SSF, centipoises (cP) and centistokes (cSt). Units

depend on which viscometer instrument was used to evaluate the different fluids. These values

are tabulated in many texts, and several examples are provided in the module (see sidebar for

more information).

Along with viscosity, it is essential to understand how a fluid reacts to being pumped. A fluid

can have a constant viscosity (at a particular temperature and pressure) regardless of the rate of

shear (known as a Newtonian fluid), or the viscosity can vary with the shear rate and shear stress

(known as a Non-Newtonian fluid). Non-Newtonian fluids are divided into five types: plastic,pseudo-plastic, dilatant, thixotropic and rheopectic. The first three are time independent since the

viscosity is simply a function of the shear stress, while the last two are dependent on both time

and shear stress. To accurately determine the viscosity of non-Newtonian fluids, it is usually

necessary to take measurements at several points. If the apparent viscosity is not accurate, it can

result in an improper pump selection.

Beyond viscosity, several other fluid characteristics relate to positive displacement pump

selection and operation. One of these characteristics is vapor pressure. The vapor pressure is the

absolute pressure at which a liquid changes to a gas (see Figure 4). The primary influence of

vapor pressure is on the Net Positive Inlet Pressure (NPIP) required for the pump. The NPIP is

the absolute pressure above vapor pressure required to get the fluid into the pumping elements.As can be seen with a fixed inlet pressure, the higher the vapor pressure, the less pressure

available to get the fluid into the pump.


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Figure 4. Vapor pressure at 60-deg F in PSI absolute

Net Positive Inlet Pressure plays a key role in pump selection and system design. Since pumps

cannot pull fluid into them, they rely on the difference in pressure between the liquid source and

the pump inlet to get the product into the pump. Sufficient pressure must be available at the

pump inlet to fill the pumping chambers and prevent gas from being released from the fluid.

Therefore, the inlet pressure available must always be greater than the inlet pressure required.

The inlet pressure available is a system characteristic that is determined from the following

factors: atmospheric pressure, elevation of the fluid level (above or below the pump inlet), inlet

line friction losses, vapor pressure, and in the case of reciprocating pumps, acceleration head.Acceleration head, a unique factor for reciprocating pumps, is the pressure required to accelerate

the liquid column at the beginning of each stroke. Depending on the suction line length, average

line velocity, pump rotational speed, number of pistons and liquid elasticity, the acceleration

head can easily be the largest factor of the available inlet pressure calculation.

The inlet pressure required is a pump characteristic that the manufacturer calculates. It is affected

by such factors as pump design, viscosity and speed. Once the available inlet pressure is known,

it can be compared to the inlet pressure required by the pump to determine if the pump will

operate properly. Sometimes several iterations between the user and supplier are required to

select the correct pump.

Once all of the important factors affecting pump selection are understood, hydraulic selection

becomes easier. However, other factors external to the pump need to be evaluated to ensure that

the entire pump system is properly selected. These factors include environmental conditions such

as installation location and electrical requirements, the control philosophy of how the pump will

operate, the utilities available and the operating energy requirements.

All of these factors flow into the life cycle costs of a pumping system, which nearly always

exceed the initial cost of the machine. The life cycle costs, which can be fully explored in the

Hydraulic Institute publication, Pump Life Cycle Costs: A Guide to LCC Analysis for Pumping

Systems, are explained in detail and consist of the initial cost plus such items as installation,


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power, operation, maintenance, downtime and environmental considerations.

This information on PD hydraulics forms the knowledge base for PD pumps (and the HI e-

Learning course), so users can properly evaluate any pumping system and select the best

technological solution based on the entire spectrum of process conditions and system limitations.

In future issues, look for articles devoted to specific positive displacement pump technologies:

Rotary Pumps, including: Vane, Rotary Piston, Flexible Member, Lobe, Gear,

Circumferential, Piston, Progressing Cavity, Timed Screw, Untimed Screw

Reciprocating Pumps, including: Power, Direct Acting, Power Diaphragm, Air Operated

Double Diaphragm, Air Operated Piston

Metering Pumps, including: Torque Sources, Drive Mechanisms, Capacity Control,

Liquid End Reviews


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PD Pump Fundamentals, Design and Applications (Part Three): Rotary Pumps


Pumps and Systems, April 2009

Editor's Note: This is the third in a series of five articles based on the Hydraulic Institute's new

Positive Displacement (PD) Pumps:

Rotary Pump Overview

Rotary pumps are available in a broad range of flow and pressure, which is why they are

recognized by users as the solution for their specific pumping needs. Recent enhancements have

increased the reliability and operating envelopes of rotary pumps. They are increasingly

recognized for their efficiency in today's energy conscious environment.

