Valve Handbook

372 Pages·2005·13.17 MB·English

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Valve Handbook

Philip L. Skousen
Valtek International

McGraw-Hill

New York
San Francisco
Washington.
D.C.
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.Bogota
Caracas
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Con ten ts

Preface
ix
Acknowledgments
xiii

Chapter 1. Introduction to Valves
1

1.1 The Valve
1
1.2 The History of Valves
2
1.3 Valve Classification According to Function
7
1.4 Classification According to Application
13
1.5 Classification According to Motion
16
1.6 Classification According to Port Size
16
1.7 Common Piping Nomenclature
17

Chapter 2. Valve Selection
Criteria
21

2.1 Valve Coefficients
21
2.2 Flow Characteristics
22
2.3 Shutoff Requirements
36
2.4 Body End Connections
37
2.5 Pressure Classes
47
2.6 Face-to-Face Criteria
49
2.7 Body Material Selection
50
2.8 Gasket Selection
58
2.9 Packing Selection
65

vi
Contents

Chapter 3. Manual Valves
85

3.1 Introduction
to Manual Valves
85
3.2 Manual Plug Valves
87
3.3 Manual Ball Valves
101
3.4 Manual Butterfly Valves
111
3.5 Manual Globe Valves
132
3.6 Manual Gate Valves
147
3.7 Manual Pinch Valves
161
3.8 Manual Diaphragm Valves
170

Chapter 4. Check Valves
177

4.1 Introduction
to Check Valves
177
4.2 Lift Check Valves
179
4.3 Swing Check Valves
188
4.4 Tilting-Disk Check Valve
192
4.5 Double-Disk Check Valves
198
4.6 Diaphragm Check Valves
204

Chapter 5. Pressure Relief Valves
209

5.1 Introduction
to Pressure
Relief Valves
209

Chapter 8. Control Valves
221

6.1 Introduction
to Control Valves
221
6.2 Globe Control Valves
222
6.3 Butterfly Control Valves
261
6.4 Ball Control Valves
285
6.5 Eccentric Plug Control Valves
305

Chapter 7. Manual Operators and Actuators
321

7. 1 Introduction
to Manual Operators and Actuators
321
7.2 Manual Operators
324
7.3 Pneumatic Actuators
335
7.4 Nonpneumatic
Actuators
363
7.5 Actuator Performance
369
7.6 Positioners
370
7.7 Auxiliary Handwheels
376
7.8 External Failure Systems
384
7.9 Common Accessories
390
7.10 Electrical Equipment Certifications
403

Contents
vii

Chapter 8. Smart Valves and Positioners
411

8.1 Process Control
411
8.2 Intelligent Systems for Control Valves
417
8.3 Digital Positioners
423

Chapter 9. Valve Sizing
429

9.1 Introduction
to Valve Sizing
429
9.2 Valve-Sizing Nomenclature
433
9.3 Body Sizing of Liquid-Service Control Valves
439
9.4 Body Sizing of Gas-Service Control Valves
458
9.5 Pressure-Relief-Valve Sizing
471

Chapter 10. Actuator Sizing
479

10.1 Actuator-Sizing
Criteria
479
10.2 Sizing Pneumatic Actuators
487
10.3 Sizing Electromechanical
and Electrohydraulic
Actuators
497

Chapter 11. Common-Valve Problems
499

11.1 High-Pressure
Drops
499
11.2 Cavitation
503
11.3 Flashing
526
11.4 Choked Flow
528
11.5 High Velocities
529
11.6 Water-Hammer
Effects
530
11.7 High Noise Levels
531
11.8 Noise Attenuation
552
11.9 Fugitive Emissions
573

