A practical guide to compressor technology 2nd ed heinz p bloch (wiley, 2006)

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A PRACTICAL GUIDE TO
COMPRESSOR TECHNOLOGY


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ABOUT THE AUTHOR

Heinz P. Bloch is an internationally respected authority in all areas of machinery operations, troubleshooting, and repair. He was with the Exxon Corporation for over 20 years,
and is now the principal of Process Machinery Co. Mr. Bloch is also the author or coauthor of
15 other books, including Improving Machinery Reliability, Machinery Failure Analysis,
Machinery Component Maintenance and Repair, Major Process Equipment Maintenance, and
Compressors and Applications, as well as more than 330 articles or technical papers.


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A PRACTICAL GUIDE TO
COMPRESSOR TECHNOLOGY
Second Edition

HEINZ P. BLOCH
Process Machinery Consulting
West Des Moines, Iowa

A JOHN WILEY & SONS, INC., PUBLICATION


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Copyright © 2006 by John Wiley & Sons, Inc. 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, photocopying, recording, scanning, or otherwise, except as permitted under
Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the
Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance
Center, Inc., 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 />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 advice and strategies contained herein may not be suitable for your situation. You should
consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss
of profit or any other commercial damages, including but not limited to special, incidental, consequential, or
other damages.
For general information on our other products and services or for technical support, please contact our
Customer Care Department within the United States at (800) 762-2974, outside the United States at
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Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may
not be available in electronic formats. For more information about Wiley products, visit our web site at
www.wiley.com.
Library of Congress Cataloging-in-Publication Data:
Bloch, Heinz P., 1933–
A practical guide to compressor technology/Heinz P. Bloch.—2nd ed.
p. cm.
Includes bibliographical references and index.
ISBN-13: 978-0-471-72793-4
ISBN-10: 0-471-72793-8
1. Compressors. I. Title.
TJ990.B546 2006
621.5Ј1—dc22

2005056951
Printed in the United States of America
10

9

8

7

6

5

4

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CONTENTS

PREFACE
ACKNOWLEDGMENTS

PART I
1

POSITIVE DISPLACEMENT COMPRESSOR TECHNOLOGY

Theory
1.1
1.2
1.3
1.4
1.5

1.6
1.7
1.8
1.9
1.10
1.11
1.12
1.13

Symbols
How a Compressor Works
First Law of Thermodynamics

Second Law of Thermodynamics
Ideal or Perfect Gas Laws
1.5.1 Boyle’s Law
1.5.2 Charles’ Law
1.5.3 Amonton’s Law
1.5.4 Dalton’s Law
1.5.5 Amagat’s Law
1.5.6 Avogadro’s Law
1.5.7 Perfect Gas Formula
Vapor Pressure
Gas and Vapor
Partial Pressures
Critical Conditions
Compressibility
Generalized Compressibility Charts
Gas Mixtures
The Mole

xiii
xv

1
3
3
4
8
8
9
9
9

9
9
10
10
10
11
11
11
13
13
14
15
15
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CONTENTS

1.14 Specific Volume and Density
1.15 Volume Percent of Constituents
1.16 Molecular Weight of a Mixture
1.17 Specific Gravity and Partial Pressure
1.18 Ratio of Specific Heats
1.19 Pseudo-critical Conditions and Compressibility
1.20 Weight-Basis Items
1.21 Compression Cycles
1.22 Power Requirement
1.23 Compressibility Correction
1.24 Multiple Staging
1.25 Volume References
1.26 Cylinder Clearance and Volumetric Efficiency
1.27 Cylinder Clearance and Compression Efficiency
Reference

16
16
16
17
17
18
18
19
20
21
22
23

24
27
27

Reciprocating Process Compressor Design Overview

29

2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
2.10
2.11
2.12
2.13
2.14

33
37
37
38
39
45
47

47
48
51
55
55
56
57
59
59
61
62

Crankshaft Design
Bearings and Lubrication Systems
Connecting Rods
Crossheads
Frames and Cylinders
Cooling Provisions
Pistons
Piston and Rider Rings
Valves
Piston Rods
Packings
Cylinder Lubrication
Distance Pieces
Reciprocating Compressor Modernization
2.14.1 Cylinder Upgrades
2.14.2 Design for Easy Maintenance
2.14.3 Crosshead Designs and Attention to Reliable Lubrication
2.14.4 Materials