A rotary pump typically consists of a stationary pumping cavity containing rotating pumpingelements that are actuated by the rotation of the drive shaft. This rotary motion is the

distinguishing feature of this class of pumps-hence the name rotary pump. The pumping

elements are characterized by close fitting running clearances. Rotary pumps have no need for

separate inlet or outlet valves.

Rotary pumps are designed so that the rotating pumping elements draw the fluid at the suction

port into the pumping cavity, transport it through the pumping elements and force it through the

discharge port into the system.

The geometry of the pump elements and pumping cavity determine the volume of fluid pumped

per revolution of the shaft. This volume is called the displacement. Most rotary pump types are

configured for fixed displacement; however, they can produce variable flow rates by varying the

shaft speed. Vane and piston rotary pumps produce variable volume by changing the internal

geometry (i.e., varying the displacement of the pumping elements).

Rotary Pump Types

The most common types of rotary pumps and their subcategories are shown in the rotary pump

tree (Figure 1). This module presents the basic pumping principle for each type of rotary pump,

typical configurations and major components, range of performance and operating capability,

location in the overall rotary pump spectrum, application characteristics, features and benefits

and typical applications and industries served.
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Figure 1

Vane-in-rotor pumps are characterized by moveable vanes, or rigid blades, retained (but not

necessarily fixed) by an eccentric rotor that rotates within the pumping cavity. This action draws

fluid in and forces fluid out of the pumping chamber, thereby delivering flow. Vane pumps canbe either fixed or variable displacement.

In rotary piston pumps, fluid is drawn in and forced out by multiple pistons that reciprocate

within cylinders in the cylinder block, producing flow. There are two basic types: axial and

radial piston. Both types are available as fixed and variable displacement pumps.

Flexible member pumps transfer the product from the inlet to outlet by making use of the

elasticity of the flexible member(s). The flexible members may be a tube, vanes or a liner.

Lobe pumps carry the pumped fluid between rotor lobe surfaces and the pumping chamber from

the inlet to the outlet. In this regard, they are similar to gear pumps but do not produce the sheareffects. Timing gears are used to coordinate the motion of the lobe surfaces, avoid surface

contact and provide continuous sealing.

Gear pumps carry the pumped fluid between gear teeth and displace it when the gears mesh. The

surfaces of the gears cooperate to provide continuous sealing, trap pockets of the pumped fluid

and push it out the discharge port. One of the gears drives the other idler or driven gears. There

are two main variations-external and internal gear pumps.

Circumferential piston pump rotors are timed and each rotor has one or more wing lobe

elements, called pistons. There is no sealing contact between the piston surfaces.

Single-screw pumps (commonly called progressing cavity pumps) have a rotor with external

threads and a stator with internal threads. The geometry of the rotor and stator form cavities that

progress from inlet to outlet as the rotor rotates, which creates the pumping action.

Multiple screw pumps are divided into two broad families-timed and untimed. Typically,

multiple screw pumps have two or more intermeshing screws and the flow is in the axial

direction. The inlet fluid, which surrounds the rotors, is trapped as the screws rotate. With the

rotors in tight fitting bores and the casing acting as a stator, the fluid is moved uniformly with

the rotation of the rotors along the axis and forced out at the other end.


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Application Analysis

The application analysis stage is a vital step in the pumping solution process. Rotary pumpapplication benefits from careful attention to the performance requirements of the system. This

process determines initial affordability, flexibility to cover the entire operating range of the

application, reliability and energy efficiency. It is important that the purchaser/user understand,

identify and communicate the requirements to the pump supplier.

A recommended sequence is to first consider the characteristics of the fluid(s) to be pumped (A),

then the operating conditions the process requires (B), and finally the resultant hydraulic

requirements of the system (C) (see Figure 2).

