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Positive Displacement Pumps
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AlChE Equipment Testing Procedure
Positive Displacement Pumps
A Guide to Performance Evaluation
Prepared by the
Equipment Testing Procedures Committee
AlChE
New York
B I C E N T E N N I A L
B I C E N T E N N I A L
WILEY-INTERSCIENCE
A John Wiley & Sons, Inc., Publication
A I /""* UKiiC
z\ir
It is sincerely hoped that the information presented in this document will lead to an even more impressive performance by the chemical processing and
related industries. However, the American Institute of Chemical Engineers, its employees and consultants, its officers and directors, Equipment Testing
Procedures Committee members, their employers, and their employers' officers and directors disclaim making or giving any warranties or
representations, express or implied, including with respect to fitness, intended purpose, use or merchantability and/or correctness or accuracy of the
content of the information presented in this document. Company affiliations are shown for information only and do not imply approval of the
procedure by the companies listed. As between (1) the American Institute of Chemical Engineers, its employees and consultants, its officers and
directors, Equipment Testing Procedures Committee members, their employers, and their employers' officers and directors, and (2) the user of this
document, the user accepts any legal liability or responsibility whatsoever for the consequences of its use or misuse.
A joint publication of the Center for Chemical Process Safety of the American Institute of Chemical Engineers and John Wiley & Sons, Inc.
Copyright © 2007 by the American Institute of Chemical Engineers. All rights reserved.
Published by John Wiley & Sons, Inc., Hoboken, New Jersey.
Published simultaneously in Canada.
No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical,
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222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 750-4470, or on the web at www.copyright.com. Requests to the Publisher for
permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax
(201) 748-6008, or online at http://www.wiley.com/go/permission.
Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no
representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties
of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The
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information about Wiley products, visit our web site at www.wiley.com.
Wiley Bicentennial Logo: Richard J. Pacifico
Library of Congress Cataloging-in-Publication Data is available.
ISBN 978-0-470-18097-6
Printed in the United States of America.
10 9 8 7 6 5 4 3 2 1
Positive Displacement Pumps
AMERICAN INSTITUTE OF CHEMICAL ENGINEERS
EQUIPMENT TESTING PROCEDURES COMMITTEE
Chair: Richard P. O'Connor
R.P. O'Connor and Associates, LLC
POSITIVE DISPLACEMENT PUMPS
PROCEDURE SUBCOMMITTEE
Chair: L. Nelik, Ph.D., PE, APICS
Pumping Machinery Company
Go-Chair: Luis F. Rizo, PE
GE Plastics
General Committee Liaison: Prashant Agrawal, PE
Kellogg Brown and Root
S. Dennis Fegan, Hermetic Pumps, Inc. & Robert J. Hart, E.I. du Pont (Retired)
Working Committee
Bearings and Rotor Dynamics Section Diaphragm Pumps Section
Dr. G. Kirk
G. Lent
University of Virginia
Wilden Pumps
Piping Section
L.F. Rizo, PE
GE Plastics
Progressing Cavity Section
A. Wild
Moyno Industrial Products
Reciprocating Pumps Section
L. Warren
Cat Pumps
Reliability Section
J. Joseph
Amoco
Rotary Section
J. Brennan
IMO Pump
Rotary Section
J. Purcell
Roper Pump
Seals Section
J. Netzel
John Crane
Approved for publication by AlChE's Chemical Engineering Technology
Operating Council on February 16, 2007.
AlChE Equipment Testing Procedure
Equipment Testing Procedures Committee
Chair: Richard P. O'Connor, P.E.
R.P. O'Connor and Associates, LLC
Vice Chair: James D. Fisher, P.E.
Amgen, Inc.
Past Chair: P. C. Gopalratnam, Ph.D., P.E.
INVISTA S.a.r.l.
CTOC Liaison: Gavin Towler
UOP
AlChE Staff Liaison: Stephen Smith
General Committee Members
Prashant D. Agrawal, P£
KBR
Robert E. McHarg, P£
UOP (Retired)
S. Dennis Fegan
Hermetic Pumps, Inc.
Anthony L. Pezone, PE
Consultant
J.F. Hasbronck, PE
Hasbrouck Engineering
Rebecca Starkweather, PE
Scientex LC
Dr. John G. Knnesh, PE
FRI (Deceased)
Thomas H. Yohe, PE
Yohe Consulting
VI
Positive Displacement Pumps
Table of Contents
100.0 INTRODUCTION
1
200.0 EXTENDED DEFINITIONS OF MAJOR TERMS, WITH EXPLANATIONS,
CONVERSION FACTORS, AND NOMENCLATURE
3
200.1 Positive Displacement Pump
3
200.2 Fluid versus Liquid
3
200.3 Flow
3
200.4 Pressure
3
200.5 Net Positive Inlet Pressure (NPIP)
3
200.6 Power
4
200.7 Efficiency
4
200.8 Torque
5
200.9 Viscosity
5
200.10 Specific Gravity
5
200.11 Revolutions per Minute (rpms)
5
200.12 Extended Definitions
5
300.0 TYPES OF PUMPS COVERED IN THIS PROCEDURE
7
300.1 Gear Pumps
8
300.2 Lobe Pumps
9
300.3 Multiple Screw Pumps
9
300.4 Vane Pumps
10
300.5 Progressive Cavity Pumps
11
300.6 Diaphragm Pumps
11
300.7 Piston/Plunger Pumps
12
400.0 GENERAL NOTES ON TEST PREPARATION L O G I S T I C S INSTRUMENTS AND METHODS OF MEASUREMENT
400.1 Flow
400.2 Pressure
400.3 Power and Efficiency
400.4 Temperature
13
13
13
13
15
500.0 TESTING ROTARY PUMPS (GEAR, MULTIPLE SCREW, LOBE, AND . . . . 16
VANE PUMPS)
501.0 Test Equipment
17
501.1 Shaft Speed
17
501.2 Suction and Discharge Pressures
17
501.3 Fluid Viscosity at Range of Temperatures
17
501.4 Flow Rate
18
501.5 Input Power
18
502.0 Standardized Tests
18
502.1 Performance Test
18
502.2 Minimum Required Suction Pressure Test
20
vii
AlChE Equipment Testing Procedure
503.0 Other Tests
503.1 Sound Pressure Level
503.2 Vibrations and Temperature
504.0 Test Process Example
504.1 Performance Test
504.2 Observations
504.3 Minimum Required Suction Pressure Test
504.4 Observations
504.5 Other Tests
22
23
23
23
24
27
29
30
30
600.0 PROGRESSIVE CAVITY PUMP TESTING
601.0 Test Equipment
601.1 Shaft Speed
601.2 Pressure Instrumentation
601.3 Fluid Viscosity
601.4 Flow Measurement
601.5 Input Power
602.0 Tests
602.1 Performance Tests
602.2 NPSH Test
603.0 Other Tests
603.1 Sound Pressure Level
603.2 Vibration Measurements
603.3 Temperature Measurements
603.4 Miscellaneous
31
31
31
32
32
32
33
33
34
34
34
34
34
35
35
700.0 AIR-OPERATED DIAPHRAGM PUMPS
700.1 Recommended Installation
700.2 Access
700.3 Air Supply
700.4 Elevation
700.5 Flexible Connections
701.0 Test Equipment
701.1 Inlet Air Pressure
701.2 Fluid Discharge Pressure
701.3 Fluid Inlet Pressure
701.4 Process Fluid Temperature
701.5 Environment and Inlet Air Temperature
701.6 Viscosity
701.7 Specific Gravity
701.8 Ambient and Inlet Air Relative Humidity
701.9 Air Consumption
701.10 Flow
36
36
36
36
36
36
37
37
37
38
38
38
38
39
39
39
39
vm
Positive Displacement Pumps
701.11 Sound
701.12 Blow-by
702.0 Tests
702.1 Performance Test
702.2 Life Test
703.0 Other Tests
703.1 Blow-by
703.2 Dry Vacuum
703.3 Wet Vacuum
703.4 Sound Test
704.0 Field Test Process Example
704.1 Performance Test
704.2 Observation
40
41
41
41
44
44
44
44
45
46
46
47
47
800.0 RECIPROCATING POSriWE DISPLACEMENT
PUMP (RPDP) TESTING
800.1 Safety Precautions
800.2 Piping
800.3 Test Objective
801.0 Test Equipment
801.1 Shaft Speed
801.2 Suction Pressure
801.3 Discharge Pressure
801.4 Differential Pressure
801.5 Crankcase Temperature
801.6 Liquid Temperature
801.7 Vapor Pressure
801.8 Viscosity
801.9 Flow Rate
801.10 Input Power
802.0 Standardized Tests
802.1 Performance Test
802.2 Inlet Pressure Trace
803.0 Other Tests
803.1 Sound Pressure Level
803.2 Analysis of Results
804.0 Test Process Example
51
51
51
52
53
53
53
54
54
54
55
55
55
55
56
56
56
57
57
57
57
57
900.0 AUXILIARIES
900.1 Appendix A: Seals
900.2 Appendix B: Bearings and Rotor Dynamics
900.3 Appendix C: Piping
900.4 Appendix D: Installation
61
61
63
64
65
1000.0 REFERENCES AND BIBUOGRAPHY
73
IX
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AlChE Equipment Testing Procedure
List of Figures
Figure 1. Types of positive displacement pumps
7
Figure 2: Types of kinetic (centrifugal) pumps
8
Figure 3: External gear pump
9
Figure 4: Internal gear pump
9
Figure 5: Lobe pump internals
9
Figure 6: Two-screw pump
9
Figure 7: Three-screw pump
9
Figure 8: Vane pump
10
Figure 9: Progressive Cavity pump
11
Figure 10: Diaphragm pump in operation
11
Figure 11: Piston pump cross-section
12
Figure 12: Installation and set-up for pump performance field test
19
Figure 13: Example of pump performance curves
20
Figure 14: Minimum suction pressure test set-up
21
Figure 15: Minimum suction pressure results
22
Figure 16: Sample installation for a rotary pump test
25
Figure 17: Performance curve drawn from data in Table 6
27
Figure 18: Performance comparison to the manufacturer's catalog curve
28
Figure 19: Minimum required suction pressure test graph
30
Figure 20: Typical installation of a test pump
37
Figure 21: Typical installation of a pump test system
47
Figure 22: Sample flow curve
50
Figure 23: Horizontal triplex pump
58
xi
Positive Displacement Pumps
Figure 24: Typical anchors for the pump piping
65
Figure 25: Rough alignment phase
66
Figure 26: Baseplate leveling pads and grout location
67
Figure 27: Typical anchor bolt and leveling wedges
67
Figure 28: Potential bolt-bound situation due to tight clearances between bolt,
feet, and base
68
Figure 29: Rough alignment after grouting
69
Figure 30: Final connection of the suction piping
69
Figure 31: Final piping
70
Figure 32: Overhead view of the motor and pump
71
Figure 33: Piping alignment verification
72
List of Tables
Table 1: Basic conversion factors
6
Table 2: Typical power factor correction table
14
Table 3: Performance test report form
16
Table 4: Time trending of basic parameters
24
Table 5: Raw performance data for rotary pump test
26
Table 6: Calculated parameters for performance test
26
Table 7: Minimum required suction pressure test (field data)
29
Table 8: Datasheet for field test of air-operated diaphragm pump
40
Table 9: Flow test datasheet showing start-up pressure
42
Table 10: Test inspection log for life test
43
Table 11: Vacuum test datasheet
45
Table 12: Sound test datasheet
46
xii
AlChE Equipment Testing Procedure
Table 13: Example of a field test datasheet for an air-operated
diaphragm pump in a water transfer application
48
Table 14: Data from a sample flow test
49
Table 15: Data collection table for reciprocating pump test
52
Table 16: Test results
58
Table 17: Calibration table
59
Table 18: Inlet pressure trace
60
Table 19: Materials data for pump internals
63
Xlll
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Positive Displacement Pumps
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Positive Displacement Pumps
100.0 INTRODUCTION
The main objective in creating this document is to provide pump users with a concise,
easy to read, illustrated field-testing procedure. The goal was to take into account the
"imperfect" realities of actual field conditions, with all the obvious restrictions and
emphasis on plant uptime.
Pump testing has previously been addressed in a number of documents, including The
Hydraulic Institute [1] (testing), API 610 [2] (centrifugal pumps), and API 676 [3]
(rotary gear pumps). But, the test procedures covered in these documents focus primarily on testing at the pump manufacturers' own facilities. Such tests are accurate, repeatable, and reliable, but are difficult to duplicate in the field, where access to specialized
test instrumentation is often difficult or impractical. For example, torque meters are
routinely used by manufacturers for testing. These devices, which can measure torque
and speed, and can perform internal conversion to calculate power, are only used temporarily as auxiliary devices, and are not installed in the field between the pump and a
driver. Therefore, a user cannot readily measure pump input torque to calculate the
horsepower, even if the rotational shaft speed is known. Reading the motor current,
however, is relatively straightforward, and so, for field operators, a method that converts
from current to power, even if some accuracy is sacrificed, would be useful. Another
example is a requirement of a certain length of piping at the pump inlet, as well as
before measuring devices (gauges, flow meters). Rarely, if ever, do such "perfect"
accommodations exist in the field. Obviously, the accuracy of measurements cannot be
expected to be as good as at the manufacturers' test facilities.
The need to differentiate between the more accurate pump manufacturer test facilities
and field testing methods has been recognized in the past, in AlChE Equipment Testing
Procedures for Centrifugal and Rotary Positive Displacement Pumps, [4,5]. Reading
them now, these documents are not outdated, but do have two major shortcomings.