Reciprocating Compressor Performance and Monitoring Considerations

63

3.1

63
64
64
65
67
70
71
73

3.2
3.3

Capacity Control
3.1.1 Recycle or Bypass
3.1.2 Suction Throttling
3.1.3 Suction Valve Unloading
3.1.4 Clearance Pockets
More About Cylinder Jacket Cooling and Heating Arrangements
3.2.1 Methods of Cooling
Comparing Lubricated and Nonlubricated Conventional Cylinder
Construction
3.3.1 Lubricated Cylinder Designs
3.3.2 Nonlubricated Cylinder Design

73
75


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4

5

6

vii

3.4
3.5

Compressor Vent and Buffer Systems
Compressor Instrumentation
3.5.1 Electric vs. Pneumatic Switches
3.5.2 Switch Set Points

3.5.3 Control Panels
3.5.4 Valve-in-Piston Reciprocating Compressors
3.5.5 Barrel-Frame Reciprocating Compressors
3.6 Condition Monitoring of Reciprocating Compressors
3.6.1 Maintenance Strategies
3.6.2 Justification for Machine Monitoring
3.6.3 What to Monitor and Why
References

76
77
82
82
82
83
84
85
86
86
87
97

Labyrinth Piston Compressors

99

4.1 Main Design Features
4.2 Energy Consumption
4.3 Sealing Problems

99
101
104

Hypercompressors

109

5.1
5.2
5.3
5.4
5.5
5.6

109
111
115
117
119
120

Introduction
Cylinders and Piston Seals
Cylinder Heads and Valves
Drive Mechanism
Miscellaneous Problems
Conclusions

Metal Diaphragm Compressors

121

6.1
6.2
6.3

121
121
122

Introduction
Terminology
Description

7

Lobe and Sliding Vane Compressors

129

8

Liquid Ring Compressors

135

9

Rotary Screw Compressors and Filter Separators

141

9.1 Twin-Screw Machines
9.1.1
Working Phases
9.1.2
Areas of Application
9.1.3
Dry vs. Liquid-Injected Machines
9.1.4
Operating Principles
9.1.5
Flow Calculation
9.1.6
Power Calculation
9.1.7
Temperature Rise
9.1.8
Capacity Control
9.1.9
Mechanical Construction
9.1.10 Industry Experience

141
141
145
145
145
147

147
150
150
153
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9.1.11 Maintenance History
9.1.12 Performance Summary
Oil-Flooded Single-Screw Compressors
Selecting Modern Reverse-Flow Filter-Separator Technology
9.3.1 Conventional Filter-Separators vs. SCCs
9.3.2 Removal Efficiencies
9.3.3 Filter Quality
9.3.4 Selecting the Most Suitable Gas Filtration Equipment
9.3.5 Evaluating the Proposed Configurations
9.3.6 Life-Cycle-Cost Calculations
9.3.7 Conclusions

158
158
160
163
164

165
165
166
167
168
169

Reciprocating Compressor Performance and Sizing Fundamentals

171

10.1
10.2
10.3
10.4
10.5
10.6
10.7
10.8
10.9
10.10
10.11
10.12
10.13

172
173
174
174
176

177
177
178
178
180
181
181
182
182
182
183
183
183
184
186
187
187
187
188
188
189
189

10.14
10.15
10.16
10.17
10.18
10.19

10.20
PART II
11

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CONTENTS

9.2
9.3

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Theoretical Maximum Capacity
Capacity Losses
Valve Preload
Valve and Gas Passage Throttling
Piston Ring Leakage
Packing Leakage
Discharge Valve Leakage
Suction Valve Leakage
Heating Effects
Pulsation Effects
Horsepower
Horsepower Adders
Gas Properties
10.13.1 Ideal Gas
10.13.2 Real Gas

Alternative Equations of State
Condensation
Frame Loads
Compressor Displacement and Clearance
Staging
Fundamentals of Sizing
10.19.1 Number of Stages
10.19.2 Approximate Horsepower
10.19.3 Cylinder Bore Requirements
10.19.4 Frame Load
10.19.5 Vendor Confirmation
Sizing Examples
DYNAMIC COMPRESSOR TECHNOLOGY