Figure 2

Self priming is an important advantage rotary pumps have over rotodynamic pumps. There isconsiderable variation in suction capability among rotary pump types due to the design of the

pumping elements and the inlet configuration. It is important to remember that the fluid to be

pumped is pushed into a pump by the pressure differential available at the pump inlet. Therefore,

special attention should always be focused on inlet conditions. Users and system designers are

always well advised to make sure the Net Positive Inlet Pressure Available (NPIPA) from the

system exceeds Net Positive Inlet Pressure Required (NPIPR) by the pump and includes a

reasonable margin.

Because a rotary pump will deliver an essentially constant volume of fluid per shaft revolution

regardless of system pressure, it is necessary when applying rotary pumps to provide protection

against over-pressurization in the event of a system malfunction.

Pump Selection

Delivered flow from a rotary pump is dependent on its displacement per revolution, speed of

operation and slip flow. Even though rotary pumps are characterized by close internal

clearances, there will be some leakage between high pressure outlet and low pressure inlet areas

within the pump. This leakage is called slip and may be large or small depending on the type of

rotary pump, the fluid characteristics and the operating conditions.

Rotary pump input (brake) horsepower requirements vary as a function of the pump type and

operating conditions in each application. Input power is the sum of the power required to move


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the theoretical flow volume of the pump against differential pressure plus internal power losses.

Internal power losses occur because it is necessary to overcome mechanical friction from the

moving parts of the pump and the viscous drag effects and shearing of the pumped fluid.

With many types of rotary pumps available, selection of the proper pump for the applicationmay seem complex. The pump selection process involves matching the properties of the pumped

fluid, operating conditions, and system requirements identified in the Application Analysis with

a pump's capabilities. The performance capability of the rotary pump selected must be verified

over the full range of required operating conditions.

The Rotary Pump Module provides two useful tools to help narrow the choice of rotary pump

types (reproduced in Figures 3 and 4):

A Consolidated Range Chart where the flow and pressure envelope of each rotary pump type is

depicted (see Figure 3). With knowledge of the full range of flow and pressure requirements of

the application, suitable rotary pump types can be identified on the range chart. Consultation

with the supplier is recommended to confirm specific application recommendations and to

investigate special designs, which are often available to provide unique solutions.

A Capability Table provides an overview of operating ranges and application characteristics for

the rotary pump types covered in the course (see Figure 4). Some relative capabilities such as

abrasive handling, shear sensitivity and pulsation, which are highly dependent on applicationconditions and the pump technology to which the comparison is made, are also shown in the

table. Shear sensitivity relates to the effect the pump has on the pumped fluid. The abrasive

handling capability ratings allow inclusion of material enhancements. By matching requirements

to capabilities, applicable rotary pump types can be identified.


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Figure 4

Energy Efficiency and Power Savings Benefits of Rotary Pumps

Energy assessments require examination of the full range of pump system application

parameters, so specific study is recommended.

Rotary pumps are known for the ability to pump viscous fluids more efficiently. Figure 5 uses

HI/Europump Life Cycle Cost Guideline data and compares maximum attainable rotary

efficiencies to maximum attainable rotodynamic efficiencies. Specific attractiveness can be

identified for applications with viscosities as low as 10 cSt (60 SSU) and differential pressures

above 50-psi. It should also be noted that the chart is based on operating a centrifugal pump at

its best efficiency point (BEP). If the pump is installed in a system where pressures vary, the

centrifugal pump will typically move on its operating curve to a lower efficiency region.

Figure 5

Having a working knowledge of rotary pump fundamentals and the specific process application

and/or system for which the pump is being selected is essential for a good pumping solution.

Basic differences in operating capability can be used to guide rotary pump type selection.

Selecting the right pump to match the system and its operational requirements is key to reliable

operation and low ownership cost.


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PD Pump Fundamentals, Design and Applications (Part Four): Reciprocating

Pumps

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Pumps and Systems, May 2009

Editor's Note: This is the fourth in a series of five articles based on the Hydraulic Institute's new Positive

Displacement (PD) Pumps:

Reciprocating Pump Overview

Since the third century B.C. when an Alexandrian named Ctesibus built a basic hand pump that could transfer

water, reciprocating pumps have played a significant role in the development of the modern world. Today,

reciprocating pumps have developed into technically advanced machines capable of delivering more than

40,000psi of fluid pressure.

Reciprocating pumps comprise a major segment of the positive displacement technology category.

Reciprocating pump designs can pump a full range of liquid types including low viscosity chemicals, high

particle content slurries and high viscosity materials. Given this wide operating range, they are often the

technology of choice for difficult applications.