First, they are focused on rotary pumps, and for Newtonian liquids only. Second, their
style is too "academic" for use by those who operate the pumps. A complete revision
and rewrite of the field testing procedure to include the positive displacement pump
types now commonly used at chemical plants and related facilities is long overdue.
Since the introduction of the first field-testing procedure in 1968, a large number of
new chemicals have been introduced by the rapidly expanding industry. NonNewtonian fluids can no longer be considered an exception, and pump-testing procedures must incorporate such cases. There are numerous examples of pumpage that is
not liquid, but is a fluid in a more general sense. Paper pulp, slurries, waste sludge, and
adhesives are all examples of fluids that, at least by appearance, do not resemble a liquid
at all.
1
AlChE Equipment Testing Procedure
The style of this Procedure is simple and practical. It is hoped that it would be easy
and interesting to read, and could be useful for the internal training of plant personnel,
as well as for expanding the general existing literature on pump fundamentals and reliability, such as [6], [7], [8].
2
Positive Displacement Pumps
200.0 Extended Definitions of Major Terms, with Explanations,
Conversion Factors, and Nomenclature
Note: All calculations and data in this document are measured using common sets of U.S. units. To convert
to metric units, refer to the conversion factors given at the end of this section. To make the document more
useful, definitions are accompanied by short explanations relating to pump operating principles.
200.1
Positive Displacement (PD) Pump
In common terms, a pump is thought of as a device from "flange-to-flange," that is,
between the suction and discharge flanges, thus differentiating it from the "system," which
would include the motor, coupling, baseplate, tanks, connecting piping, and controls. A PD
pump can be thought of as a "flow generator," as compared to a centrifugal pump, which
can be imagined as a "pressure (or head) generator."
200.2
Fluid versus Liquid
200.3
Flow
200.4
Pressure
200.5
Net Positive Inlet Pressure (NPIP)
A fluid is a substance that is unable to resist even the slightest amount of shear without
flowing. Liquids, gases, and vapors are fluids, but liquids are practically incompressible,
except at very high pressures.
This is a volume of fluid per unit of time. The ideal flow disregards "slip," or the portion
of flow that "slips" back through the internal clearances from discharge side to suction,
driven by the differential pressure across the pump. The net flow is what actually comes
out from the pump exit into the discharge pipe. Another term often used interchangeably
with flow is "capacity."
There are discharge, suction, and differential pressure terms. It is very important to specify
gauge (psig), absolute (psia), or differential (psid) pressure; mistakes are common, especially
for cases of suction vacuum. Actual available suction pressure must be greater than the
minimum required suction pressure, in order to avoid adverse effects on pump operation,
such as flow loss, cavitation, noise, vibration, and so forth.
The subject of NPIP is analogous to that of NPSH (net positive suction head) in centrifugal pumps. Traditionally, however, inlet conditions for positive displacement pumps have
been defined in pressure terms, rather then in head terms. NPSH, given in feet of liquid
(or meters if metric units are used), is basically the pump inlet head minus the head equivalent to vapor pressure of the pumped fluid. Since density has already been used in converting pressure terms into head, NPSHR (required NPSH for a centrifugal pump) is not a
function of density (or specific gravity). It depends on the inlet geometry of the centrifugal
pump, and rotating speed (approximately as a square of rpm).
3
AlChE Equipment Testing Procedure
NPIP, on the other hand, is the pump inlet pressure minus the fluid vapor pressures. PD
pumps typically operate in systems with low inlet velocities. In these cases, the velocity
head portion (dynamic head) has historically been ignored.
NPIPR, with the "R" signifying "pump required," is the difference between the inlet pressure and the vapor pressure—corrected to the centerline of the pump inlet port—necessary for the pump to operate without a reduction in flow. The Hydraulic Institute defines
the minimum required pressure (or equivalent NPIPR) as such where 5% of the flow
reduction occurs due to cavitation.
For positive displacement pumps, any increase in NPIPA, with the "A" signifying "pump
available," has no effect on volumetric efficiency, as long as NPIPA is above the NPIPR.
Low values of NPIPA may result not only in flow reduction, but also in significant pressure
spikes, vibrations, noise, and possible damage to the pump.
200.6
Power
200.7
Efficiency
Power is defined as energy per unit of time. The gross power delivered by the driver to the
pump is called break horsepower (BHP), and net power delivered to fluid by the pump is
called hydraulic, orfluid power (FHP), and can be calculated as the product of the differential
pressure times theoretical flow, with the appropriate coefficient, plus internal viscous
power losses. The difference between the break and hydraulic power is due to the internal
losses, or the sum of mechanical and volumetric losses.
Historically, an overall pump efficiency assessment has not been as widely used with PD
pumps as with centrifugal pumps. Volumetric efficiency has been a much more common
method of comparison between different designs and applications. Positive displacement
pumps are inherently constant flow machines with regard to differential pressure. In
theory, a constant volume of fluid is "displaced" with every rotation, stroke, or cycle—
hence the name. However, because of the internal clearances, a certain amount of fluid
"slips" back from the discharge side to suction. This slip depends on the lateral and radial
clearances, and on the overall differential pressure which drives it. The higher the viscosity
of the fluid, the more it resists the slip. The net actual flow is the difference between the
ideal, or theoretical flow, and the slip:
Qa = Q o - Q s l i p
(200.7.1)
which can be also expressed in terms of volumetric efficiency:
4
Positive Displacement Pumps
The overall efficiency, often called "mechanical efficiency" in PD pumps, is a ratio of useful hydraulic power (FHP) transmitted to the fluid exiting the pump, to a total power
(BHP) absorbed by the pump:
(200.7.2)
200.8
Torque
200.9
Viscosity
200.10
Specific Gravity
200.11
Revolutions per Minute (rpms)
Torque is a measure of the machine's ability to move the resisting loads—power divided by
rotating speed in rpm, with an appropriate coefficient, depending on die units. For the same
power, the torque is greater at low speed. For example, a speed reducer increases torque.
Viscosity is defined as a fluid property that characterizes its ability to resist motion.
Dynamic viscosity is a coefficient between the fluid shear rate and shear stress. Kinematic
viscosity is equal to dynamic viscosity divided by the specific gravity. This is a major
parameter influencing pump operation. Pump power goes up with viscosity to overcome
the internal hydraulic viscous drag. Suction conditions become more demanding with
increased viscosity, reflecting the ability of the fluid to get to the pump suction port, and
fill its displacement mechanism (gears, screws, etc.). Kinematic viscosity is measured in
centistokes (cSt); dynamic viscosity is measured in centipoise (cP). Other common units of
dynamic viscosity are Saybolt Seconds Universal (SSU). Refer to charts for exact conversions, but a good rule of thumb is cP x 5 = SSU, for viscosity above approximately 50 cP
This is a ratio of fluid density to water density at 60 °F at atmospheric pressure.
In the 1980's, it became common and fashionable to use smaller, faster running pumps, as
opposed to larger, slower running pumps, for obvious cost reasons. However, with speed
came trouble, as many maintenance and reliability plant personnel discovered. A faster
running pump requires more suction pressure, and also wears out disproportionately faster.
Today, it is important to consider not only initial cost, but also wear, suction requirements,
vibration, and so forth, to strike a balance between speed and reliability, for a given flow
requirements.
200.12
Extended Definitions
Q
Pump net flow, gpm
QQ
Pump theoretical flow, disregarding slip, gpm
Q s |jp
Pump slip, gpm.
BHP
Pump input power, hp
5
AlChE Equipment Testing Procedure
rpm
Ps
Pump shaft rotational speed, revolutions per minute
Pump suction pressure (usually in absolute units, psia or
psig)
Pd
Ap
Pump discharge pressure (usually gauge units, psig)
v
Kinematic viscosity of the pumped fluid, centistokes
\i
Dynamic viscosity, centipoises (cP)
Ps
Minimum required suction pressure
Differential pressure (psi or psid)
(expressed in absolute units, psia)
^vol
Volumetric efficiency
^mech
Mechanical efficiency
Overall efficiency
PF
Motor power factor
'H motor
Motor efficiency
T
Torque, in lbs.
Table 1: Basic conversion factors
Flow
Convert from
GPM (US)
GPM (US)
Pressure and head
Divide by
4.403
15.9
Convert to
m3/HR
liters/sec
Convert from
psi
psi
psi
Divide by
14.7
14.5
145
Convert to
Atm
Bars
MPa
Convert from
HP
Multiply by
0.746
Convert to
KW
If needed, other conversion formulas may be found in standard engineering texts and data
tables.
6
Positive Displacement Pumps
300.0 Types of Pumps Covered in this Procedure
The two major classes of positive displacement pumps are rotary and reciprocating. In
industry, where this AlChE procedure mostly applies, the majority of applications are handled by the following pump types, which form the basis of this procedure:
a) Rotary (gear, lobe, screw, and vane)
b) Progressive Cavity
c) Diaphragm
d) Piston/Plunger
Figure 1: Types of positive displacement pumps
Used courtesy of The Hydraulic Institute (1)
7
AlChE Equipment Testing Procedure
,—, Closed coupled
Single or Two Stage
1
End Suction
(Including submerslbles)
1
In-line
1
Separately coupled
Single and T w o Stage"
«0
_
3 _
O
Impeller between
bearings
.
_
. .
, .
i
Separately coupled __J
Single and Two Stage I
—
Separately coupled
Multistage
1 Radial (Vert.) Split case
,
ss.
Vertical type
s ingle and Multistage
i
Turbine type
!
— Regenerative
turblr e
In-line
Frame mounted
Centering support
API 610
_
Frame mounted
Ansl B:73.1
Wet Pit Volute
Axial flow Impeller/propeller
Volute type Hor/Vert
1 Axial (Hor.) Split case
v
'
1 Radial (Vert.) Split case
Axial (Hor.) Split case
Deep well turbine
Including Submerslbles
Barrel or can pump
Short setting or closed
coupled
Axial flow Impeller (propeller)
or Mixed flow type (horizontal)
or vertical
| |
Single Stage
Two Stage
>—i Impeller between bearings
Reversible centrifugals
Sp
Rotating Casing
Figure 2: Types of kinetic (centrifugal) pumps
These pump types are not covered in this standard, and are shown here for information purposes only.
Used courtesy of The Hydraulic Institute.
The simplified sketches that appear on page 7 and above describe these popular pump
types, with a brief explanation of their principles of operation. The sketches are used
courtesy of The Hydraulic Institute.
300.1
Gear Pumps
Gear pumps may be external or internal in design. Internal designs may have a crescent
between gears. Inlet fluid fills the cavities between gear teeth and the casing. Fluid is then
moved circumferentially to the outlet port, where it is discharged. Radial hydraulic forces
are unbalanced, and bearings, or bushings, are required to support the rotors. Since gears
touch, the materials of construction should be preferably dissimilar, especially for low-viscosity applications. Stainless steel drive gear, if running against stainless idler gear, tend to
gall and should not be used, especially for low-viscosity or poorly lubricating fluids. It is
better to run stainless steel drive gear against the nonmetallic (e.g. Teflon) idler gear for
such applications, and this is typically done in industry.
Positive Displacement Pumps
Figure 3 and 4: External gear pump (left) and Internal gear pump (right)
300.2
Lobe Pumps
Figure 5: Lobe pump internals
Lobe pumps are similar to gear pumps, except that the lobes are not in contact, and a timing mechanism is used to transfer the rotation of the drive rotor to the idler. The number
of lobes varies between 1 and 5. A three-lobe design is shown above.
300.3
Multiple Screw Pumps
Figures 6 and 7: Two-screw pump (left) and Three-screw pump (right)
9
AlChE Equipment Testing Procedure
These pumps are usually of the two-screw timed, or three-screw un-timed design. Inlet
fluid fills the cavities between screws and the casing or liner. Fluid is moved axially to the
outlet port, where it is discharged. Radial forces are unbalanced in the two-screw pump,
but are balanced in the three-screw design. Technically, The Hydraulic Institute classifies
Progressive Cavity pumps as a single-screw design variation. However, there is a much
greater similarity between the two- and three-screw designs than between either one of
them and a progressive cavity design. For this reason, a progressive cavity design is treated
separately in this Procedure (see page 11).
300.4
Vane Pumps
Figure 8. Vane pump
Vanes, which may be in the form of blades, buckets, rollers, or slippers, cooperate with a
cam action to allow liquid to fill the cavity formed between the vane and the casing liner.
The fluid is moved circumferentially to the outlet port, where it is discharged. The vane(s)
can be stationary or rotating. Radial hydraulic forces may be balanced or unbalanced.
Some designs provide variable flow by varying the cam action eccentricity. Illustrated
above in Figure 8 is a vane-in-rotor, constant displacement, unbalanced vane pump design.
10
Positive Displacement Pumps
300.5
Progressive Cavity pumps
Figure 9. Progressive Cavity pump
Progressive cavity pumps are a unique type of positive displacement pump. The simplest
PC pumps have a single-threaded screw, called a rotor, turning inside a double-threaded
nut called a stator. As the rotor rotates inside the stator, two cavities form at the suction
end, with one cavity opening at the same rate as the other cavity is closing. The cavities
progress (hence the name), from one end of the stator to the other.
In most PC pumps, the stator is made with an elastomeric material (rubber, Teflon, etc.),
that fits on the rotor with a compressive fit. The metallic rotor can be plated in order to
increase wear resistance. This compressive fit between the rotor and stator creates seal
lines where the two components contact. The seal lines keep the cavities separated as they
progress through the pump.
Progressive cavity pumps are known for their ability to self prime, suction lift up to 28 feet,
and handle shear-sensitive and high-viscosity materials, abrasive fluids, as well as fluids
with large particles in suspension.