197

Simplified Equations for Determining the Performance of
Dynamic Compressors

205

11.1
11.2
11.3

205
205
207

Nonoverloading Characteristics of Centrifugal Compressors

Stability
Speed Change


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11.4
11.5
12

13

Compressor Drive
Calculations

ix

207
208

Design Considerations and Manufacturing Techniques

215

12.1
12.2
12.3
12.4
12.5

Axially vs. Radially Split
Tightness
Material Stress
Nozzle Location and Maintenance
Design Overview
12.5.1 Casings
12.5.2 Flow Path
12.5.3 Rotors
12.5.4 Impellers
12.5.5 Axial Blading
12.5.6 Seals
12.6
Bearing Configurations
12.6.1 Radial Bearings
12.6.2 Thrust Bearings
12.6.3 Flexure Pivot Tilt Pad Bearings
12.7
Casing Design Criteria
12.8
Casing Manufacturing Techniques
12.9
Stage Design Considerations

12.10 Impeller Manufacturing Techniques
12.11 Rotor Dynamic Considerations
12.12 Fouling Considerations and Coatings
12.12.1 Polymerization and Fouling
12.12.2 Fouling and Its Effect on Compressor Operation
12.12.3 Coating Case Study
12.12.4 SermaLon Coating
12.12.5 Results

215
215
215
216
217
217
230
234
234
242
242
250
250
251
253
257
265
273
282
286
292

292
293
294
296
297

Advanced Sealing and Bearing Systems

299

13.1
13.2

299
300
300
302
303
304
304
308
308
310
311
311
312
314
318
318

13.3

13.4
13.5
13.6

Background
Dry Seals
13.2.1 Operating Principles
13.2.2 Operating Experience
13.2.3 Problems and Solutions
13.2.4 Dry Seal Upgrade Developments
13.2.5 Dry Gas Seal Failures Avoided by Gas Conditioning
Magnetic Bearings
13.3.1 Operating Principles
13.3.2 Operating Experience and Benefits
13.3.3 Problems and Solutions
Development Efforts
13.4.1 Thrust-Reducing Seals
Integrated Designs
Fluid-Induced Instability and Externally Pressurized Bearings
13.6.1 Instability Considerations


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13.6.2
Fluid-Induced Instability
13.6.3
Eccentricity and Stiffness
13.6.4
Externally Pressurized Bearings and Seals
13.6.5
Practical Applications
13.6.6
Rotor Model, Dynamic Stiffness, and Fluid Instability
13.6.7
Root Locus Stability Analysis
13.6.8
More About Externally Pressurized Bearings
13.6.9
Field Data Collection
13.6.10 Test Stand Data
13.6.11 Conclusions
References
Suggested Reading

318

320
321
324
325
327
328
331
334
336
336
336

Couplings, Torque Transmission, and Torque Sensing

339

14.1

339
341
343
344
345
345
347
349

Coupling Overview
14.1.1 Low Overhung Moment
14.1.2 Low Residual Unbalance Desired

14.1.3 Long Life and Maintainability
14.1.4 Continuous Lubrication Not a Cure-All
14.1.5 Contoured Diaphragm Coupling
14.2 Coupling Retrofits and Upgrades
14.3 Performance Optimization Through Torque Monitoring
15 Lubrication, Sealing, and Control Oil Systems for Turbomachinery
15.1
15.2

Considerations Common to All Systems
Seal Oil Considerations

16 Compressor Control
16.1
16.2
16.3

Introduction
Control System Objectives
Compressor Maps
16.3.1 Invariant Coordinates
16.4 Performance Control
16.4.1 PI and PID Control Algorithms
16.4.2 Stability Considerations
16.4.3 Integral or Reset Windup
16.5 Performance Limitations
16.5.1 Surge Limit
16.5.2 Stonewall
16.6 Preventing Surge
16.6.1 Antisurge Control Variables

16.6.2 Antisurge Control Algorithms
16.6.3 Controlling Limiting Variables
16.7 Loop Decoupling
16.8 Conclusions
Reference

357
357
359
363
363
363
364
366
368
370
372
373
373
374
375
376
376
378
378
379
380
380

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CONTENTS

17 Head-Flow Curve Shape of Centrifugal Compressors

18

19

xi

381

17.1
17.2

Compressor Stage
Elements of the Characteristic Shape
17.2.1
Basic Slope
17.2.2
Blade Angle
17.2.3

Fan Law Effect
17.2.4
Choke Effect
17.2.5
Mach Number
17.2.6
Significance of Gas Weight
17.2.7
Inducer Impeller Effects on Head Output
17.2.8
Surge
17.2.9
Vaned Diffusers
17.2.10 Vaneless Diffusers
17.2.11 Equivalent Tip Speeds
17.3 Conclusions