Chapter 12. Valve Purchasing
Issues
595

12.1 Life-Cycle Costs
595
12.2 Spare Parts
599

Bibliography
809

Appendix A. Common Conversion Factors
813

Appendix B. Fluid Data
837

viii
Contents

Appendix C. Method 21-Determination
of Volatile Organic CompoundLeaks
857

Abbreviations of Related Organizations
and Standards
885

Glossary
887

Index
709

Preface

The editors at McGraw-Hill first approached
me about writing this
handbook
nearly three years ago, after reviewing an article that I
authored for The Valve Magazine. They indicated that they were inter-
ested in having me author a valve handbook,
using my common
denominator writing style. I liked the challenge that they proposed,
and I accepted. Now, after literally hundreds
of hours, dozens of
phone calls and facsimiles, and four drafts, the handbook is ready for
the valve-using public.
When I began my career with Valtek International in 1975,I was like
many who have started out in this industry: My only experience with
a valve was taking a pair of pliers to a leaky faucet in the bathroom.
But spending three years in the engineering department at Valtek and
then some 18 years as a technical communicator
cured me of the
notion that a process valve is just a larger version of a simple faucet.
True, the two are related in a number of ways and they both work by
the same scientific principles. However, the engineering design and
complexity of process valves can be immense. The process services
they are installed
in can sometimes
be brutal-even
capable
of
destroying a valve in hours if misapplied. To me this is an exciting and
dynamic industry, especially with the advent of smart technology,
which has lifted the science and application of valves to a whole new
level.
Twenty years ago, when I first picked up a drawing pencil (yes,
computer-aided design was still a couple years away), if one wanted

Ix

]I[
Preface

to find basic information about valves, not much was readily available.
Unfortunately, if a person starting out in the valve business or process
industry wanted to learn the basics about valves, instead of turning to
a good reference handbook, he or she had to ask questions of more
senior engineers or technicians. More often than not, the individual
might not have had the educational background or experience to even
ask the right questions. Hence, learning the basics of valves often took
months and maybe even years to fully understand certain designs and
principles.
It's not that valve books didn't
exist; they did then and still do
today. The problem is that such books do not typically address the
questions or level of understanding
that most nonvalve experts ask. A
few valve books existed, but none began with the simple concepts of
fluid dynamics and valve design to build a foundation
of common
understanding
between the reader and the author. Once this founda-
tion is established, the more complex issues can then be addressed.
Those valve books in existence were primarily authored by one or sev-
eral of the industry "gurus" or experts. Many were product specific,
such as those experts in severe service trims, packing boxes, or actua-
tors. Others had studied the adverse effects of process flow, such as
those who extensively studied cavitation or noise. Some handbooks
were com.piled from aseries of "white papers" from a wide assortment
of experts and brought together by an independent
editor-a
great
method to put out a high level of knowledge quickly, but lacking in
continuity and basics. While most books concentrated on design and
severe services,
little information
was provided
about selection
options, or about installing, starting up, troubleshooting, and servicing
valves.
Over the years, I've had the opportunity
to meet and work with
many of these valve experts. I have a great respect for their knowledge
and pioneering efforts in the field of valves. The knowledge that such
experts impart is important to the entire industry. Once understood by
the user, it can help solve application and process control questions. A
problem inherent with many authors and some industry
experts is
their basic assumption that the reader knows as much as the author-
or that at least the author and reader have the same high level of
understanding
or engineering background. Although that may be fine
for those experienced in the industry over some 10 or 20 years or with
advanced engineering degrees, it leaves a great many people out of the
loop of understanding. I decided to write this book for those who need
to know the essence of valves and know it quickly. In this day of cor-
porate turnarounds or internal reengineering, the ability to understand

Preface
xi

a particular segment of process control-such
as valves-cannot
wait
for a decade of experience. Engineers and technicians responsible for
valves need knowledge now-knowledge
that is simple to understand
and easy to apply. After the basics are understood, the finer parts of
this business can then be explored, some of which are explained in this
handbook, as well as other valve books.
As a certified business communicator, one with years of technical
writing and editing about valves, I have learned that the best approach
to communication is to begin simply and write to a common denomi-
nator. This means that if a principle or concept is written to a high
school level, both the high school graduate and the engineer with a
masters degree will understand it. But if that same concept is written
to a higher level, such as a 16th grade level, only the university gradu-
ate will understand it. That's not to say that higher knowledge in this
book is missing or "dumbed
down." Rather, this higher degree of
information is presented in a structured, simplified manner with no
assumptions
of knowledge
made. Because of this style, if the user
reads this handbook from cover to cover, he or she may find some
duplication of information. This is because most handbooks, like ency-
clopedias and dictionaries, are used for reference purposes: they sit on
a shelf until they are needed to answer a particular
question or to
explain a particular
concept. With common denominator
style, the
reader will be able to turn to any section of the handbook, read it, and
understand the concepts ...without keeping a finger glued to the glos-
sary or the index, or left wondering about a term.
With my experience in referencing valve books, I have learned one
important fact: This industry is so large that no one book could ever
hope to contain every fact, design concept, sizing equation, or princi-
ple about the thousands of different valve models available today. If
possible, the book would become a set of 20 volumes, and then be so
massive that the user would find it extremely cumbersome.
As I accepted
this challenge
of writing
a valve handbook
for
McGraw-Hill, I took the approach that a dozen basic designs and a
handful of scientific principles represent the foundation of the valve
industry. Taking into account the dozens of valve manufacturers, each·
design can have literally hundreds of particular features. Rather than
research and include them all, I have opted to take the most common
features and have described them in detail. A number of statements
are made in the book describing the general design of a particular
valve design or feature. Because no one rule can be steadfast in this
dynamic business, these general statements are by no means certain or
definite. Exceptions can always be found to these general statements.

xii
Prtf'ao.