300.6
Diaphragm Pumps
Figure 10: Diaphragm pump in operation
n
AlChE Equipment Testing Procedure
The Hydraulic Institute groups diaphragm pumps with controlled volume-type pumps.
Hydraulically or mechanically actuated diaphragms displace the fluid from suction to discharge side and are aided by the valving mechanism, which allows fluid to enter the pump
chamber during the suction stroke, and displaces it during the discharge stroke.
300.7 Piston/Plunger Pumps
Figure 11. Piston pump cross-section
Piston/plunger pumps are of the reciprocating type. T h e liquid chamber is alternatively
connected to the suction and discharge sides, with a system of internal valving. These
pumps are particularly well suited for extremely high pressures.
12
Positive Displacement Pumps
400.0 GENERAL NOTES ON TEST PREPARATION LOGISTICS—
Instruments and Methods of Measurements
400.1 Flow
For positive displacement pumps, the key measured parameter is flow. For chemical plants,
the most common way to measure flow is with a flow meter. Other simple methods, such
as known volume vessel plus a stopwatch, or other open-end measurements, are not practical for the hazardous environment of a chemical plant. For better accuracy, flow meters
should be periodically cleaned and calibrated. In theory, the viscosity of the measured
fluid must be similar to the calibration fluid, but in practice there can be a wide variation
of viscosity (+/- 1000 cP), and the flow measurement error would be within + / - 2%,
which is acceptable for most field tests.
Because the theoretical flow of positive displacement pumps is directly proportional to
speed, another simple method is to measure the pump shaft rpm, and multiply it by the
pump unit flow (gallons-per-revolution). The unit flow is constant for a given pump and
can be calculated from the pump performance curve at zero differential pressure. The net
(actual) flow is the difference between the theoretical (zero pressure differential) flow and
slip. Slip can be obtained from the pump curve at a given differential pressure and fluid
viscosity. In practice, for high-viscosity fluids (over 100 cP) and/or low differential pressures (less than 20 psi), the slip can be neglected and the net flow simply calculated as
measured rpm times the unit flow from the curve.
Note: Pump rpm can be measured using a tachometer or a strobe light. It may also be assumed, with some
accuracy, to be close to the motor nameplate value, adjusted by the gearbox ratio if a gearbox is present.
It is always a good practice to conduct a pump field test soon after it has been installed, in
order to generate a baseline field-specific curve for future test comparisons.
400.2
Pressure
400.3
Power and Efficiency
A common mistake is to assume the pressure at the pump inlet flange from the known
pressure, such as tank level, and adjust by calculating the losses, or by assuming losses are
negligible. This approach is particularly wrong for calculating the suction pressure, as collapsed filters, debris, solids, or other obstructions can make the pressure estimates completely invalid. The only reliable way is to install and read gauges and measure the pressure in suction and discharge pipes as close to the pump flanges as possible.
The most practical way to measure pump input power is to measure the motor's electric
current and voltage. The available shaft power can then be calculated as:
KW = I x V x ri
t
/ 1000, for 1-phase motors
13
(400.3.1)
AlChE Equipment Testing Procedure
K W = I x V x 1.732 x r|
motor
x PF / 1000, for 3-phase motors
BHP = K W / 0.746
(400.3.2)
(400.3.3)
The power factor and motor efficiency can normally be obtained from the motor manufacturer, at least for full load conditions. Both of these items va ry widely from motor to motor,
and with changes in load on the motor. If power factor and efficiency cannot be accurately
determined at the motor's operating conditions, it may not be possible to accurately determine the pump's input power. Checking that the motor current is not above the nameplaterated current at pump operating conditions may be the only possible test for input power. If
there is a gear reducer, or any other device that absorbs motor output power, coupled between
the motor and the pump, its power losses must be estimated. This is often available from the
manufacturer. If the pump and motor are directly coupled together, motor output power can
be taken as pump input power.
Below are power factor multipliers recommended for three-phase Toshiba motors. For factors of particular equipment, contact the equipment manufacturer. In most cases, the
power factor and motor efficiency are not readily known, and obtaining the exact values is
impractical. However, as an approximation, the efficiency of the electric motor can be
assumed as 95%, and the power factor is also 0.95, such that their product is approximately 0.90. As long as the performance does not change with time, such approximation would
still serve a valid purpose.
Finally, it is recommended the information be reviewed and confirmed, as the values for
motor efficiency and power factor both seem to be the highest obtainable. These high values are usually reserved for motors in the 200 horsepower and above range. This would
indicate a lower horse power motor would be required in the estimating stages than would
actually be needed in operation. The key to field testing is simplicity and fully utilizing the
available tools.
Table 2. Typical power factor correction table
© T.M Eiiifjson
1398
14
Positive Displacement Pumps
The hydraulic (net) pump fluid power is:
FHP = (AP x Q Q / 1714) + viscous losses
(400.3.4)
The current to calculate the K W must be read at actual operating differential pressure.
The overall pump efficiency is then:
TI = FHP / BHP
400.4
(400.3.5)
Temperature
In the field, fluid temperature and the pump skin temperature are determined to make
sure they are not excessive, and thus affecting the pump internal clearances. For certain
types of pumps, especially the progressive cavity type, the internal clearances change dramatically with temperature, effecting flow slip, mechanical friction, efficiency, and pump
life.
15
AlChE Equipment Testing Procedure
500.0 TESTING ROTARY PUMPS (Gear, Multiple Screw, Lobe and
Vane Pumps)
The objective of a test is to measure the performance of the pump under a known set of
conditions. Pump performance may be defined as a group of six interrelated variables:
flow through the pump (Q), power input (BHP), drive shaft speed (rpm), pressure at the
suction port (ps), pressure at the discharge port (p^), and the kinematic viscosity of the liquid being pumped (v). Most of the time, flow and power are considered to be the dependent variables, and the others are independent variables.
The first step in any field pump test is to decide which variables will be set, and which
ones will be measured as the results. When the test is performed in the field, some of the
variables will be difficult, or impossible to change from the normal values determined by
the system in which the pump is installed. For example, a constant speed motor without a
variable speed control cannot operate at different speeds for the test, so in this case shaft
speed (rpm) would be one of the independent variables, or one of the values to be set,
instead of measured. With this in mind, there are two standardized types of pump tests
commonly used in factory testing that may not be suitable for field-testing conditions without some modifications. For these cases, the example test report form in Table 3 may be
used to design a new test by filling in the quantities that will not be changed, or c a n n o t
be changed, and measuring the other quantities.
All applicable plant safety rules should be reviewed and followed whenever a facility
attempts to test any rotating piece of equipment. In some cases it may be advisable to
complete a plant safety review prior to attempting the test. Finally, make sure that, when
the test is conducted, the operating team is, at minimum, aware of your plans and is in
communication with you.
Table 3. Performance test report form
(also used for the suction test, with some parameters omitted)
16
Positive Displacement Pumps
501.0
Test Equipment
Each of the variables should have an instrument to record its quantity during the test.
Section 400 presents general notes on instrumentation. Even fixed variables, such as the
speed of a fixed speed electric motor, should be recorded during the test to ensure that no
unknown influences are introduced. For example, motor speed tends to decrease as the
motor load increases, and this should be observed and recorded during the test.
501.1 Shaft Speed
There are many types of tachometers that can be used on either the
pump or motor shaft, as long as a device connects the two shafts and
maintains a constant speed ratio between them. If a device, such as
an eddy current drive, is used that varies the speed ratio between the
shafts, the tachometer must be used only on the pump shaft. The
tachometer should be accurate to within 2% at the test speeds. A
small change in speed can make a large difference in the performance
of a large, low-speed pump. A strobe light is less accurate, although it
is acceptable.
501.2 Suction and Discharge Pressures
Pressure gauges or transducers should be accurate to within 5% of
the test pressures, and the test pressure should be between 20% and
80% of a gauge's range. Suction and discharge pressure gauges, or
transducers, usually have different pressure ranges. Suction pressure is
usually recorded in psia (absolute) units, and discharge pressure in
psig units, (psia = psig + 14.7).
501.3 Fluid Viscosity at Range of Temperatures
The simplest way to obtain an idea of viscosity during a pump test is
to measure the liquid temperature and then find the viscosity from a
chart of temperature versus viscosity for the test liquid. These charts
are available for many liquids in reference books, as well as from the
manufacturer. If no chart is available, a test with a viscometer at several different temperatures will allow you to create such a chart. The
thermometer or thermocouple used to measure the temperature
should be accurate to within 5% at the test temperature.
If the fluid to be pumped is Newtonian, defined as having a viscosity
constant with changing shear rate, it is acceptable to test a range of
viscosities by using several liquids that have different viscosities at the
same temperature. This is often easier than heating or cooling a single fluid to obtain a range of viscosity. Positive displacement pumps
are not very sensitive to changes in liquid density or specific gravity,
so one liquid can substitute for another in the test. This must not be
done, however, if the liquid is non-Newtonian (thixotropic or dila17
AlChE Equipment Testing Procedure
tant). If a pump is intended to operate on a non-Newtonian liquid,
the test should only be performed using that liquid. Dilatant liquids,
which increase in viscosity as the shear rate increases, are especially
tricky because a test on a Newtonian liquid would understate the necessary input power and the pump's driver could be overloaded in
operation.
When a viscous fluid is involved, which is quite common with PD
pumps, there are two persistent problems: establishing a reasonably
accurate system curve at which the fluid will be pumped at its actual
viscosity. Emphasis is placed on the "actual viscosity" that typically is
a function of temperature. Start-up conditions frequently result in
lower temperatures and higher viscosities than at operating temperatures, and in turn, higher horsepower than anticipated. Unless
motors, pumps, and relief systems are selected appropriately this can
cause a major delay in the start-up of a new system, or in conducting
tests that may pass through auxiliary piping.
Pump vendors have compiled technical manuals that graphically
establish the relationship between pressure loss, viscosity, and pipe
size. Calculations for precise values are often laborious. Consequently,
estimates are frequently employed. Such methods approximate performance and do not generate a true bench test performance curve.
501.4 Flow Rate
A positive displacement pump moves a fixed volume for each revolution of the drive shaft; it is volumetric flow rate, which is most closely
tied to pump performance. It is possible to measure mass flow and
divide by the density of the liquid. Placing a flow meter in line with
the pump is the simplest method, but measuring the time to pump
out or fill a tank of known volume may also be used, if possible.
501.5 Input Power
In a field test it will rarely be possible to put a torque meter between
the pump and driver to measure pump-input power directly. Usually,
the best available option is to measure the current and voltage going
into an electric motor. The power output of a three-phase AC motor
can be calculated from the formulae given in Section 400.3.
502.0 Standardized Tests
502.1 Performance Test
The purpose of this test is to generate graphs of flow rate versus differential (discharge minus suction) pressure, and also input power versus differential pressure, with a constant liquid viscosity, suction pressure, and shaft speed. In addition to the test equipment listed in
18
Positive Displacement Pumps
Section 400, this test requires a valve near the outlet port of the
pump that can be used to throttle the flow to increase the pressure at
the pump. The highest pressure during the test should not be more
than 90% of the opening pressure of any relief valve in the system or
in the pump. Any restrictions in the system downstream of the pump
should be reduced as much as possible to reach lower pressures at the
pump during the test. See Figure 12 for a diagram of a typical installation and field-test setup.
Figure 12: Installation and set-up for pump performance field test
Estimate the range of discharge pressures to be tested, and divide the
maximum expected differential pressure by five (i.e., six points test).
The result is the amount to increase the discharge pressure by the
next test point.
To begin, operate the pump with the throttling valve open, and
record the values of all six variables. Close the discharge throttling
valve slowly, and record all six variables. Record all six points in Table
3, increasing pressure incrementally. Plot the data in the form of
graphs, as shown in Figure 13.
19
AlChE Equipment Testing Procedure
* If the current is measured instead, calculate and plot power using formulae in Section 400.
Figure 13: Example of pump performance curves
502.2 Minimum Required Suction Pressure Test (MRSP)
This test determines the effect of changing suction pressure on pump
performance. Below a certain pressure, the flow out of the pump will
drop dramatically. Above this pressure, the flow asymptotically
approaches the theoretical flow of the pump, as defined by The
Hydraulic Institute. The suction pressure that causes the flow to drop
5% below this asymptote is considered to be the pump's minimum
required suction pressure. This test requires a throttling valve in the
20
Positive Displacement Pumps
suction piping near the pump, as well as another valve on the discharge side.
At the beginning of the test, all valves on the discharge side of the
pump should be open in order to lower the pump's discharge pressure
as much as possible. The pump's supply tank should be full or, if it is
portable, raised as high above the pump as possible. This will increase
the pressure at the pump's suction as much as possible, so that during
the test, the flow will be as close as possible to the theoretical ( Q J
when the suction valve is open. Figure 14 shows the test setup, and
Figure 15 shows the outcome of the test in a graph of flow versus
suction pressure. The same table (Table 3) can be used with only suction pressure and the flow recorded, or other parameters of interest
can be noted as well. During this test, shaft speed, discharge pressure,
and liquid viscosity are held constant. Input power does not change
too much, and it is usually not measured for this test.