381
382
382
384
385
386
387
387
388
389
390
390
391

393

Use of Multiple-Inlet Compressors

395

18.1

Critical Selection Criteria
18.1.1
Head Rise to Surge, Surge Margin, and Overload Margin
18.1.2
Head per Section
18.1.3
Compressor Parasitic Flows
18.1.4
Excess Margins on Other Process Equipment
18.1.5
Representing Compressor Performance
18.1.6
Practical Levels of Critical Operating Parameters
18.2 Design of a Sideload Compressor
18.2.1
Mixing Area
18.2.2
Aerodynamics
18.2.3
Temperature Stratification
18.3 Testing
18.3.1

Test Setup
18.3.2
Instrumentation
18.3.3
Testing Procedure
18.3.4
Accuracy of Test Results
18.3.5
Evaluation of Results

395
396
397
398
399
399
399
401
402
403
405
405
406
406
406
407
407

Compressor Performance Testing

409

19.1

409
410
410
411
412
414
416
418
420

Performance Testing of New Compressors
19.1.1
Re-rate Options
19.1.2
General Guidelines
19.1.3
Gas Sampling
19.1.4
Instrumentation
19.1.5
Sideload Compressors
19.1.6
Calculation Procedures
19.2 Shop Testing and Types of Tests
19.3 Field Testing

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19.4

Predicting Compressor Performance at Other Than
As-Designed Conditions
19.4.1 How Performance Tests Are Documented
19.4.2 Design Parameters: What Affects Performance
19.4.3 What to Seek from Vendors’ Documents
19.4.4 Illustrations and Example
References

434
434
435
436
441

Procurement, Audit, and Asset Management Decisions

443

20.1

Incentives to Buy from Knowledgeable and Cooperative
Compressor Vendors
20.2 Industry Standards and Their Purpose
20.2.1 Typical Scope of Standards
20.2.2 Disclaimers in Standards
20.2.3 Going Beyond the Standards
20.3 Disadvantages of Cheap Process Compressors
20.4 Audits vs. Reviews
20.4.1 Staffing and Timing of Audits and Reviews
20.4.2 Use of Equipment Downtime Statistics
20.5 Auditing and Reviewing Compressors
20.6 Compressor Inspection: Extension of the Audit Effort
20.6.1 Inspection of a Welded Impeller (Wheel)
and the Entire Rotor
20.7 Compressor Installation Specifications
20.7.1 Field Erection and Installation Specifications for
Special-Purpose Machinery
References

443

Reliability-Driven Asset Management Strategies

477

21.1

Strategy for Reciprocating Compressors
21.1.1 Process Operating Window
21.1.2 Breakdown Maintenance
21.1.3 Time-Based Maintenance
21.1.4 Equipment Health Monitoring
21.1.5 Reliability and Maintenance
21.1.6 Asset Management Strategy
21.2 Achieving Compressor Asset Optimization
21.2.1 Input Obtained from Workshops
21.2.2 Conclusions
References

477
478
478
478
479
479
479
486
486
496
497

APPENDIX A PROPERTIES OF COMMON GASES

499

APPENDIX B SHORTCUT CALCULATIONS AND GRAPHICAL
COMPRESSOR SELECTION PROCEDURES

507

APPENDIX C

551

20

21

INDEX

BIBLIOGRAPHY AND LIST OF CONTRIBUTORS

432

444
444
447
447
448
449
450
450
451
465
466

474
475
476

557


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PREFACE

Compressors are a vital link in the conversion of raw materials into refined products.
Compressors also handle economical use and transformation of energy from one form into
another. They are used for the extraction of metals and minerals in mining operations, for
the conservation of energy in natural gas reinjection plants, for secondary recovery
processes in oil fields, for the utilization of new energy sources such as shale oil and tar
sands, for furnishing utility or reaction air, for oxygen and reaction gases in almost any
process, for process chemical and petrochemical plants, and for the separation and liquefaction of gases in air separation plants and in LPG and LNG plants. And, as the reader will
undoubtedly know, this listing does not even begin to describe the literally hundreds of
services that use modern compression equipment.
The economy and feasibility of all these applications depend on the reliability of compressors and the capability of the compressors selected to handle a given gas at the desired
capacity. It is well known that only turbocompressors made large process units such as
ammonia plants, ethylene plants, and base-load LNG plants technically and economically
feasible. Conversely, there are applications where only a judiciously designed positive displacement compressor will be feasible, or economical, or both. These compressors could

take the form of piston-type reciprocating machines, helical screw machines intended for
true oil-free operation, liquid-injected helical screw machines, or others. All, of course,
demand performance of the highest reliability and availability. These two requirements
form the cornerstone of the development programs under way at the design and manufacturing facilities of the world’s leading equipment producers.
Today, the petrochemical and other industries are facing intense global competition,
which in turn has created a need for lower-cost equipment. Making this equipment without
compromising quality, efficiency, and reliability is not easy, and only the industrial world’s
best manufacturers measure up to the task. Equally important, only a contemplative, informed,
and discerning equipment purchaser or equipment user can be expected to spot the right
combination of these two desirable and seemingly contradictory requirements: low cost
and high quality.
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PREFACE