One main difference between rotodynamic and reciprocating pumps is that for a given speed, the rate of flow

of a rotodynamic pump can be varied from zero flow to a maximum flow. Conversely, reciprocating pumps

will have a constant flow for a given speed. Pumps that belong to the reciprocating pump family have several

common operating characteristics, including a constant fluid delivery per stroke and mechanical trapping of

fluid using suction and discharge valves.

Inherent to their reciprocating motion, these pumps also typically produce pulsation. Consideration for

additional devices to reduce pulsation, such as pulsation dampeners or attenuators, may be needed for some

applications. Additionally, as with many PD pump types, systems may require overpressure relief protection.

Efficiencies of reciprocating pumps vary widely across the category due to driver types and mechanical

configurations.

Types of Reciprocating Pumps

Four common types of reciprocating pumps-power pumps, power diaphragm pumps, air operated diaphragm

pumps and air operated piston pumps-are reviewed in the reciprocating pump module.

Power pumps are reciprocating machines where plungers or pistons are driven within a valved cylinder by a

power end. The power end (see Figure 1) converts the rotary motion of a motor-electric, air or hydraulic or

diesel engine-into reciprocating motion by means of a crankshaft, connecting rods and crossheads. The liquid

end (see Figure 2) connects to the power end and contains the plungers, packing, fluid chambers and valves.

The reciprocating motion of the plunger in concert with the other liquid end components can develop more

than 40,000psi of fluid pressure or more than 4,000gpm of fluid flow. These pumps typically have one, two,

three, five, seven or nine connecting rods and crossheads that drive an equal amount of fluid plungers.

Configurations of an odd amount of cylinders are preferred to reduce pulsation. Pulsation is generated by the

oscillating pressure of each fluid chamber from suction pressure to discharge pressure. The oscillating

pressure, cycling at 50- to 500-rpm, is a popular driver of pump failures, but these pumps are constructed

robustly to resist fatigue.

It is important to control pressure with power pump systems. As the pump injects the displaced liquid into the

discharge system, the pressure is increased. The pressure will continue to increase until it meets the


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requirement of the system. However, if the system pressure requirement is not controlled, the pressure will

continue to build up until something ruptures in the system or the pump or the driver of the pump stalls out.

Power pumps should be equipped with a pressure relieve device to prevent the over-pressurization of the

system beyond its recommended limits.

Power pumps are typically used for low viscosity chemicals, oils, high pressure cleaning, ore slurries, drilling

mud, reverse osmosis, saltwater injection, hot oil applications, blow out preventers and subsea applications.

Figure 1. Power End for a Power Pump


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Figure 2. Liquid End for a Power Pump

Air operated diaphragm pumps combine the reciprocating motion of a flexible membrane, called a diaphragm,with check valve mechanisms to transfer fluid. These pumps typically have two diaphragms connected to a

reciprocating shaft in which one side of the diaphragm is in contact with the liquid being pumped and the

other side is in contact with the compressed air. The reciprocating motion is created by an air motor that

alternates pressurization of the two diaphragms. Fluid pressure is usually equivalent to the supply air pressure

of the pump; however, amplification devices allow specialized pumps to operate at pressures up to three times

the supply pressure.

Diaphragm pumps are available in many materials of construction, have no rotating seals, are physically

compact and require no electricity connected to the pump for operation (see Figure 3). These characteristics

make air operated diaphragm pumps ideal for the transfer of corrosive and abrasive fluids and operation in

volatile environments, installations where space is limited and portability is required. Other benefits of thesepumps are the ability to self prime, run dry and pass solid entrained fluids.


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Figure 3. Diaphragm pump

Air operated piston pumps use a reciprocating piston and check mechanisms to produce fluid flow and

pressure. As they have the ability to produce fluid pressures in excess of 6,500-psi, these pumps are popular

for pumping viscous fluids such as sealants, adhesives, inks and lubricants. Piston pumps typically meet the

needs of unique applications that require equipment designed for a particular dispensing, metering or fluidtransfer job. As a result, piston pumps are built in many styles and configurations to serve specific needs of

users.

The air motor and lower end (see Figure 4) are the two major components that control the flow rate and

pressure of the pump. The air motor converts compressed air into a reciprocating motion and is available in

several sizes that are defined by the diameter of the air piston. The air motor consists of a major piston

connected to the lower end. Driven by the air motor, the lower end uses the reciprocating motion of a smaller


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diameter piston to create fluid pressure and flow. The ratio of the larger area of the air motor piston to the

smaller lower end piston allows for the amplification the fluid pressure over that of the supply air pressure.