Vent
Tank Overflow
Discharge
Tank
■©■
«
Flow Meter
Relief Valve
Motor
If*
Tachometer
ps
£ y$-
f4Throttling Valve
Supply Tank
Throttling Valve
Pump
testing for p .illlin>
Figure 14: Minimum suction pressure test set-up
Operate the pump with both throttling valves open, and record the
values of all of the variables. Start slowly, closing the suction sidethrottling valve until the suction pressure drops 2 psi below its previous value. Record the values of all the variables again. Repeat this
process using increments of 2 psi in the suction pressure until the
pump's flow has dropped to 90% of what it was at the beginning of
21
AlChE Equipment Testing Procedure
the test. Do not operate the pump in this condition for any longer
than is necessary to record the data, and never close the suction side
valve all the way while the pump is running. Plot the flow at the various pressures recorded for this test in Table 3, in the form of the
graph in Figure 15.
Note: If increased noise or vibrations are encountered, do not operate beyond that
point. Minimum required suction pressure, in this case, would be determined not
by the 5% flow decrease rule, but by the mechanical and structural limitations of
the pump oryour system. Discuss these results with the pump manufacturer. If the
minimum required suction pressure determined is significantly different from the
manufacturer's catalog value, pump and/or system troubleshooting might be advis able.
Figure 15: Minimum suction pressure results
503.0 Other Tests
There are many other tests that may be performed on pumps other than the two
described above. The three most common are sound pressure level, vibration, and temperature measurements.
22
Positive Displacement Pumps
503.1 Sound Pressure Level
Sound pressure level measurements may be taken at the pump's normal operating condition, or may be made in conjunction with one of
the performance tests above to give a record of sound pressure levels
across a wide range of conditions. The microphone locations for the
test should be approximately 5 feet above the floor or walkway nearest the pump. One reading should be taken from each end of the
pump and motor set, approximately 3 feet away from the pump or
motor housing. Other readings should be taken at the pump's inlet
and discharge ports and on both sides of the motor. All of these readings are taken 5 feet above the floor. If the pump and motor are
mounted vertically, take a reading at four positions, 90 degrees apart,
around the pump. These should all be taken 5 feet above the floor,
and 3 feet away from the nearest part of the pump or motor housing.
Note that the environment around the pump, such as acoustically
reflective or absorbent surfaces, can have a great influence on the
sound pressure measured value. Other equipment operating nearby
will also influence sound pressure measurements.
503.2 Vibrations and Temperature
Vibration and temperature measurements are usually taken for maintenance reasons, and can be used to predict an upcoming failure so
the problem can be corrected before it occurs. To do this, it is very
important to take baseline measurements before any problems occur.
Then changes in these quantities (with time) can signal an upcoming
problem. Vibration and temperature measurements are normally
taken at a pump's normal operating condition. The key parts of the
pump that affect its reliability must be determined, and the measurements taken as close as possible to these components. Measurements
are usually taken on the surface of the pump housing; instrumentation can be put inside the pump before installation to monitor particularly critical components. The most commonly monitored components are bearings, rotors, and shaft seals. Table 4 can be used to
detect changes by recording pump parameter trends with time.
However, the basic parameters, such as speed, operating pressure,
pumped liquid, and so forth, must remain the same, in order to
obtain a valid comparison of the parameters that are truly changing
with time.
504.0 Test Process Example
Figure 16 is an illustration of a rotary gear pump installed at a chemical plant on an acid
transfer application. A magnetic flow meter was present further downstream, past the
check valve. It was equipped with an electronic data port and connected to the plant
23
AlChE Equipment Testing Procedure
Table 4: Time trending of basic parameters
control room, where operators could read the pump flow directly. There was a gearbox
between the motor and a pump, with a resultant pump speed of 1000 rpm. The pump
took suction from the vented tank, but with a slightly pressurized nitrogen blanket, about
10 psig.
The maximum discharge pressure was below 80 psig. The normal rated operating point
was 20 gpm at 50 psig discharge pressure, although a pump manufacturer catalog allowed
pump maximum differential pressure to 100 psig at the given fluid viscosity and pump
speed.
Unfortunately, there were no pressure gauges installed near the pump. Gauges had to be
added near the existing vent/drain connections. This was considered sufficiently close to
the pump inlet and discharge flanges. Shaft speed was monitored by a handheld tachometer reading the signal from the translucent reflective tape mounted near the coupling.
Motor current was monitored from the operator's console in the control room. Fluid viscosity (approximately 40 cP) was measured at the ambient temperature of 80 °F before the
test. Specific gravity could not be measured, but was assumed to be 1.2, per the pump
datasheet.
504.1 Performance Test
In accordance with a six-point test procedure, described in section
502, the incremental pressure steps were approximately established
as:
(504.1.1)
During the test these increments were actually held between 15 and
20 psi.
24
Positive Displacement Pumps
Figure 16. Sample installation for a rotary pump test
The operating personnel were notified that the test was about to start.
Discharge and suction valves were opened. It was verified that the
pump suction was flooded. The pump was started and operated for
about 10 minutes to stabilize the process. Air was purged from the
system and the instruments. The discharge valve was throttled slowly
and the data were recorded in the following table.
25
AlChE Equipment Testing Procedure
Table 5: Raw performance data for rotary pump test
Speed
Test Point
#
rpm
1003
1001
998
998
995
997
1
2
3
4
5
6
Suction
Pressure
psia
22
22
21
22
21
22
Discharge
Pressure
psig
9
20
37
57
74
94
Flow
QPm
23.7
23.5
22.5
22
21.7
20.8
Current Temperature
Amps
0.7
0.8
1.7
2
3.1
3.5
Comments
78
78
78
78
79
79
For the three-phase 3 Hp electric motor, rated at 440V, the horsepower was calculated as:
KW = I x V x 1.732 x PF x E F F m o t o r /1000
Voltage at the motor leads was measured as 465V This did not change significantly during
the test. The power factor times the motor efficiency was assumed to be 0.9, because the
motor performance curve was not available.
BHP = K W x 0.746 = I x (465 x 1.732 x 0.9 x 0.746 / 1000) = I x 0.54.
The results of the test, listed in Table 6, were then plotted. The resultant performance
curve, shown in Figure 17, was compared with the manufacturer's catalog curve (Figure 18)
and determined to be within close agreement.
Table 6: Calculated parameters for performance test
Test Point
#
1
2
3
4
5
6
Delta P
(Pd - Ps)
psia
1.7
12.7
30.7
49.7
67.7
86.7
Flow
Bhp
gpm
23.7
23.5
22.5
22.0
21.7
20.8
0.40
0.45
0.94
1.10
1.70
1.90
Comments
Note: A manufacturer's catalog may not always have the curves at the exact viscosity, and some interpola tion may be required. In this example, the test curvesfor the 40 cPfluid correlate reasonably between the
published curves for 1 cP and 200 cP, as shown in Figure 18.
26
Positive Displacement Pumps
Figure 17: Performance curve drawn from data in Table 6
504.2 Observations:
1) The pump performed as expected. At the normal operating point,
there was sufficient flow (20.5 gpm). This was slightly above the
required 20 gpm. Qgj- = 23.7-20.5 is approximately 3 gpm.
2) No abnormal noises or vibrations were observed.
3) There was no problem with the motor. Amperage readings throughout the test did not exceed the motor's nameplate full-load amps. In
addition, observations did not detect excessive motor temperature
rise, which would have been an indication of overload. At the maximum operating pressure (80 psig), the pump requires 1.8 hp, which is
below the motor nameplate rating of 3 hp. An oversized motor had
been selected in anticipation of future applications for heavier liquids.
4) It is usually not a practice to calculate efficiencies for PD pumps, but,
if desired, the calculation would be as follows:
Volumetric efficiency at the rated point:
27
AlChE Equipment Testing Procedure
Overall efficiency at the rated point:
Figure 18: Performance comparison to the manufacturer's catalog curve
28
Positive Displacement Pumps
504.3 Minimum Required Suction Pressure Test
The pump was operated again with open discharge and suction
valves and allowed to stabilize for five minutes. The suction valve was
then slowly closed, and data were recorded at different pressure
points. See Table 7 for results. The test was started at 4 psi intervals,
and increments of pressure were reduced as the flow started to
decrease.
Test Point
Pressure
(Ps)
Flow
Comments
#
psia
qpm
1
2
3
4
5
6
7
8
9
10
11
22
18
15
12
10
8
6
5
4
3
2
23.5
Start up of the test
23.5
Estimated 5% loss @ 22.3 gpm
23.5
23.4
23.3
23.2
23.1
Cavitation "crackling" has started
23.0
Cavrtation more intense at this point
22.8
22.4
Near Ps min (5% flow drop at this point)
Beyond 5%, sever, loud noise experienced:
-
21.4
-
-
-
The pump should not be kept at this operating condition for long
Return to normal operating condition by opening the suction valve.
Table 7: Minimum required suction pressure test (Field data)
The results from Table 7 were then plotted in Figure 19.
29
AlChE Equipment Testing Procedure
Figure 19: Minimum required suction pressure test graph
For data in Table 7
504.4 Observations:
1. Minimum required suction pressure for cavitation-free operation is
P'suction = 2.-7 psia at 1000 rpm and 40 cP.
2. Some cavitation "crackling" noise was observed at approximately 6
psia. Since the installation had plenty of available suction pressure,
about 22 psia (7.3 psig), the pump should not experience future cavitation problems.
3. The results are applicable only to the given pump, operating at the
given speed and pumping similar viscosity material. At other speeds
or viscosities, the value of the minimum required suction pressure
would be different and would need to be established by performing a
test procedure similar to that outlined above.
504.5 Other Tests
Sound, vibrations, or other parameters were not recorded in these
tests, but could be easily accommodated if required. Such extended
tests are usually performed to troubleshoot a pump/system to pinpoint internal problems, such as mechanical rub, cavitation, or failing
bearings, which can be determined by using a frequency analysis.
30
Positive Displacement Pumps
600.0 Progressive Cavity Pump Testing
Progressive cavity pumps are a unique type of rotary positive displacement pump. The
simplest form of a progressive cavity pump is a single-threaded helical rotor turning inside
a double-threaded helical stator. In most progressive cavity pumps the stator is made with
an elastomeric material and fits on the rotor with a compressive fit. The contact between
the rotor and stator creates a seal that results in the formation of cavities. The geometry of
the parts is such that, as the rotor turns through one complete rotation, two cavities are
formed. One cavity closes at the same rate as the second cavity opens, progressing from
the suction to the discharge end of the stator, thus giving it the name "progressive cavity
pumps."
Progressive cavity pumps can generally be tested in the field in accordance with the procedures outlined in Section 400. However, due to the wide range of functions for which progressive cavity pumps can be applied, the unique characteristics of the pumped fluid must
be considered. In many applications, pump testing is performed with water and the results
achieved with water must be correlated to the actual process fluid.
Precautions:
Before operating progressive cavity pumps, it is essential that the system be reviewed to
ensure that the suction and discharge lines to the pump are not obstructed. Progressive cavity pumps cannot
operate dry or withoutfluid passing through them for prolonged periods of time without damaging the
pump. Similarly, progressive cavity pumps cannot be operated against a closed or obstructed discharge line
without possible damage to the pump and system, and possible injury to personnel.
The pressure capability of progressive cavity pumps is a function of the number of stages,
pump size, pump speed, and fluid pumped. It is recommended that the operating characteristics of the particular pump model be known before operating the pump.
601.0
Test Equipment
The instrumentation described in paragraph 500.0 (Test Equipment) is generally acceptable for use with progressive cavity pumps, with some additional consideration given to the
unique characteristics and capabilities of this pump design.
601.1 Shaft Speed
Progressive cavity pumps typically operate at slower speeds than other
types of pumps. Although the use of mechanical shaft speed indicators is preferred, properly calibrated strobe tachometers are also
acceptable. In many applications, a speed indicator is included as part
of the drive package and, when properly calibrated, are acceptable
for accurately determining shaft speed.
31
AlChE Equipment Testing Procedure
601.2 Pressure Instrumentation
Since progressive cavity pumps are often used for pumping viscous
and solids-laden fluids, suitable isolation devices must be used with
the pressure measuring equipment to avoid plugging of the stem to
the pressure gauge or transducer. Suitable isolation devices have an
elastomeric or other pliable membrane in contact with the pumped
fluid. A reservoir behind the pliable member is filled with a suitable
sensing fluid and the pressure measuring device is threaded into a
port in direct contact with the fluid reservoir. Preferred devices will
not obstruct the fluid flow. If NPSH tests are to be performed, a compound gauge or transducer must be used on the suction of the pump
to permit both positive and negative pressures to be read.
601.3 Fluid Viscosity
The actual viscosity of a fluid as it passes through a progressive cavity
pump can have a significant effect on volumetric efficiency and
required shaft horsepower. Since most viscous fluids pumped by progressive cavity pumps are non-Newtonian, the actual fluid viscosity in
the pump and in the piping systems will depend on the shear rate.
Therefore, viscosity measurement instruments, which enable a plot of
viscosity vs. shear rate to be developed, are essential.
In reality, proper sizing and selection of a progressive cavity pump
requires some knowledge of fluid viscosity. Some pump manufacturers evaluate a potential customer's fluid and perform viscosity tests
prior to selling them a pump. If this data is available, then testing the
fluid viscosity in the field would serve to verify the rheological properties of the fluid, but would otherwise be of little value. If the viscosity
of the fluid was not evaluated prior to the test, then viscosity measurement instrumentation, which enables determination of the viscosity of the fluid at various shear rates, is essential.
If the pump is to be tested with water but will eventually pump a viscous fluid or slurry, the pump manufacturer should provide documentation supporting that any conclusions drawn from the water test
could be extrapolated to expected performance with the actual
process fluid.