The starting point of machinery selection is machinery know-how. From know-how we
can progress to type selection: reciprocating compressor vs. centrifugal compressor, dry vs.
liquid-injected rotary screw compressor. Type selection leads to component selection: oil
film seals vs. dry gas seals for centrifugal compressors. These could be exceedingly important

considerations since both type selection and component selection will have a lasting impact
on maintainability, surveillability, availability, and reliability of compressors and steam
turbines. Without fail, the ultimate effect will be plant profitability or even plant survival.
This text, then, is intended to provide the kind of guidance that will make it easier for
the reader to make an intelligent choice. Although I cannot claim it to be all-encompassing
and complete in every detail, it is nevertheless intended to be both readable and relevant.
I have brought this second edition text up to date in terms of practical, field-proven component configuration and execution of process compressors. The emphasis is on technology
for two principal categories and their respective subgroups: positive displacement compressors and dynamic compression equipment such as centrifugal and axial turbomachines.
New material deals with compressor specification, testing, reliability verification, asset
management, and related subjects.
With experience showing machinery downtime events being linked to the malfunction
of auxiliaries and support equipment, I decided to include surge suppression, lubrication
and sealing systems, couplings, and other relevant auxiliaries. All of these are thoroughly
cross-referenced in the index and should be helpful to a wide spectrum of readers.
While compiling this information from commercially available industry source materials, I was struck by the profusion of diligent effort that some manufacturers have expended
to design and manufacture more efficient, more reliable machinery. With much of this source
material dispersed among the various sales, marketing, design, and manufacturing groups,
I set out to collect the data and organize it into a book that first acquaints the reader with
the topic by using overview and summary-type materials. The information progresses
through more detailed and somewhat more design-oriented write-ups toward scoping studies and application and selection examples. Some of these are shown in both English and
metric units; others were left in the method chosen by the original contributor.
The reader will note that I stayed away from an excessively mathematical treatment of the
subject at hand. Instead, the focus was clearly on giving a single-source reference on all that
will be needed by the widest possible spectrum of machinery users, ranging from plant operators to mechanical technical support technicians, reliability engineers, mechanical and chemical engineers, operations superintendents, project managers, and senior plant administrators.
The publishers and I wish to point out that the book would never have been written without the full cooperation of a large number of highly competent equipment manufacturers in
the United States and overseas. It was compiled by obtaining permission to use the direct
contributions of companies and individuals listed in the acknowledgments. These contributions were then structured into a cohesive survey of what the reader should know about
compressor technology in the year 2006. The real credit should therefore go to the various
contributors, not to the coordinating or compiling editor. In line with this thought, I would
be most pleased if the entire effort would serve to acquaint the reader not only with the

topic, but also with the names of the outstanding individuals and companies whose contributions made it all possible.
HEINZ P. BLOCH
West Des Moines, Iowa


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ACKNOWLEDGMENTS

We gratefully acknowledge the cooperation and, in many cases, intense special effort of the
companies and individuals whose contributions to this book made the entire endeavor possible in the first place. Others have been timely, diligent, and kind to both review this material and secure permission for its incorporation in the book.
Our special thanks go to A-C Compressor Corporation, Appleton, Wis.; Aerzen USA
Company and Pierre Noack, Coatesville, Pa.; Anglo Compression, Inc., Mount Vernon,
Ohio; The American Society of Mechanical Engineers, New York, N. Y.; Bently-Nevada
Corporation, Minden, Nev.; BHS-Voith Getriebewerke, Sonthofen, Germany; Burckhardt
Compression AG, Winterthur, Switzerland; Cooper Industries, Mount Vernon, Ohio;
Compressor Controls Corporation and Dr. B. W. Batson, Des Moines, Iowa; Coupling
Corporation of America, Jacobus, Pa.; John Crane Company and Joe Delrahim, Morton Grove,
Ill.; Demag Delaval Turbomachinery and Ken Reich, Gary Walker, and Roy Salisbury, Trenton,
N.J.; Dresser Industries, Inc., Roots Division, Connersville, Ind.; Dresser-Rand Company,
Engine Process Compressor Division and Ron Beyer, G. A. Lentek, Martin Hinchliff, and Dick
Schaad, Painted Post, N.Y.; Dresser-Rand Turbo Products and Harvey Galloway, Russ
Svendsen, and Art Wemmell, Olean, N.Y.; Elliott Company and Ross A. Hackel, Don Hallock,
and Ken Peters, Jeannette, Pa.; Flexelement Texas, Houston, Tex., and Michael Saunders;