This also applies to any information in the handbook about in.taUa-
tion, quick-checking, troubleshooting, and servicing of a valve. Th••e
sections are provided as general guidelines to the user, compUed from
various users and manufacturers. In no way can they possibly apply to
every type of valve and are certainly not intended to replace th. man·
ufacturer's
technical and maintenance
literature.
By inc1udin.
thie
information, I hope that these tips and ideas will provide the Ult' with
a broader base of information than may be provided by the manufac·
turer's literature alone.
The terminology used in the book is based upon my experi.nc.
and
the advice of others. With the wide diversity represented by th. valv•. ' .
industry, I found the same valve part or concept can be caUed by d\Nt,
or four different names. In the introduction of a new term, I hav._
included other common names for reference purposes. How.v.r,
I UM
the first term consistently throughout the entire handbook. Thi. i. not
to say that the other terms are incorrect. Rather, I believe that I con••••
tency of terminology makes the concepts and designs easier to under-
stand ..
Some of the information
contained
in this book has com. to •••
through technical materials, training manuals, or white pap.n
that 'I
have collected over the years. In addition, dozens of valve manufac-
turers graciously responded to my initial request for information aNi
sent me boxes of material. In some cases, I have relied upon my own
knowledge and experience with valves, as well as my interview. wi.
dozens of users over the years. Overall, I was impressed with much 01
the recent material produced by valve manufacturers. Many hav•• oM
to great lengths to portray their products with simple, easy-to-undlr-
stand concepts ..
Because my primary focus in valves has been control valv•• , I1m
indeed grateful to those experts in the manual, check, and pJ'lIlUJ'l
relief valve industries who patiently explained the finer pointa of tMAr
products to me. I am also grateful for their review of my material, a.
well as their suggestions and criticisms. One thing I have learned from
authoring
this handbook
is that a great number
of opinions
exist
among the valve experts of today. Although I respect all opinions and
arguments offered to me as part of this project, in some cases I had to
act as referee when two opinions conflicted. In such situations,
the
decision to promote one idea over another was based upon my judg-
ment and the opinions of several leaders whose judgment I have come
to trust.

Philip L. Skousen

AcknowledgIIlen ts

Over the past two years, a great number of individuals have assisted
the author with the preparation of this handbook, sharing their knowl-
edge of particular portions of the valve industry, including the design,
operation,
troubleshooting,
and service of a wide range of process
valves. These individuals have not only provided valuable input, but
have also reviewed portions of the manuscript and recommended clar-
ifications, which have been extremely valuable. Many of these individ-
uals also provided the photography, artwork, illustrations, graphs, and
table data-greatly
adding to the content of the handbook.
Special thanks
to: Mark Peters of Accord Controls
(Cincinnati,
Ohio), a subsidiary of the Duriron Company; Tim Martin of Adams
(Houston, Texas); Peter Amos and John Stofira of Advanced Products
Company
(North Haven,
Connecticut);
Roland Larkin and C. H.
Lovoy of the American Flow Control, a division of American Cast Iron
Pipe
(Birmingham,
Alabama);
Bill Knecht
of Anchor/Darling
(Williamsport, Pennysylvania); Chris Buxton and Michelle Strauss of
Anderson,
Greenwood
& Co. (Houston,
Texas), a subsidiary
of
Keystone International, Inc.; Richard H. Stern of the Automatic Switch
Company
(Florham Park, New Jersey); Richard Weeks of Automax
(Cincinnati,
Ohio), a subsidiary
of The Duriron
Company;
Dan
Wisenbaker of Betis Actuators
and Controls (Waller, Texas); Fermo
Gianesello, Robert Katz, Herb Miller, Andrew Noakes, and Nicole
Woods of Control
Components
Inc. (Rancho
Santa
Margarita,
California);
Nancy Winalski of Conval Inc. (Somers, Connecticut);