601.4 Flow Measurement
Progressive cavity pumps are rated in terms of theoretical displacement per revolution. As the discharge pressure increases, the actual
output may be somewhat less than the theoretical displacement per
revolution times the shaft speed. This reduction in flow is due to
internal leakage, or "slip." Therefore, using the shaft speed and theo32
Positive Displacement Pumps
retical displacement to determine flow rate is not recommended at
discharge pressures in excess of 15% of the rated pressure limit of
the pump. A calibrated flow meter compatible with the process fluid,
or recording the time it takes to fill or empty a tank of known volume, are recommended for determining the flow rate at the specified
design point or across the range of operating pressures.
601.5 Input Power
Determining the pump input power for a progressive cavity pump in
the field is difficult. The power output of a three-phase AC motor
can be calculated from the formulas given in Section 400. However,
most progressive cavity pumps are not driven at synchronous motor
speeds, so speed reduction devices, such as gear reducers or belts and
pulleys, must be used to reduce the speed. Speed reduction device
specifications must be consulted to determine the efficiency of the
reduction device used in order to arrive at the pump-input power.
It is also common practice to use variable frequency drive (VFD)
packages for progressive cavity pumps. Many of the newer drives provide readouts of the power to the driven equipment. The drive manufacturer should be consulted for the accuracy of data obtained from
the readouts. O n a larger VFD it is possible to record the current and
voltage into the drive and obtain reasonably accurate power values
using the appropriate formulae. On smaller drives (approximately 10
HP and smaller), the accuracy of obtaining readings this way is questionable, and the drive manufacturer should be consulted.
602.0
Tests
The following tests are generally applicable to progressive cavity pumps as long as certain
characteristics of this type of pump are recognized. One is that the performance of progressive cavity pumps is affected by fluid temperature. Factory performance tests are typically performed with water at 20° C. Temperature changes affect both fluid viscosity and
pump clearances. As temperature increases, clearances and viscosity decrease and these
changes compete to determine the effect on slip, Therefore, if the pump is to be tested
with a fluid at a temperature or viscosity different than originally specified, the pump
manufacturer should be contacted for help in correlating the test results.
Progressive cavity pumps recommended for use when pumping fluids at temperatures in
excess of 70° C are typically assembled with undersized rotors. This is necessary to
accommodate the significant thermal expansion of the stator elastomer and prevent excessive compression between the rotor and stator. If the pump is to be tested with a fluid that
is not at the same temperature as the process fluid, performance may not meet the specified flow rate at the specified pressure. The pump manufacturer must be contacted to correlate recorded performance results to the specified operating conditions.
33
AlChE Equipment Testing Procedure
Progressive cavity pumps intended for highly viscous fluids, but tested on water or a similar low viscosity fluid, may produce performance test results that do not correspond to the
specified operating conditions. The pump manufacturer should be contacted for assistance
in correlating the test results to the specified process conditions.
602.1 Performance Tests
Performance tests can be carried out in accordance with the procedures described in 502.1.
602.2 NPSHTest
The minimum suction pressure test (NPSH) can generally be performed as described in paragraph 502.2. However, the unique characteristics of progressive cavity pumps permit them to be used in low
suction pressure applications where the flow rate is considerably
below the 5% reduction in flow defined by The Hydraulic Institute.
Therefore, the test described in paragraph 502.2 may be continued
until the onset of clearly audible noise from the pump, until the pressures become erratic, or until there is no flow from the pump,
whichever occurs first. In performing tests where a valve is slowly
closed to create a restriction in the suction and or discharge lines, it is
possible that the nearly closed valve will create cavitation across the
valve, and will often be quite audible. The noise originating from the
valve should not be confused with noise related to pump cavitation.
Whenever possible and affordable, pumps should be bench tested at
the factory to avoid NPSH problems during start-up. Correcting
NPSH problems after installation can be expensive and impractical.
603.0
Other Tests
603.1 Sound Pressure Level
For most applications and operating conditions the sound pressure
level of progressive cavity pumps is less than the driver sound pressure level. Therefore, determining background sound pressure levels
before operating the pump is extremely important for obtaining accurate readings. The procedures outlined in paragraph 503.1 are appropriate for use with progressive cavity pumps.
603.2 Vibration Measurements
Rotors in progressive cavity pumps rotate eccentrically within the stator.
This results in unbalanced forces, which are generally absorbed by the
rigid supports and mounting structures typically used with progressive cavity pumps. However, these forces can affect readings taken on the bearings, reducers, and other components. Therefore, if vibration readings are
to be used for predicting maintenance intervals, it is important to make
accurate baseline measurements before and during pump operation.
34
Positive Displacement Pumps
603.3 Temperature Measurements
Temperature measurements are generally of limited use in determining
appropriate maintenance intervals for progressive cavity pumps. However,
if temperature is to be used as a possible indicator of required maintenance, baseline readings should be taken after the pump has been in normal operation for a minimum of 100 hours. Certain components of PC
pumps, such as the bearings and universal joints, may operate at slightly
elevated temperatures until the lubrication is evenly distributed and the
components are seated.
603.4. Miscellaneous
As with all new or different equipment, the manufacturer should be contacted if there are any doubts or questions about its safe and proper operation. This is especially true of positive displacement pumps, since many are
capable of developing high pressures and require safety protection to
avoid equipment failure and possible injury to personnel.
35
AlChE Equipment Testing Procedure
700.0 Air-Operated Diaphragm Pumps
The objective of diaphragm pump testing is to measure the performance of a pump
under a known set of conditions. Pump performance may, in turn, be defined by a group
of inter-related variables, including liquid flow rate, the air inlet pressure, the liquid inlet
pressure, the liquid discharge pressure, and the kinematic viscosity of the fluid being
pumped. When conducting a test involving head pressure, the total dynamic head (TDH)
needs to be used. The T D H is the difference of the total discharge head and the total suction head. Typically, flow and air consumption are considered dependent variables, and
the others are considered independent variables. However, sometimes the flow is held constant and the resulting air inlet and T D H pressures are recorded. Note that these tests are
commonly used for factory testing, but field conditions may not be suitable for performing
these tests without modifications.
700.1
Recommended Installation
There are four factors that need to be addressed when installing an air-operated double
diaphragm pump. These factors are listed in the following sections.
700.2
Access
700.3
Air Supply
Convenient access to the test pump is very important. If there is adequate access to the
test pump, technicians will have an easier time performing tests and routine inspections.
Ease of access can play a key role in speeding up the testing process.
Every pump location should have an air line large enough to supply the volume of air necessary to achieve the desired pumping rate. Use air pressure up to 125 psi (8.6 bar)
depending on pumping requirements.
For best results, pumps should use a 5 micron air filter and an air pressure regulator. Using
an air filter before the pump will ensure that the majority of any pipeline contaminants
will be eliminated.
700.4
Elevation
Selecting a site that is within the pump's dynamic lift capability will ensure that loss of
prime troubles will be eliminated.
700.5
Flexible Connections
Due to the natural reciprocating nature of the pump, it is recommended that flexible connections be used at the inlet, discharge, and air inlet of the pump. Flexible connections
between the pump and rigid piping will help to reduce the vibration of the pump.
The best installation location will be a site involving the shortest and straightest hook-up of
suction and discharge piping. Unnecessary bends, elbows, and fittings should be avoided to
keep friction losses to a minimum. In addition, the piping should be configured so that it
does not put any additional stress on the pump connections. A typical set up of a test
pump is shown in Figure 20.
36
Positive Displacement Pumps
Air-operated diaphragm pumps can handle a wide variety of liquids. The manufacturer
should always be consulted about the chemical compatibility of the test pump components
and the instruments used in the test.
Figure 20. Typical installation of a test pump
701.0
Test Equipment
Each of the twelve variables should have an instrument to record quantities during the
test. Fixed variables should always be measured and recorded to ensure that unknown
influences are not introduced.
701.1 Inlet Air Pressure (psi, kPa)
Inlet air pressure is typically varied for different tests through the use
of a pressure regulator placed on the inlet air line of the pump.
Pressure gauges and transducers should be accurate to within + 5%,
and the test pressures should be within 20% and 8 0 % of the gauge
range.
701.2 Fluid Discharge Pressure (psi, kPa)
The discharge pressure can be controlled through the use of a valve
placed in the discharge piping of the pump. Pressure gauges and
transducers should be placed between the valve and the discharge of
37
AlChE Equipment Testing Procedure
the pump. Pressure gauges and transducers should be accurate to
within ± 5 % , and the test pressures should be within 20% and 80% of
the gauge range. Discharge pressure is usually recorded in psig
(gauge) units (psig =psia + 14.7).
701.3 Fluid Inlet Pressure (in Hg, kPa)
The liquid inlet pressure can be controlled through the use of a valve
placed in the inlet piping of the pump. Pressure gauges and transducers should be placed between the ball valves and the inlet of the
pump. Pressure gauges and transducers should be accurate to within
± 5%, and the test pressures should be within 20% and 80% of the
gauge range. Suction pressure is usually recorded in psia (absolute)
units.
701.4 Process Fluid Temperature (°F, °C)
Process fluid temperature should be measured and recorded several
times during the test. The thermometer or thermocouple should be
accurate to within + 5%, and the fluid pressure should be within
20% and 80% of the gauge range. Record the process fluid temperature on the Field Test Data Sheet in Table 8.
701.5 Environment and Inlet Air Temperature (°F, °C)
Environment and inlet air temperatures should be measured during
the test. The inlet air temperature reading should be taken as close to
the pump inlet as possible. This is typically done through the use of a
thermometer placed in the air line just before the pressure regulator.
The environment temperature readings should be taken in the same
area as the test pump location. The thermometers or thermocouples
should be accurate to within ± 5 % , and the air temperature should be
within 20% and 80% of the gauge range. Record environmental and
inlet air temperatures in the Field Test Data Sheet in Table 8.
701.6 Viscosity (SSU, centipoise)
The simplest way to determine the viscosity of a liquid is to measure
the liquid temperature, then find the viscosity from a temperature vs.
viscosity table for that liquid. These tables are available from the
manufacturer or in reference books. If no table is available, one may
be created using a viscometer to measure the liquid at various temperatures. The thermometer or thermocouple should be accurate to
within ± 5% and the air temperature should be within 20% and 80%
of the gauge range. Record the viscosity in the Test Data Sheet in
Table 8.
38
Positive Displacement Pumps
701.7 Specific Gravity
The simplest way to determine the specific gravity of a liquid is to
measure the liquid temperature, then find the specific gravity from a
temperature vs. specific gravity table for that liquid. These tables are
available from the manufacturer or in reference books. The thermometer or thermocouple should be accurate to within ± 5°/0, and
the air temperature should be within 20% and 80% of the gauge
range. Record the specific gravity in the Field Test Data Sheet in
Table 8.
701.8 Ambient and Inlet Air Relative Humidity (%)
The simplest way to measure the ambient relative humidity is to use a
relative humidity sensor or a sling psychrometer. If a sensor is not
available, then ambient relative humidity can be calculated by measuring the wet and dry bulb temperatures to determine the relative
humidity. The inlet air relative humidity reading should be taken as
close to the inlet of the compressor as possible, and the ambient relative humidity readings in the same area as the test pump location.
Record the ambient and inlet air relative humidity on the Test Data
Sheet in Table 8.
701.9 Air Consumption (SCFM)
The best way to measure the amount of air used by the pump is by
an air consumption meter. The meter should be placed in the air inlet
line between the compressor tank and the pump inlet. If a reading is
taken in ACFM (actual cubic feet per minute), then it should be converted to SCFM (standard cubic feet per minute). SCFM is the standard of measurement used by the American Society of Mechanical
Engineers and the Compressed Air & Gas Institute, and is the reading taken at 14.7 psia, 68° F, and 36% relative humidity. The meter
should be accurate to ± 5% and the measurement should be within
20% and 80% of the meter range.
701.10
Flow (GPM, m 3 /hr)
A flow meter installed in the discharge line of the pump is the simplest method for measuring flow. Alternatively, flow can be determined by measuring the amount of time it takes to fill a tank of
known volume. The flow meter should be installed downstream from
the pump with a minimum of 10 pipe diameters of straight pipe
between itself and any fittings or flow restrictions, such as a discharge
valve. The flow meter should be accurate within + 5 % , and the measurement should be within 20% and 80% of the meter range.
39
AlChE Equipment Testing Procedure
Table 8. Datasheet for field test of an air-operated diaphragm pump
701.11
Sound (dBA)
Sound measurements should be taken using a sound level meter with
an octave band filter. Both meter and filter must meet ANSI S1.41983, and IEC-651 Type 2 codes. The measurement should be within 20% and 80% of the meter range.
40
Positive Displacement Pumps
701.12 Blow-by (ft/m, m/s)
Blow-by measurements should be taken using an air velocity meter,
accurate to ± 5%, and the measurement should be within 20% and
80% of the meter range.
702.0
Tests
702.1 Performance Test
To test the general performance of the pump, the following tests should be
performed.
702.1.1 FLOW: The purpose of this test is to determine the
amount of liquid the test pump will deliver over a certain period
of time, data which is then used to create the flow curves for the
pump.
Required equipment: flow meter, pressure gauges at the air inlet and
the discharge of the pump, pressure regulator, intake and discharge valves, SCFM meter.
To conduct this test, the air inlet pressure should be set to 20 psig
and the discharge head should be set to 0 psig. The pump is then
run for 1 minute and the air use and the flow rate are recorded.
The discharge head pressure is increased using the discharge valve,
and the procedure is repeated for the various air inlet and discharge head pressures listed in Table 9.
The results for this test are recorded in the Flow Test Data Sheet
in Table 9.
702.1.2 START-UP PRESSURE: The purpose of this test is to
determine the amount of air pressure needed to initiate operation
of the pump in the test application.