Flexibox, Inc., Houston, Tex.; Imo Industries (now Mannesmann-Demag-DeLaval), Trenton,
N.J.; Indikon/Metravib Instruments, Cambridge, Mass.; King Tool Company and Dale
Sweeney, Longview, Tex.; Bearings Plus, Inc., and Dr. Fouad Zeidan, Houston, Tex.; Lincoln
Division of McNeil Corporation, St. Louis, Mo.; Lubrication Systems Company, Houston,
Tex.; Lubriquip, Inc., Cleveland, Ohio; Lucas Aerospace Company, Bendix Fluid Power
Division, Utica, N.Y.; Nash Engineering Company, Norwalk, Conn.; M. T. Gresh of Flexware,
Inc., Jeannette, Pa.; Nuovo Pignone, Florence, Italy; Pressure Products Industries Division, The
Duriron Company, Warminster, Pa.; Pressurized Bearing Co. and Donald Bently and Carlo
Luri, Minden, Nev.; Prognost Systems and Thorsten Bickmann and Eike Drewes, Rheine,
Germany; Revolve Technologies and Paul Eakins, T. J. Al-Himyary, and Stan Uptigrove,
Calgary, Alberta, Canada; Rotordynamics-Seal Research, North Highlands, CA; Sermatech,
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ACKNOWLEDGMENTS

Pottstown, Pa.; Shiraz Pradhan, Pradhan Core Engineering, Baytown, Tex.; SulzerBurckhardt Engineering Works, Ltd., Winterthur, Switzerland; Sulzer Turbosystems
International and Bernhard Haberthuer and Chris Rufer, New York, N.Y.; Torquetronics,
Alleghany, N.Y.; and Zurn Industries, Erie, Pa.
Also, many thanks to the individual contributors: Mike Calistrat (Section 14.1);

R. Chow, B. McMordie, and R. Wiegand (Section 12.2.1), Arvind Godse (Section 19.4),
Claude Matile (we decided his contribution of Chapter 5 is a stand-alone classic that should
remain unchanged), and John Mitchell (Section 21.2).


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PART I
POSITIVE DISPLACEMENT
COMPRESSOR TECHNOLOGY

Positive displacement compressors comprise the first of the two principal compressor categories, the second being dynamic compressors. In all positive displacement machines, a
certain inlet volume of gas is confined in a given space and subsequently compressed by
reducing this confined space or volume. At this now elevated pressure, the gas is next expelled
into the discharge piping or vessel system.
Although positive displacement compressors include a wide spectrum of configurations
and geometries, the most important process machines are piston-equipped reciprocating
compressors and helical screw rotating machines. Although there are a number of others,
including diaphragm and sliding vane compressors, the overwhelming majority of significant
process gas-positive displacement machines are clearly reciprocating piston and twin helical
screw-rotating or rotary screw machines. For that reason, this book focuses on their operating
characteristics and application ranges. Figure I.1 identifies these application ranges and allows
us to compare typical flow and pressure fields for other compressor types as well.
A1

A2
B
C
D
E
F
G

reciprocating compressors with lubricated and nonlubricated cylinders
reciprocating compressors for high and very high pressures with lubricated
cylinders
helical- or spiral-lobe compressors (rotary screw compressors) with dry or
oil-flooded rotors
liquid ring compressors (also used as vacuum pumps)
two-impeller straight-lobe rotary compressors, oil-free (also used as vacuum
pumps)
centrifugal turbocompressors
axial turbocompressors
diaphragm compressors

A Practical Guide to Compressor Technology, Second Edition, By Heinz P. Bloch
Copyright © 2006 John Wiley & Sons, Inc.