For example, if the pump is being operated by 100-psi supply air and the air motor piston is four times the

area of the lower end, then the fluid pressure would be 400-psi.

Figure 4. Air operated piston pump

Power diaphragm pumps are designed to combine important advantages of reciprocating plunger and

diaphragm pumps. This is done by providing two separate liquid paths, one for the fluid being pumped and

one for hydraulic fluid that pressurizes the pumping fluid (see Figure 5). This eliminates the dynamic seal in

the pumped fluid loop required with reciprocating plunger pumps and enables leak free operation.


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Figure 5. Hydraulic power circuit on right (blue) and pumped fluid circuit (left)

A diaphragm separates these two fluid circuits; suction and discharge valves control the flow in the pump

fluid circuit. The diaphragm is the pumping element and its reciprocating motion is induced by the plunger

displacing hydraulic fluid. Pumped liquid leakage can occur if a diaphragm is ruptured, but this is prevented

by the use of multilayered diaphragms with integral alarm functions. These features allow the fluid to be

contained in the pump even when one diaphragm is damaged.

Power diaphragm pump designs are modular, allowing for electric motor driven power frames with multiple

pumping heads. Configurations can be simplex, duplex, triplex (see Figure 6), quadrauplex or septuplex. Inmulti-head configurations, common suction and discharge manifolds provide a reduction in pulsation due to

partially overlapping flows. Standard pump configurations are available from manufacturers; however, highly

customized units are common with special valves, heating/cooling jackets and wetted parts materials such as

titanium, duplex steel or Hastelloy.


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Figure 6. A triplex power pump configuration

Power diaphragm pumps provide efficient leak free pumping to 1,200-bar (18,000-psi) on a broad range of

fluids including fluids that are environmentally damaging, valuable, abrasive or viscous (up to 250-kcSt).

These pumps have proven their safety and reliability in numerous applications including chemical process,

nuclear, pharmaceutical, cosmetics, biological processes, foodstuffs, and onshore and offshore petrochemical

installations.

Pump Selection and Application Analysis

Pump selection is a complex and highly technical process that should be completed by a trained professional.

The reciprocating pump-training module addresses the individual considerations required for selection of each

type of reciprocating pump. There are some common guidelines for specifying a reciprocating pump for an

application. Three common categories requiring consideration are fluid properties, environmental conditions

and system requirements.

The fluid being pumped is evaluated for viscosity, specific gravity, temperature, solids content and its

compatibility with the pump's materials of construction. All components that come in contact with the fluid

must resist corrosion including pump casing materials, seals, packing, diaphragms, plungers and valves. The

specified materials of construction for the pump are often the main drivers of its cost. Highly corrosive fluids


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may require more expensive materials like stainless steel, Alloy C, PVDF, PTFE and Viton; more inert

fluids can be compatible with less expensive materials like aluminum, steel, synthetic rubber and thermo

plastic elastomers.

Similar to fluid properties, environmental conditions can affect the pump's construction. Atmosphericconditions may require special material pump materials to resist corrosion or ensure groundability in volatile

environments.

System parameters such as piping configuration, inlet elevation, outlet elevation, power availability, operating

pressure and flow rate are used to determine the best reciprocating pump type and size for the application.

These system characteristics in combination with the fluid properties allow for validation that the

reciprocating pump will be able to prime and deliver the specified amount of flow and pressure. Specification

criteria such as net positive suction head available (NPSHA) from the system, net positive suction pressure

required (NPSHR) by the pump and discharge head required by the system are influenced by the above

parameters.

When the demands required by the system are calculated and understood, then the pump types that best fit the

application can be selected using a range chart (see Figure 7). It is often the case that more than one type of

reciprocating pump is suitable for an application; it is then up to the preference of the user to assess the

unique features and benefits that each technology has for the application.


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Figure 7. Range chart for the reciprocating pumps


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With the development of Positive Displacement Pumps: Fundamentals, Design

and Applications, HI has again reached a new level in its role of serving

member companies and pump professionals. Recently debuted by HydraulicInstitute, PumpLearning.org was created to serve as the ultimate "go to" center

for information on pumps and pumping technologies, and provides knowledgeseekers with a panoply of sources and opportunities to gain state-of-the-art

intelligence.