Required equipment: pressure regulator, and a gauge on the air inlet
of the pump.
To conduct this test, first set the pressure regulator so there is no
air entering the pump. Next, adjust the regulator slowly to release
air to the pump and continue until the pump begins to operate.
This procedure should be repeated three times, and average pressure at which the pump begins to run should be recorded.
Start-up pressure is recorded in the test data sheet shown in Table 8.
41
AlChE Equipment Testing Procedure
Table 9. Flow test datasheet showing startup pressure
Flow Test
702.1.3 STALL PRESSURE: The purpose of this test is to determine the minimal amount of air pressure needed to keep a pump
running in the test application.
Required equipment: pressure regulator, and a gauge on the air inlet
of the pump.
42
Positive Displacement Pumps
Table 10. Test inspection log for life test
To conduct this test, the pressure is slowly reduced to a running
pump through the use of the pressure regulator until the pump no
longer operates. This procedure should be repeated three times,
and average pressure at which the pump stops running should be
recorded in the Field Test Datasheet in Table 8.
43
AlChE Equipment Testing Procedure
702.2 Life Test
A life test is used to gather information on product wear and/or performance.
Required equipment: no additional equipment are needed for this test.
To perform this test, the pump is operated under normal conditions
for the test location until a wear part (diaphragm, ball, etc.) fails, or
for a specified amount of time. The pump is visually inspected periodically and the results are recorded in Table 10.
703.0
Other Tests
The following are optional tests users may want to conduct, but are not required.
703.1 Blow-by
This test is performed to measure the amount of air that passes
through the air valve/center section and out the exhaust at 100-psig
air inlet pressure when the discharge valve is closed.
Required equipment: pressure regulator, gauge on the air inlet line of the
pump, discharge valve, air velocity meter.
To perform this test, operate the pump at 100-psig line inlet pressure
and close the discharge valve. Place an air velocity meter at the
exhaust and measure the velocity of the air passing by. Results are
recorded, then the process is repeated with the discharge valve
opened slightly to allow the pump to shift once. The results are
recorded in Table 8.
703.2 Dry Vacuum
The dry vacuum test is performed to determine the maximum dry
vacuum the pump will draw. For this test the pumping medium is air.
Required equipment: vacuum gauge installed between the inlet valve and
the liquid inlet of the pump.
To begin this test, disconnect the inlet of the pump from the pumping medium, operate the pump at 10-psi inlet air pressure, close the
ball valve on the inlet fixture, and record the vacuum reading in
Table 11. Open the ball valve slowly to let the pump return to normal cycle. A total of three vacuum readings should be taken at each
inlet air pressure setting, and should be adjusted in 10-psi inlet air
increments up to 100 psig.
The results are recorded in the Vacuum Test Datasheet in Table 11.
44
Positive Displacement Pumps
Table 11. Vacuum test datasheet
703.3
Wet Vacuum
This test is performed to determine the maximum wet vacuum the
pump can draw. For this test the pumping medium is the process
fluid.
Required equipment: a vacuum gauge installed between the inlet valve
and the liquid inlet of the pump.
To begin this test, operate the pump at 10-psi inlet air pressure and
close the ball valve on the inlet fixture. Record the vacuum reading in
Table 11. Open the ball valve slowly to let the pump return to normal cycle. A total of three vacuum readings should be taken at each
inlet air setting, and the inlet air should be adjusted in 10-psi inlet air
increments, up to 100 psig. Results are recorded in the Vacuum Test
Datasheet in Table 11.
45
AlChE Equipment Testing Procedure
703.4
Sound Test (100/0)
Sound tests conducted at 100-psig inlet and 0-psig head are used to
quickly evaluate a product's sound emissions in the "A' band.
Required equipment: pressure regulator, a gauge on the air inlet line of
the pump, and a sound level meter with an octave band filter.
Ideally, the test should be performed in an area free from extraneous
sound. All other equipment in the testing area must be off. The procedure for obtaining sound emissions is based on OSHA Noise
Exposure Standard 1975. Results are recorded in Table 12.
Table 12. Sound test datasheet
704.0
Field Test Process Example
An example of a pump test installation in a water transfer application is shown in Figure
21 on the next page. A flow meter was installed downstream from the discharge ball valve
so the flows did not have to be measured using a scale. Gauges were installed in the air
inlet, just before the suction manifold, and just after the discharge manifold. The estimated
ideal operating point was at an air inlet pressure around 70- and 30-psi discharge head.
The target flow rate was at least 20 GPM. Air consumption was measured with an air
consumption meter. Fluid viscosity was measured at an ambient temperature of 80° F
before the test, and was found to be 31.5 SSU's. The specific gravity of water is 1. Relative
humidity readings were taken using a sensor at both the inlets of the compressor, and in
the area of the test pump. The relative humidity of the test area and the inlet air were
65% and 70%, respectively. These readings were all recorded in Table 13.
46
Positive Displacement Pumps
Figure 21. Typical installation of a pump test system
704.1 Performance Test
Flow Test: For this test, the air inlet pressure was set to 40 psi and
the discharge valve was completely open. The T D H for this test was
calculated to be approximately 22 psi; therefore, no readings for the
flow test could be taken at head pressures lower than 30 psi. The
pump was first operated at 40-psi air inlet and 30-psi discharge.
Readings were taken from the flow and air meters and recorded in
Table 14. The process was repeated for all of the applicable inlet air
and discharge head pressures, and the results were plotted in Figure
22.
704.2 Observation:
The pump performed as expected. At normal operating pressures—
70-psi inlet air pressure and 30 psi discharge pressure—the pump had
a flow of 31.7 GPM, which is well above the required 20 GPM.
47
AlChE Equipment Testing Procedure
Table 13. Example of a field test datasheet for an air-operated
diaphragm pump in a water transfer application
These results are applicable for the liquid pumped during this test.
Using other liquids would change the viscosities and results would
need to be re-established through similar testing.
48
Positive Displacement Pumps
Table 14. Data from a sample flow test
AlChE Equipment Testing Procedure
Figure 22. Sample flow curve
Positive Displacement Pumps
800.0 RECIPROCATING POSITIVE DISPLACEMENT PUMP
(RPDP) TESTING
This section covers the testing of piston and plunger pumps, although many of the considerations are similar to diaphragm pumps operated by a reciprocating mechanism. In a pis ton pump, the seal moves with the piston. In a plunger pump, the plunger moves within a stationary seal. Although they are used for pressures as low as 100 psi, they are typically
known to operate at high pressures, from 300 psi to 15,000 psig.
The major advantage of modern piston, and especially plunger, pumps is that they are virtually slip-free, so that the flow is independent of pressure. Volumetric efficiency is reduced
at very high pressures due to compression of the metal surrounding the plunger (the
plunger cavity/cylinder increases in volume) or when liquid compressibility starts to
become significant. For practical purposes, compressibility up to 8,000 psig for liquids such
as water can be ignored. With more compressible liquids, such as liquid COo, compressibility comes into play much earlier.
Piston pumps are generally limited to operating at less than 1,500 psig because of the limited support offered to the seal.
800.1
Safety Precautions
When these pumps are tested, it is important to remember that they move discrete volumes of liquid. These volumes are defined by the displacement of the piston or plunger,
are cut off from the inlet feed when the inlet valve closes, and are discharged when the
cylinder pressure exceeds the pressure on the discharge side. There is no going back! So,
be careful not to dead-end the pump during test. The liquid has to go somewhere or
something else has to give. Therefore, it is essential to first ensure that there is a safety
valve fitted on the discharge side of the pump. Any system changes necessary for the tests
must be installed after the safety valve.
800.2
Piping
There are two phenomena with RPDPs that affect the piping, and these should be given
consideration over and above the general piping requirements provided in Appendix C,
paragraph 900.3.
There is torque about an axis perpendicular to the crankshaft, and at its center. As one
side plunger is under pressure, it is pushing back on the crankshaft, trying to twist it. As
the crankshaft rotates and the opposite side plunger comes under load, it tries to twist the
crankshaft the other way. For a horizontal pump, this creates a side-to-side rocking movement at the pump head of very small magnitude. However, if there is a long, rigid pipe
attached to the head, what might be a very small movement at the head can become very
large at the other end of the pipe. It is therefore very good practice to install flexible links
51
AlChE Equipment Testing Procedure
in both inlet and discharge lines, close to the pump. As discharge pressures are usually
high, high-pressure hose can be relatively stiff, especially under pressure. If space is tight,
use a loop of hose to isolate the movement.
As individual cylinders operate, there is a discrete forcing frequency to the flow. If there is
a resonant length of pipe in the system, this can lead to noise and/or damage to the piping, especially on the discharge side. On the inlet side, design care should be taken to
review the requirement to accelerate the liquid into the cylinders as well as the bubble
point of the fluid being handled. The supplier should be consulted for proper design considerations.
800.3
Test Objective
The objective of the test is to measure pump performance at the operating point or over
its range of operating points. The principal values that need to be measured are flow
through the pump (Q), pump shaft speed (rpm), pressure at the discharge port (p^), and
pressure at the inlet port (ps). Pressures can vary with time: maximum discharge pressure,
as well as its average, should be recorded. A whole duty cycle should be examined as the
actuation of system valves can cause pressure spikes. For the inlet pressure, both maximum
and minimum are required in order to establish how well the pump is running, preferably
as a pressure trace versus time that would allow subsequent frequency analysis.
The viscosity and density of the liquid have less influence on the power absorbed by the
pump than with other designs. Providing a full charge of liquid can enter the cylinder on
demand (i.e., sufficient NPSHA), viscosity has little effect on flow.
Unless these pumps run very slow (less than 100 rpm) and at low discharge pressures (less
than 300 psi), the pumps have a very high efficiency (over 80%). Therefore, it is only necessary to check that the motor draws no more than its rated current at the rated voltage.
Voltage and current values can be used to calculate the power absorbed if it is required.
Table 15. Data collection table for reciprocating pump test
Data Collection
Date:
Site:
Liquid:
Max liquid Temp
F/C:
Speed
RPM
Flow Average discharge
US gpm Pressure-psi(g)
T e s t e d by:
Vp @ Max Temp:
Specific
Gravity:
Psl(a)
Viscosity:
centipoise (cP)
Maximum discharge Maximum inlet
Pressure - psi (g)
Pressure- psi (a)
52
Minimum inlet Drawn
Pressure" - psi(a)HP:
Positive Displacement Pumps
801.0 Test Equipment
Any instruments to be used in testing should have been recently calibrated. Instrument
accuracy is often quoted as a percentage of full-scale reading. A 2000-psi gauge with a ±
2% accuracy will measure to ± 40 psi. That is a ± 4 % accuracy for a measurement of
1000 psi. The same accuracy on a 5000-psi gauge is ± 100 psi to give ± 10% accuracy at
1000 psi. Gauges used should be properly sized for tested range.
801.1 Shaft Speed
Shaft speed should be measured by a tachometer, as with other PD
pumps. If it is acceptable that the flow rate can be ± 5%, then the
tachometer needs to measure to + 2 % at the test speeds. Use of calibration charts is recommended. The measured value should be
recorded, the correction from the chart logged, and the corrected figure calculated. This is best achieved when the tachometer has a digital readout. The column for shaft speed data in Table 1 could be
expanded to add:
Measured
rpm
Correction
Arpm
True
rpm
801.2 Suction Pressure
It is important to keep the liquid well away from forming vapor. This
is why absolute gauges are preferred (psia) to avoid dealing with negative numbers. Generally, the minimum pressure required, or the
NPIPR, is sufficiently large that the normal sea level variations in
atmospheric pressure can be neglected. At higher altitude it may be
necessary to record the barometric pressure and increase the NPIP
accordingly. Ninety percent of problems with RPDPs are associated
with poor inlet conditions. Do not compromise when testing inlet
pressure.
The most effective way to measure inlet pressure is with a pressure
transducer. Pressure variation generated by a smooth-running pump
will mean that pressure gauges need to be glycerin-dampened to prevent them from being damaged. This dampening hides the fluctuation. At the frequency of the variations, an undamped gauge cannot
respond fast enough. When there is a problem, the variations can be
extremely violent.
A pressure transducer requires circuitry to provide a stable input voltage and to display the output voltage. The choice of transducer and
53
AlChE Equipment Testing Procedure
display must take into account the response rate needed to catch the
transients. A value less than 20 kHz is unlikely to be useful.
Inexpensive instruments that display mean and peak values of pressure are available. Output can always be ported to an oscilloscope to
display the waveform.
When instruments are calibrated, ensure that a square wave input signal produces an almost square wave output. It should not overshoot
or undershoot. Know what the pressure is doing, not what the electronics are doing wrong!
It is not always possible to fit transducers in ideal positions. However,
aiming for the ideal will give more reliable results. Install the transducers with the "pocket" upwards. Fill with liquid when possible to
reduce any possibility of dampening from air pockets. Do not fit to
the outside or inside of bends. Fit the transducer as flush to the inside
of the pipe as possible.
If the pump is being run under conditions of severe cavitation, the
transducer can be damaged when exposed for too long. If this is suspected then isolate the transducer with a valve to limit its exposure (at
the expense of accuracy). Solve the problem of the cavitation before
refitting the transducer correctly.
801.3 Discharge Pressure
A glycerin-damped calibrated pressure gauge is often sufficient for
measuring discharge pressure. (Note: the site gauge may not be reading cor redly!). However, if vibrations are a problem (pipe noise, fatigued
welds, etc.) then the pressure transducer helps aid the analysis. The
discharge pressure usually varies considerably because of varying
restrictions to the flow. Absolute accuracy is not usually demanded, so
use a transducer with a high maximum pressure to avoid damage
from pressure spikes.