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POSITIVE DISPLACEMENT COMPRESSOR TECHNOLOGY

FIGURE I.1 Application ranges for various types of compressors. (Sulzer-Burckhardt, Winterthur
and Basel, Switzerland)

The most frequently used combinations of two different compressor types are identified in
three fields:
A ϩ G oil-free reciprocating compressor followed by a diaphragm compressor
E ϩ A centrifugal turbocompressor followed by an oil-free reciprocating
compressor
F ϩ E axial turbocompressor followed by a centrifugal turbocompressor


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1
THEORY*

This discussion of thermodynamics is limited to the processes that are involved in the compression of gases in a positive displacement compressor of the reciprocating type. A positive displacement compressor is a machine that increases the pressure of a definite initial
volume of gas, accomplishing the pressure increase by volume reduction. Only with a
knowledge of basic laws and their application can one understand what is happening in a
compressor and thus properly solve any compression problem.
The definitions and units of measurement given at the end of this chapter should either
be known to the reader or be reviewed thoroughly before beginning.

1.1

SYMBOLS

The following symbols (based on pounds, feet, seconds, and degrees Fahrenheit) are used
in this discussion of positive displacement compressor theory:
c
cp
cv
CE
k
M
ME
N

cylinder clearance, % or decimal
specific heat-constant pressure, Btu/°F-lb
specific heat-constant volume, Btu/°F-lb
compression efficiency, %
ratio of specific heats, dimensionless
molecular weight (MW), dimensionless
mechanical efficiency, %
number of moles, dimensionless

* Developed and contributed by Dresser-Rand Company, Olean, N.Y. Based on Ingersoll-Rand Form 3519-D.
A Practical Guide to Compressor Technology, Second Edition, By Heinz P. Bloch
Copyright © 2006 John Wiley & Sons, Inc.

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THEORY

Na,b,c
p
pa,b,c
pa
pc
pr
ps
pv
psia
psig
Pt
Q

r
rt
R0
RЈ
RH
s
S
SH
SPT
T
Tc
Tr
v
va,b,c
vr
V
VE
W
Wa
Wv
Wa,b,c
Z
␩v

1.2

Page 4

moles of constituents, dimensionless
pressure, psia

partial pressure of constituents, psia
partial air pressure, psia
critical pressure (gas property), psia
reduced pressure, dimensionless
saturated vapor pressure, psia or in. Hg
partial vapor pressure, psia or in. Hg
lb/in2 absolute, psi
lb/in2 gauge, psi
theoretical horsepower, (work rate), hp
heat, Btu
ratio of compression per stage, dimensionless
ratio of compression—total, dimensionless
universal or molar gas constant, ft-lb/mol-°R (1545 when p is in lb/ft2)
specific gas constant, ft-lb/lb-°R
relative humidity, %
number of stages of compression, dimensionless
entropy, Btu/lb-°F
specific humidity, lb moisture/lb dry gas
standard pressure and temperature, 14.696 psia and 60°F
absolute temperature, °R
critical temperature, °R
reduced temperature, dimensionless
specific volume, ft3/lb
partial volume of constituents, ft3/lb
pseudo-specific reduced volume, ft3/lb
total volume, ft3
volumetric efficiency, %
weight, lb
weight of dry air in a mixture, lb
weight of vapor in a mixture, lb

weight of constituents in a mixture, lb
compressibility factor, dimensionless
volumetric efficiency, %

HOW A COMPRESSOR WORKS

Every compressor is made up of one or more basic elements. A single element, or a group
of elements in parallel, comprises a single-stage compressor. Many compression problems
involve conditions beyond the practical capability of a single compression stage. Too great
a compression ratio (absolute discharge pressure divided by absolute intake pressure)
causes excessive discharge temperature and other design problems. It therefore may
become necessary to combine elements or groups of elements in series to form a multistage
unit, in which there will be two or more steps of compression. The gas is frequently cooled
between stages to reduce the temperature and volume entering the following stage.


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HOW A COMPRESSOR WORKS

5

Note that each stage is an individual basic compressor within itself. It is sized to operate in series with one or more additional basic compressors, and even though they may all
operate from one power source, each is still a separate compressor.