Offerings presented on the new user-focused website include: e-LearningCourses (now featuring HI's latest course, Positive Displacement Pumps:

Fundamentals, Design and Applications, and the updated course, Rotodynamic[Centrifugal] Pumps: Fundamentals, Design and Applications), webcasts,

conferences and special programs jointly sponsored by renowned industry

experts. The site is constantly updated to present users with the latest news,activities and connections to the industry.

Hydraulic Institute is the largest association of pump producers in North

America and the "value-add," standard-setting resource for membercompanies and pump users worldwide.

This course has been created by Positive Displacement Pump experts and HISponsors:

Ingersoll Rand ARO Fluid Products

Colfax-IMO & Warren PumpFlowserve Pump Division

Grundfos Pumps CorporationIwaki America IncorporatedLeistritz Corporation

LEWA Inc.Milton Roy Americas

Moyno, Inc.

Roper Pump CompanySiemens Water Technologies

CLYDEUNION

PD Pump Fundamentals, Design and Applications (Part Five): Metering Pumps

http://www.pump-zone.com/pumps/reciprocating-pumps/pd-pump-fundamentals-design-and-applications-part-five-metering-pumps.htmlhttp://www.pump-zone.com/pumps/reciprocating-pumps/pd-pump-fundamentals-design-and-applications-part-five-metering-pumps.html


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Pumps and Systems, June 2009

Editor's Note: This is the fifth in a series of five articles based on the Hydraulic Institute's new

Positive Displacement (PD) Pumps

Metering Pump Market Overview

When Robert Sheen invented the metering pump in the 1930s, the core of his invention was a

method of controlled volume that was inherent to the pump. The metering pump did not depend

on a bypass valve after the discharge; speed changes to the pump by replacing belts, pulleys or

motors; changes to the pump size to limit the amount of chemical dosed to a specific application

of boiler feed or cooling tower chemicals; or the operator diluting the chemicals to match the

pump's application rate. The means of controlled volume easily limited the pump's actual output

while providing dependable accuracy and reducing performance monitoring and labor time in

the chemical feed industry.

Since the original controlled volume pump, the terms metering pump, controlled volumemetering pump and dosing pump have emerged as popular synonyms for this category. During

the past 75 years, there have also probably been more inventions related to metering pumps than

any other pump type. These inventions have typically related to producing a controlled

limitation of flow rather than improving flow inducement. Electronics and robotics have most

recently advanced controlled volume metering pumps. The level of the pump's self-contained

flow management and automatic capacity correction will be further advanced in the decade

ahead.

All of this innovation in the metering pump market is due to the many industries with needs for

repeatedly sustainable accuracy in chemical dosing. In the various applications for metering

pumps, process pressures can range from atmospheric pressure up to 50,000 psig (3500 Bar).

Pump capacities per head vary from 10 milliliters per hour up to 5,000 gallons per hour. To meet

this wide range of requirements, several types of metering pumps have evolved for each

application. Figure 1 summarizes the various drives, control methods and liquid end

combinations designed to handle the full scope of applications.

Figure 1

Accuracy on three levels has become the primary benefit of this type of pump in the delivery of

additives to automated processes, as well as those with the simple mission of maintaining

accurate constant flow. Different versions and forms of metering pumps have sustainable,

accurate capacity control inherent to the pumps themselves, which is distinguishable from

pumps installed with speed control motors and pumps in systems with control valves to divert or


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limit flow to the injection point.

Figure 2

Metering Pump Drive Systems

Controlled volume pumps have never been greatly impacted by changes in system conditions,

and the newest technologies in metering pumps automatically adjust to keep the output accurate

to the set point, even when discharge pressure changes. At the same time, recent innovations

have made it easier for the operator to set metering pumps to the desired discharge rate with

minimum or no need to calculate between capacity change due to stroke length setting versus

capacity.

Many controlled volume pumps today incorporate both stroke length and stroke frequency/speed

in order to provide the user with up to 100 to 1 capacity variation. Today's electronics enablewider speed variation and extreme accuracy, eliminate the need to vary the stroke length and

avoid the hydraulic difficulties inherent to running pumps at less than full stroke length.