801.4 Differential Pressure
RPDP produces flow of liquid, which is, ignoring compressibility
effects, independent of the input pressure. The discharge pressure is
solely determined by the downstream restrictions. High inlet pressure
will, however, reduce the power absorbed. Inlet pressures in typical
installations are usually not high enough to be taken into account
when determining the power requirement. Ensure that the maximum
inlet pressure specified by the manufacturer is not exceeded.
801.5 Crankcase Temperature
Crankcase temperature is not usually a consideration unless conditions are excessive (over 140° F), in which case it is necessary to
54
Positive Displacement Pumps
ensure that the oil is capable of performing at this temperature, and
the supplier has to be consulted.
801.6 Liquid Temperature
Most methods for determining temperature are adequate. Ambient
usually covers most applications. However, where cavitation is suspected, it is necessary to check the inlet pressure trace at the maximum possible liquid temperature. Feeding the discharge to a back
pressure regulator and returning the bypass to the supply tank will
often be sufficient to raise the feed temperature to the necessary
value.
801.7 Vapor Pressure
Vapor pressure is the most critical liquid characteristic for RPDPs. A
margin in excess of vapor pressure is required at the inlet at all times,
and will depend upon pump design (valve spring stiffness, etc.). The
pressure in the liquid will be lowered as it is accelerated through the
valve opening. The required margin will also depend on the liquid's
characteristics as it approaches its vapor pressure. An example is the
liquid's specific heat, which affects the vaporization temperature and
rate.
801.8 Viscosity
Pump flow is virtually independent of liquid viscosity until the viscosity reaches a value where the cylinder does not become filled quickly
enough. This is dependent upon the rpm. For viscous liquids, the
pump should run slower and increased NPIP may be required.
Absolute accuracy for determining the viscosity is not needed. When
checking, ensure that the lowest running temperature is used to determine the value. Then consult the pump manufacturer as to the maximum recommended rpm and NPIP for that viscosity. Very low viscosity applications are not usually recommended for positive displacement pumps.
801.9 Flow Rate
Flow rate is the most important parameter to measure. A calibrated
flow meter can be used, although these meters are expensive for the
pressure ranges of these pumps. Using a back pressure regulator, and
having the flow meter on the bypass line, allows a low-pressure flow
meter to be used for testing. Ensure that there are no other valves or
paths flow can pass through when fitting such a regulator. Do not isolate the safety valve, which must have an open exit port from which to
check that it is not passing liquid. If it is practical, diverting the back
pressure regulator bypass flow into a container for a timed duration is
the most accurate method. The flow can fill a container to a prede-
55
AlChE Equipment Testing Procedure
termined volume or it can be weighed before and after, and the mass
adjusted by the specific gravity to get the volume.
When these methods are impractical, or a number of pumps are running in identical installations and need to be tested, a calibrated orifice is another solution. The pressure generated to force the flow
through the orifice is recorded, and then checked against the orifice
calibration to determine the flow rate.
801.10 Input Power
For an electric drive it is possible to measure the input voltages and
currents and use the formulae given in paragraph 400.3. If there is a
gearbox or pulley drive causing a speed reduction, then this can
absorb up to 5% of the input power. If there is a high power absorption by the speed reducer, then there will be evidence of abnormal
heat generation. For sheave drives it is necessary to check for belt slip.
Belt slip will cause heat buildup and premature belt failure.
802.0
Standardized Tests
802.1 Performance Test
The purpose of this test is to check to see if the pump is performing
according to specification. Usually it is only possible to test at the
installed speed. However, when a variable speed drive is used, the
tests can be repeated a number of times at different speeds and the
results plotted. For multiple speed tests it is suggested that each set of
results be separated by at least two empty lines when using Table 16.
Before testing, obtain site information about causes for concern, such
as loss of pressure, vibrations, etc. Set up the pump with the necessary instruments and piping gauges. In addition to installing the pressure transducer, the inlet piping should not be altered, as this will give
a false test. If a back pressure regulator is installed, back off the
adjustment. SLOWLY adjust the regulator until the desired pressure
is reached. In the event that a complete turn of the adjustment does
not give an increase in pressure, then back off one turn and adjust no
further.
Run the pump to purge the system of air for about 20 minutes.
Then, take the required measurements as close to each other in time
as is practical. Log the results.
After testing, the manufacturer's data can be entered in a different
color pen on the line under the test results in Table 16. The next line
can be used to highlight differences that need attention.
56
Positive Displacement Pumps
802.2 Inlet Pressure Trace
A pressure transducer should be fitted just upstream of any smoothing device. It should ideally be installed facing up with the pocket
filled with liquid. This will avoid an air pocket that might dampen
any signal. Connecting the transducer to a balanced Whetstone
bridge circuit will give an output that can be viewed on an oscilloscope. A trace can be printed and compared with the maximum and
minimum values provided by the manufacturer.
803.0 Other Tests
803.1 Sound Pressure Level
A sound pressure level test can be carried out as per paragraph
500.3.1.
803.2 Analysis of Results
Did the pump produce the correct flow against the back-pressure
regulator?
If "YES" — Inlet pressures acceptable?
If "YES" — The pump is OK. Worn restrictions or other system
problems may cause operational low pressure or vibrations. See
paragraph 800.0 for more help.
If " N O " — Improve the inlet conditions and re-test. See section
paragraph 800.0 for explanation.
If " N O " — Is the inlet pressure acceptable?
If "YES" — Check the pump seals or packing rings, orings and all mating faces. Replace worn parts and re-test.
If this has been done and the results still require a re-test,
seek help from the manufacturer.
If " N O " — Improve the inlet conditions and re-test.
804.0
Test Process Example
The instrumentation included a tachometer, a weighing scale, a pressure gauge, and a
digital oscilloscope. All the instrumentation had been currently calibrated, and was accurate so that no correction needed to be made. Operators used the calibration table (Table
17), which records the instrumentation used. The inlet pressure trace is also shown in
Table 18.
57
AlChE Equipment Testing Procedure
Figure 23. Horizontal triplex pump,
Duty 12.5 US gpm, at 1275 psig for pumping methanol; tested using water.
Table 16. Test results
Maximum experimental error
(48.55 - 48.40) MOO / 48.55 = 0.3% Accepted
58
Positive Displacement Pumps
Table 17. Calibration table
AlChE Equipment Testing Procedure
Table 18. Inlet pressure trace
Positive Displacement Pumps
900.0 Auxiliaries
900.1
Appendix A: Seals
Sealing arrangements for positive displacement pumps are similar to other types of rotating equipment, such as centrifugal pumps. Positive displacement pumps may be sealed
with packing or a mechanical seal, depending on the service conditions. The stuffing box
or seal chamber is normally located on the suction side of the pump. The seal will then be
subject to pump suction pressure. If the pump is run in reverse direction, the seal will be
subject to discharge pressure. An example of a seal subject to reverse pressure can be
found in applications involving high-suction lifts on progressing cavity pumps. Here reverse
pressure operation, for a short period of time, occurs when the suction pipe is filled. If the
suction line contains restrictions, such as a foot valve or similar device, the exit pressure
from the pump to the seals can be excessive, which can result in damage to the sealing system. Some positive displacement pumps, such as screw pumps cannot, by design, run in
the reverse direction.
900.1.1 Packing
When packing is used to seal the equipment, care must be taken to
ensure that the installation is done correctly. If the installation is the
replacement of existing packing, be sure the sealing surfaces on a
shaft or sleeve are not scored. Consult the manufacturer's recommended procedures for the installation of specific grades or types of
packing. Note that the ends of the packing rings, when assembled to
the equipment, must be off-set by 90° from each other for maximum
leakage control.
Basic causes for packing malfunction and tests for corrective action
are:
900.1.1.1 Stuffing box overheats—Here the packing has been installed
too tight. Release the gland pressure and retighten. Be sure leakage is present at the packing.
900.1.1.2 Pump leaks excessively—In this case, the packing may be
too loose. Tighten the packing. If heavy leakage still continues,
check for shaft or sleeve damage. Repair or replace as required.
900.1.1.3 Not enough liquid being delivered by the pump—In this case,
suction pressure may be less than atmospheric pressure. Determine
if air is leaking into the stuffing box when the pump is running.
The corrective measure is to retighten the packing.
61
AlChE Equipment Testing Procedure
900.1.2
Mechanical Seals
Many positive displacement pumps use mechanical seals. Once an
installation is made, no further adjustments are required. However,
liquid circulation to the seal chamber is required to remove the heat
developed at the seal faces.
Reliability of the entire pump and seal assembly is important and
may be confirmed through dynamic and static testing.
900.1.2.1 Dynamic testing—Some applications will require a
dynamic test before the unit is shipped from the pump manufacturer. Here water or oil would be used in a performance test and a
visual check needs to be made of any leakage coming from the
seal area. The acceptance criteria may vary depending on the
application. Normally up to three drops of water per minute or a
slight moistening of the exterior surface of the seal chamber with
oil is acceptable after the pump has run briefly.
900.1.2.2 Static testing-Where practical and possible, the pump
containing the seal can be pressurized with a test fluid, such as oil
or air, and then blocked off. The pressure decay over a short period of time is then monitored. Air pressure tests are easier to perform. Air at 10 psig can be used for testing, and units are considered acceptable when the pressure decay is less than 2 psi over a
period of 30 seconds.
900.1.2.3 Dual seal testing-Some applications involving fluids that
are hazardous to the environment and present a safety issue to a
chemical process plant or refinery may require a dual seal installation in either a double or tandem seal arrangement. Double seals
may be tested statically in the pump using any pressure decay over
a given period of time. Similarly, a tandem seal may be pressure
tested statically as well. In this case, the pump and the inboard seal
are pressurized to operating pressure. Leakage through the
inboard seal of the tandem seal arrangement will be detected by a
change of pressure in the outboard seal cavity. This is accomplished by blocking off the outboard seal cavity at atmospheric
pressure for 10 minutes and noting the increase in pressure.
Advances in seal technology and construction materials have
allowed positive displacement pumps to be applied to more
demanding applications such as hot chemicals and viscous fluids.
As heat generated between the seal faces can become significant,
manufacturers' recommendations for installation and cooling need
to be implemented to avoid premature failure.
62
Positive Displacement Pumps
900.2
Appendix B: Bearings and Rotor Dynamics
The vibration of positive displacement pumps is typically not an issue in regard to expected performance. However, the design of the majority of these pumps can give rise to very
large hydraulic forces. As a result of this fact, the pump components must be designed to
avoid natural frequencies that could be excited by the system hydraulics. The rotor-bearing system should be designed so there is essentially rigid shaft performance over the
expected operating speed range. This includes the excitation from the once per rev component but, more importantly, the multiple from the number of cylinders or chambers or
vanes or gear teeth that produce the hydraulic force frequency to the casing vibration.
No pump rotor or stator component should have a damped critical speed that is below
130% of the highest fundamental hydraulic force frequency. Calculations can account for
hydraulic stiffness and damping of the pump element and the rotor sealing system.
It is desirable to mount these pumps on rigid and or massive foundations that result in a
casing rms. vibration level of less than 1 in/sec. Documented successful operation at higher vibration levels should also be available to users in order to justify these designs. The
stiffness of the mounting structure to satisfy the above vibration levels can be predicted or
verified by test data from the pump in place. A massive foundation, with a mass to
hydraulic force ratio of 4 or more, is suggested to better assure that vibration levels are
acceptable.
Internal (product-lubricated) sleeve journal bearings are often used in many rotary pump
designs. The lubrication of these product-lubricating bearings is critical to successful operation. If viscosity of the pumped fluid is sufficiently high, hydrodynamic lubrication
occurs. In this case, the rotor does not contact the sleeve and so the composition of the
bearing material is not important. However, if the viscosity of the pumped fluid is low, the
fluid film supporting the rotor becomes thin or disappears, causing the rotor to contact the
sleeve. The composition of the bearing material becomes very important in such cases.
Typically, rotary pump product-lubricating bearings are made of bronze, iron, carbon, silicon carbide, or sometimes of plastics. A "dry running" (low-viscosity) lubrication of these
bearings is characterized by the so called PV value, where P = bearing projected unit loading in psi, and V = journal velocity, ft/min. The approximate upper limits for these materials are listed below.
Table 19: Materials data for pump internals
63
AlChE Equipment Testing Procedure
The selection of the material for the pump internals is also important. For example, gear
pumps used for chemicals need to have a variety of material internals, such as stainless
drive gear running against Teflon idler gear, or analogous dissimilar material combinations. Running similar material combinations, such as stainless steel against stainless steel,
should not be used for gear pumps for chemicals, as galling can occur, and the life of a
pump would be significantly reduced.
900.3
Appendix C: Piping
900.3.1 Piping-size considerations
900.3.1.1 Suction-a compromise between reducing the cost by
using smaller pipe size, and providing sufficient suction pressure, in
terms of NPSHA at the pump inlet by using larger pipe size. The
smaller the pipe size, the higher the friction, and, consequently, the
greater the NPHA losses.
Historically, and as a rule of thumb, the suction pipe is normally
set for flow velocities of 5 ft/sec or less.
900.3.2 Discharge piping
Trying to minimize the installation cost by abruptly changing the size
of the discharge pipe can create many problems. The turbulence created by an abrupt change in the discharge piping, known as the vena
contracta effect, can significantly affect the performance of the pump.
Because discharge piping typically is significantly longer then suction
piping, and thereby has a more significant impact on cost, the rule of
thumb and a primary approximation is to keep the velocity in the
pump discharge pipe under 15 ft/sec.