The basic reciprocating compression element is a single cylinder compressing on only one
side of the piston (single-acting). A unit compressing on both sides of the piston (doubleacting) consists of two basic single-acting elements operating in parallel in one casting.
The reciprocating compressor uses automatic spring-loaded valves that open only when
the proper differential pressure exists across the valve. Inlet valves open when the pressure
in the cylinder is slightly below the intake pressure. Discharge valves open when the pressure in the cylinder is slightly above the discharge pressure.
Figure 1.1 shows the basic element with the cylinder full of a gas, say, atmospheric air.
On the theoretical p–V diagram (indicator card), point 1 is the start of compression. Both
valves are closed.
Figure 1.2 shows the compression stroke, the piston having moved to the left, reducing
the original volume of air with an accompanying rise in pressure. Valves remain closed.
The p–V diagram shows compression from point 1 to point 2, and the pressure inside the
cylinder has reached that in the receiver.
Figure 1.3 shows the piston completing the delivery stroke. The discharge valves opened
just beyond point 2. Compressed air is flowing out through the discharge valves to the
receiver. After the piston reaches point 3, the discharge valves will close, leaving the clearance space filled with air at discharge pressure.
During the expansion stroke (Fig. 1.4) both the inlet and discharge valves remain closed,
and air trapped in the clearance space increases in volume, causing a reduction in pressure.
This continues as the piston moves to the right, until the cylinder pressure drops below the
inlet pressure at point 4.

FIGURE 1.1 Basic compressor element with the cylinder full of gas. On the theoretical p–V diagram
(indicator card), point 1 is the start of compression. Both valves are closed. (Dresser-Rand Company,
Painted Post, N.Y.)


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THEORY

FIGURE 1.2 Compression stroke. The piston has moved to the left, reducing the original volume
of gas with an accompanying rise in pressure. Valves remain closed. The p–V diagram shows compression from point 1 to point 2 and the pressure inside the cylinder has reached that in the receiver.
(Dresser-Rand Company, Painted Post, N.Y.)

FIGURE 1.3 The piston is shown completing the delivery stroke. The discharge valves opened just
beyond point 2. Compressed air is flowing out through the discharge valves to the receiver. (DresserRand Company, Painted Post, N.Y.)

The inlet valves will now open, and air will flow into the cylinder until the end of the
reverse stroke at point 1. This is the intake or suction stroke, illustrated by Fig. 1.5. At point
1 on the p–V diagram, the inlet valves will close and the cycle will repeat on the next revolution of the crank.
In an elemental two-stage reciprocating compressor the cylinders are proportioned
according to the total compression ratio, the second stage being smaller because the gas,


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7

FIGURE 1.4 During the expansion stroke shown, both the inlet and discharge valves remain closed
and gas trapped in the clearance space increases in volume, causing a reduction in pressure. (DresserRand Company, Painted Post, N.Y.)

FIGURE 1.5 At point 4, the inlet valves will open and gas will flow into the cylinder until the end
of the reverse stroke at point 1. (Dresser-Rand Company, Painted Post, N.Y.)

having already been partially compressed and cooled, occupies less volume than at the
first-stage inlet. Looking at the p–V diagram (Fig. 1.6), the conditions before starting compression are points 1 and 5 for the first and second stages, respectively; after compression,
conditions are points 2 and 6, and after delivery, points 3 and 7. Expansion of gas trapped
in the clearance space as the piston reverses brings points 4 and 8, and on the intake stroke
the cylinders are again filled at points 1 and 5 and the cycle is set for repetition. Multiple
staging of any positive displacement compressor follows this pattern.
Certain laws that govern the changes of state of gases must be thoroughly understood.
Symbols were listed in Section 1.1.


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THEORY

FIGURE 1.6
Post, N.Y.)

1.3

The p–V diagram for a two-stage compressor. (Dresser-Rand Company, Painted

FIRST LAW OF THERMODYNAMICS

The first law of thermodynamics states that energy cannot be created or destroyed during a
process (such as compression and delivery of a gas), although it may change from one form
of energy to another. In other words, whenever a quantity of one kind of energy disappears,
an exactly equivalent total of other kinds of energy must be produced.

1.4

SECOND LAW OF THERMODYNAMICS

The second law of thermodynamics is more abstract and can be stated in several ways.
1. Heat cannot, of itself, pass from a colder to a hotter body.
2. Heat can be made to go from a body at lower temperature to one at higher temperature only if external work is done.
3. The available energy of the isolated system decreases in all real processes.
4. Heat or energy (or water), of itself, will flow only downhill.
Basically, these statements say that energy exists at various levels and is available for use
only if it can move from a higher to a lower level.
In thermodynamics a measure of the unavailability of energy has been devised and is
known as entropy. It is defined by the differential equation
dS ϭ d

Q
T

(1.1)

Note that entropy (as a measure of unavailability) increases as a system loses heat but
remains constant when there is no gain or loss of heat (as in an adiabatic process).