The first controlled volume metering pumps incorporated an electric motor with a belt and

pulley drive. The drive types commonly used today include standard AC motors. Solenoid drive

systems are probably the most popular today due to competitive pricing. AC and DC variable

speed motors are used in conjunction with stroke length control in some types. Pneumatic and

hydraulic power sources are found in specialty applications like natural gas and agriculture.

Advanced electric motors, taken from the robotic and computer industry (i.e., stepper motors),

have recently eliminated the need for stroke length control, simplifying setup and operation.


32/34

In the original metering pump, capacity was changed by adjusting the stroke length of the piston,

which was located on the outside of the pump. Figure 3 is essentially the same concept, but

represents a technology introduced about 30 years after the first metering pump. In this concept,

the stroke length adjustment function was moved to an internal, oil bathed gear system. This

drive type is readily available today.

Figure 3

The choice of drive system is important to the application as it relates to durability, accuracy,automation levels, maintenance availability and cost. From the simplest timed triggering of a

solenoid to electric motor driven drives as depicted above, all incorporate some capacity change.

While speed was initially a secondary control method introduced to extend the turndown ratios

from the 2 to 1 or 3 to 1 limits and up to 10 to 1, speed was immediately seen as a preferred

capacity control in some applications. Speed brought problems for relative accuracy.

The Value of a Metering Pump

Within the applications best served by dosing or metering pumps, economics should be

considered to select the best value for a particular application. Unlike most other pumps, cost of

ownership or life cycle cost of dosing pumps is usually not heavily influenced by powerconsumption and repair costs. A more likely case can often be made for savings in the cost of

chemicals metered due to high level accuracy or the quality of a final product.

Users choosing metering pumps are often attracted to the simple convenience of a pump with a

compact package and a built-in capacity adjustment. Factors such as steady state accuracy (see

Figure 2), repeatability and linearity represent even greater value in the majority of applications

where dosing pumps are found today. Today's controlled volume pump accuracy can dispense

the desired amount of liquid during extended periods of time, even as the process requires the

pump's discharge rate to be changed. The capacity ranges as much as 1,000 to 1 in some styles

of these pumps.


33/34

While convenience of flow rate adjustment can cause an engineer to initially consider variable

capacity pump systems, the value diminishes quickly if the operator cannot depend on the pump

repeatedly metering the same or planned variance of chemicals at the predetermined settings

necessary to the process. The costs of compensating for variable capacity pumping systems thathave low accuracy rates can be extremely high in the form of extra components in the system or

poor quality results in the process (see Figure 4).

Figure 4

Conclusion

Matching the right liquid end to the right drive mechanism is how this class of pumps provides

operators with precise delivery of liquids. The metering pump has evolved from the original

packed plunger heads to diaphragm liquid ends that incorporate sensors as a means of

monitoring operation and accuracy.

With the development ofPositive Displacement Pumps: Fundamentals, Design andApplications, HI has again reached a new level in its role of serving member companies andpump professionals. The entire five-module course is now available at

www.PumpLearning.org. Recently debuted by Hydraulic Institute, PumpLearning.org was

created to serve as the ultimate "go to" center for information on pumps and pumping

technologies, and provides knowledge seekers with a panoply of sources and opportunities to

gain state-of-the-art intelligence.
http://www.pumplearning.org/http://www.pumplearning.org/http://www.pumplearning.org/


34/34

Offerings presented on the new user-focused website include: e-Learning Courses (now

featuring HI's latest course, Positive Displacement Pumps: Fundamentals, Design and

Applications, and the updated course, Rotodynamic [Centrifugal] Pumps: Fundamentals,

Design and Applications), webcasts, conferences and special programs jointly sponsored by

renowned industry experts. The site is constantly updated to present users with the latest news,activities and connections to the industry.

Hydraulic Institute is the largest association of pump producers in North America and the

"value-add," standard-setting resource for member companies and pump users worldwide. For

more information, go to www.Pumps.org .

This course has been created by Positive Displacement Pump experts and HI Sponsors:

Ingersoll Rand ARO Fluid Products

Colfax-IMO & Warren Pump

Flowserve Pump Division

Grundfos Pumps Corporation

Iwaki America Incorporated

Leistritz Corporation

LEWA Inc.

Milton Roy Americas

Moyno, Inc.

Roper Pump Company

Siemens Water Technologies

CLYDEUNION
http://www.pumps.org/http://www.pumps.org/

pd pump overview [hi]

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