900.3.3 Bringing an appropriately supported pipe to the pump.
It should be realized that piping issues directly affect the pump's life
and its performance. Bringing the pump to the pipe in one operation
and expecting a good pump flange or vessel fit is a very difficult, if
not impossible, task. When bringing the pipe to the pump, the last
spool should always be left until the pump has been leveled in place
and roughly aligned. At this point, the pipe should be securely
anchored just before the last spool to prevent future movement
toward the pump's flanges. Fig. 24 shows typical anchors at the pump
suction.
64
Positive Displacement Pumps
Figure 24. Typical anchors for the pump piping
Piping lay out should not be finalized until certified elevation drawings are received from the engineering group or from the pump vendor. Once the final certified prints are received, the final isometrics
and the piping takeoff can be completed.
900.4 Appendix D: Installation
Equipment can be delivered to a site either early or late. When the equipment is late, it is
critical to have certified elevation prints of the equipment available when it arrives. The
certified prints of the isometrics required for the piping takeoffs can be made without
impacting the construction schedule. If the equipment is early, it will arrive at the site
prior to the construction team's readiness. In such cases, early preparations must be made
for long-term storage. It is customary to use oil mist lubrication to keep the equipment in
as-shipped conditions during storage. Pressurization of the bearing housing and the casing
with 10 to 20 psig H ^ O pressure prevents moisture and contaminants from entering the
sealed areas and damaging the components. Early delivery of equipment to the site has
the advantage of allowing for verification of actual measurements.
Once the location of the equipment is set, the baseplate can be put in place, leveled and
rough-aligned, and the equipment mounted. Rough alignment of the equipment should
be done prior to building the grout forms, as illustrated in Figure 25.
65
AlChE Equipment Testing Procedure
Figure 25. Rough alignment phase.
Note that the motor and the pump are not coupled yet, and the baseplate is still sitting free, not grouted.
900.4.1
Grouting
Once you are satisfied with the rough alignment, remove all the
equipment (pump, motor gearbox, etc.) from the baseplate. Level the
baseplate to a maximum out of level of 0.025" (0.06 mm) from end
to end in two planes. Use machined pads as the base for the leveling
instruments. Inspect the foundation for cleanliness, and, if not clean,
use solvent to remove grease and oil. (See Figure 26).
66
Positive Displacement Pumps
Figure 26. Baseplate leveling pads and grout location
Allow time for the cleaning substances to evaporate. Form the base
using the appropriate techniques to allow for the weight, temperature
rise, and fluidity of the grout material. Grout the base using epoxy
grout. Allow the grout to cure, following the grout manufacturer's
recommendations. This normally requires 24 hours at 80 °F (27 °C).
Remove the forms and clean all sharp residue and edges from the
foundation. Figure 27 shows details of a typical baseplate, with
anchor bolts and grouting.
Figure 27. Typical anchor bolt and leveling wedges
67
AlChE Equipment Testing Procedure
The rough alignment step mentioned earlier is critical to minimize
the changes that will be required to appropriately fit the piping to the
pump. At the last stage, when the final spools are installed, the final
alignment will be achieved with small adjustments. This will minimize
the adjustments required on the motor feet/bolts. Unfortunately,
motor hold-down bolts are often too tight and allow only for small
adjustments to the motor before becoming bolt bound. Motor manufacturers could improve this situation significantly if motor feet were
designed to be slotted, rather than drilled, for bolts. Figure 28 shows
the tightness of space available to insert the foot hold-down bolt.
Figure 28. Potential bolt-bound situation due to tight clearances
between bolt, feet, and base
This illustrates once again why good alignment at step 3 can save
time and the cost of having to alter motor feet (a nightmare) by slotting or reaming.
900.4.2 Re-installation of the equipment and final alignment
Reinstall the pump and the motor on the baseplate. Rough-align the
equipment again, using reverse indicator or laser alignment or similar
accurate techniques, as shown in Figure 29.
68
Positive Displacement Pumps
Figure 29. Rough alignment after grouting
It should now be easy to fine-tune motor movement within the allowable alignment range without it becoming bolt bound. This is possible
because of the rough alignment during the prior step (step 4).
Note: Never install shims under the pump feet. If the shims are lost or mis placed, then alteration to the piping may be required to bring the pump to within
the required alignment specification. The normal procedure is to place 0.125"
(3.2 mm) thick shims under the motorfeet. This allows for the adjustments that
will be required duringfinalalignment of the equipment.
Figure 30. Final connection of the suction piping
69
AlChE Equipment Testing Procedure
900.4.3 Final piping installation
Make up the final spool pieces for the suction and discharge spaces.
Bring the piping to the pump as shown below.
Figure 31. Final piping
900.4.4 Final alignment
Bring the piping to the equipment, take final measurements, and tack
weld the spools in place. At this time the spools can be removed and
taken back to the hot work permit area to finalize the weld. Leave a
square and parallel gap between the flange faces. The gap should be
wide enough to accommodate the size of the gasket required, plus
1/16 to 1/8", depending on piping sizing. (This is the only distance
over which the piping will be pulled. However, because the piping is
properly anchored before the spool pieces, this length is short, and
stresses are minimized). Finally, align the equipment, taking into
account hot and cold operating conditions, using two indicators on
the pump shaft coupling area (Figure 32).
70
Positive Displacement Pumps
Figure 32. Overhead view of the motor and pump
As the piping is tightened into place, the shaft must not be moved
more than 0.002" (0.005 mm); modify the spool pieces until the piping misalignment is fixed.
900.4.5
Suggested periodic maintenance
Several clues are common to piping misalignment. These clues
become apparent when mechanical seals and/or bearings run hot,
and parts fail. A quick analysis of the failed parts can clearly show
evidence of piping misalignment. To make a final confirmation of
the symptoms, unbolt the piping while measuring the movement in
the vertical and horizontal plane. Again, piping that moves more than
0.002" (0.005 mm) must be modified to correct the misalignment. See
Figure 33 for placement of the indicators.
71
AlChE Equipment Testing Procedure
Figure 33. Piping alignment verification
Place an indicator in the horizontal and vertical planes, using the
motor and pump coupling. Uncouple the pump and motor, while
watching the indicator movement. Start unbolting the flanges, and
continue watching for movement in the indicators. If the needle
jumps over 0.002" (0.005 mm), the piping must be modified to
improve the pump's performance.
72
Positive Displacement Pumps
1000.0 References and Bibliography
1. Rotary Pump Standards, The Hydraulic Institute, Publication A N S I / H I 3.1-3.5, 3.6.,
4.1-4.6, Parsippany, NJ, 2000.
2. API 610 Standard for Centrifugal Pumps, Revision 4 (ISO 13709), American Petroleum
Institute, Washington, DC, October, 2004.
3. API 676 Standardfor Rotary Pumps, Revision 4, American Petroleum Institute,
Washington, DC, March, 2000.
4. Centrifugal Pumps (Newtonian Liquids), 3rd Edition: A Guide to Performance Evaluation,
Equipment Testing Procedure, AlChE, New York, June 2002.
5. Rotary Positive Displacement Pumps (Newtonian Liquids), 2nd edition, Equipment Testing
Procedure, AlChE, New York, 1968.
6. Stepanoff, A.J., Centrifugal and Axial Flow Pumps, 2nd Edition, John Wiley & Sons,
1957.
7. Cameron Hydraulic Databook, 19th Edition, Flowserve Corporation, 5215 N. O'Connor
Blvd., Suite 2300, Irving, T X 75039; www.flowserve.com.
8. Nelik, L., Centrifugal and Rotary Pumps: Fundamentals with Applications, CRC Press, Boca
Raton, FL, 1999.
9. Rizo, L. and L. Nelik, "Piping-to-Pump Alignment," Pumps & Systems, April 1999.
73
AlChE Equipment Testing Procedure
INDEX
Ambient Relative Humidity
Anchor Bolts
Baseplate
Bearings
Belt Slip
Blow-by Test
Bolts
Break Horsepower
Cavitation
Compressibility
39
66
Glycerin Damping
Grouting
53,54
64,66,68
3, 64-67
8, 23, 30, 35, 62,63,70
56
41,44
66,67
4, 5, 14-16,26
Head
Positive Suction
Pressure
Pump Inlet
Total Dynamic
Velocity
3,4,36,41,46-47,51
3
36,41,47
3
4,36,41,47
4
3, 4, 30, 34, 54, 55
51,54
Inlet Port
4,52
Inlet Pressure. . 34,38,41,44,46,47,52,53-55,57
Damping
53,62
Diaphragm Pumps
11,37
Differential Pressure
3,4,6,13,18,19,24,54
Discharge
3, 4,8,10,12,21,53
Flange
3
Manifold
46
Port
14, 52
Pressure
6, 14, 19, 54
Valves
25
Dual Seal Testing
61
Dynamic Lift Capability .
36
Dynamic Viscosity
5,6
Elastomeric Material
Kinematic Viscosity
5,6,16,36
Lobe Pumps
Lubrication
9,16
35,63,65
Materials of Construction
Maximum
Differential Pressure
Discharge Pressure
Operating Pressure
Measurement
Flow
Temperature
Vibration
Pressure
Mechanical Efficiency
Minimum Required Suction
Pressure Test
Multiple-Screw Pumps
11,31-33
Flanges
3,13,24,63,71
Fluid Flow
32
Fluid Viscosity
13,17,24,32,33,46
Fluids
1,2,8,11,13,32-34,61
Flow, Net
3,5,13
Unit
13
Flow Measurement
13,32
Flow Meters
1,13,18,23,33,39,41,46,55
Flow Rate
18,33,34,36 41,46,53,55,56
8,11,62,63
24
24,52
27
13, 32
22.23,35
22,23,34
23, 32,52
56
29, 34
7,9,10,11,16,61
Net Flow
3-5,3
Net Positive Inlet Pressure
3,4,53,55
Net Positive Suction Head . . . 3,5,32,34,52,64
Newtonian Liquid
1,18
Non-Newtonian Liquid
1,17,18,32
Gauges . . . 1,13,17,24,36,37,38, 41,46,53,56
Gear Pumps
1,8,9,63
Packing
Performance Curves
74
57,61
20
Positive Displacement Pumps
Performance Tests
22,23,33,34
Piping . . 1,3,21,32,36-38,51,52,56,64,65,69,72
Piston/Plunger Pumps
7,12,51
Power
Fluid
4,5,15
Hydraulic
4,5
Pressure
Air
36,37,41,42,44-47,62
Capability
31
Differential
3,4,6,13,18,19,24,54
Head
36,41,47
Fluid Discharge
37,38,54
Inlet
38,41,53-55,57
Minimum Required
29,30,53
Regulator
55,56
Sound
34,57
Suction 3,5,6,13,18,20-22,29,30,34,38,53,
61,64
Vapor
34,57
Pressure Spikes
52,54
Pressure Trace
52,60
Progressive Cavity Pumps . . . 7,10,11,15,31-35
Pump Types
Diaphragm
11,37
Gear
1,8,9,63
Lobe
9,16
Multiple-Screw
7,9,10,11,16,61
Piston/Plunger
7,12,51
Progressive Cavity
7,10,11,15,31-35
Reciprocating Positive
Displacement
7,12,51-60
Rotary
1,16-30,63
Vane
10,16
Rotor-Bearing System
RPDP Piping Problems
63
51,52
Seals
23,57,61,62,71
Double
62
Mechanical
61,71
Pump
57
Shaft
23
Shaft Speed
1,16-18,24,31,32,52,53
Sling Psychrometer
39
Slip
3-5,13,15,32,33,51,56
Sound Pressure Levels
22,23,34,57
Start-up Pressure
41,42
Stall Pressure
42
Stator
11,31,33,34,63
Strobe Tachometer
13,17,24,33
Stuffing Box
61
Suction
3,5,11,12,16,21,24,30,36,61
Suction Manifold
46
Suction Piping
36,61,64,69
Suction Ports
5,16
Suction Pressure
3,5,6,17,18,20,21,29,30,
.
34,38,53,61,64
Actual Available
3
Maximum Required
29
Minimum Required
22,29,34
Suction Valves
21,25,29
Synchronous Motor Speed
33
Test Procedures
Tests
Blow-by
Dual Seal
Dynamic
Life
Performance
Static
Suction Pressure
Throttling Valves
Torque
Total Dynamic Head
Radial Hydraulic Force
8,10
Reciprocating Positive Displacement
Pumps (RPDP)
7,12,51-60
Resisting Load
5
Reverse Pressure
61
Rotary Pumps
16-30,63
Rotor
9-11,31,33,63
75
1,24,30
41,44
62
62
42,43
18,24,33,34,56
62
29,34
21
1,5,6,18,51
4,36,41,47
AlChE Equipment Testing Procedure
Unit Flow
13
Vacuum
Valves
Suction
Throttling
Vane Pumps
Variable Frequency Drive
33
Viscosity
4-6,8,11,13,16-18,21,
24,26,30,32-33,38,46,52,55,63
Dynamic
5,6
Kinematic
5,6,16,36
Volumetric Efficiency
4,6,27,32,51
3,44,45
21,25,29,38,41,52,55
21,25,29
21
10,16
Other Equipment Testing Procedure Titles
Centrifugal Pumps (Newtonian Liquids), Third Edition: A Guide to
Performance Evaluation
Continuous Direct-Heat Rotary Dryers: A Guide to
Performance Evaluation, Third Edition
Fired Heaters
Mixing Equipment (Impeller Type), Third Edition
Particle Size Classifiers, Second Edition
Spray Dryers
Tray Distillation Columns, Second Edition
For information on these and other titles,
check AlChE's online catalog at
http://www.aiche.org/pubcat
76