xiii

xiv
Acknowledgments

Walter W. Mott of Copes-Vulcan
(Lake City, Pennsylvania);
Lew
Babbidge and Cindy Sartain of the Daniel Valve Company, a division
of Daniel Industries, Inc. (House ton, Texas); Jean Surma of DeZURIK
(Sartell, Minnesota); Rom Bordelon of Dresser Industries
(Alexandria,
Lousiana); Ken Senior of the DuPont Company-Polymers
(Newark,
Delaware); Dennis Garber of Durco Valve (Cookeville, Tennessee), a
subsidiary of the Duriron Company; Philip R. Vaughn of DynaTorque
Valve Actuators
and Accessories (Muskegon,
Michigan); Bob Sogge
and John Wells of Fisher
Controls
(Marshalltown,
Iowa);
Susan
Anderson
of Flowseal (Long Beach, California),
a division of Crane
Valves; Lee Ann McMurtrie
of the Groth Corporation
(Houston,
Texas); James D. Phillips of the Gulf Valve Company (Houston, Texas);
Will Gavin of the Hydroseal Valve Company, Inc. (Kilgore, Texas); Lou
Gaudio
and Valerie D. Litz of ITT Engineered
Valves; Ian W. B.
Johnson
of Kammer Ventile (Essen, Germany),
a subsidiary
of the
Duriron
Company;
Domenic DiPaolo of Kammer USA (Pittsburgh,
Pennsylvania), a subsidiary of The Duriron Company; Carter Hydrick
of Keystone International,
Inc. (Houston, Texas); Robert Hoffman of
Mueller Steam Specialty (St. Pauls, North Carolina); Jime Holmes of
Parker Electrohydraulics
(Elyria, Ohio); Michael Fitzpatrick
of Orbit
Valve Company
(Little Rock, Arkansas);
Susan Anderson
of Pacific
Valves (Long Beach, California),
a division
of Crane Valves; Christ
Letzelter of the Red Valve Company (Pittsburgh, Pennsylvania); Kevin
Speed of Jordan Valve (Cincinnati, Ohio), a division of the Richards
Industries Valve Group; Chris Warnett of Rotork Actuation (Rochester,
New York); Pierre Brooking of Sereg Vannes (Paris, France), a sub-
sidiary
of The Duriron
Company;
Stephen R. Gow of Spirax Sarco
(Allentown, Pennsylvania);
Frank Breinholt, Fred Cain, Candee Ellis,
Alan Glenn, and Craig Heraldson of Valtek International
(Springville,
Utah), a subsidiary of the Duriron Company; Bill Sandler of the Valve
Manufacturers
Association
of America (Washington,
D.C.); Deborah
Lovegrove
and Tom Velan of Velan Valve Corporation
(Williston,
Vermont); Gilbert K. Greene of the Victaulic Company
of America
(Easton,
Pennsylvania);
John J. Murphy
of Yarway
(Blue Bell,
Pennsylvania), a subsidiary of Keystone International Inc.
I would also like to thank my employer, Valtek International,
for its
valuable assistance and support during this two-year project. Twelv~
years ago, as a technical communicator
for Valtek, I was given the
assignment to author a sizing and selection guide for control valves,
working with a number of excellent engineers who helped guide me
through that 200-page document. It was during that time that I first
envisioned a handbook that would explain valves in a simple, straight-

Acknowledgments
XV

forward manner. Valtek's parent company, The Duriron Company, Inc.,
took a special interest in this project-in
partiular Duriron's chairman
and CEO Bill Jordan. Bill supported
this project from day one and
encouraged me to complete it, for which I am grateful.
And, finally, I'd like to thank my wife, Patty, for her general support
and assistance with proofreading
the manuscript. Her insightful com-
ments and objectivity helped make this handbook what it is. I am also
thankful for my three daughters-Lindsay,
Ashlee, and Kristin-who
saw a little less of their dad during this project and were very under-
standing (well, mostly understanding)
when I needed to use the home
computer. It's all yours now, girls!

Valve Handbook

1
Introduction
to Valves

1.1
The Valve
1.1.1
Definition of a Valve

By definition,
valves are mechanical devices specifically designed to
direct, start, stop, mix, or regulate the flow, pressure, or temperature of
a process fluid. Valves can be designed to handle either liquid or gas
applications.
By nature of their design, function, and application, valves come in a
wide variety of styles, sizes, and pressure classes. The smallest indus-
trial valves can weigh as little as 1 lb (0.45 kg) and fit comfortably in
the human hand, while the largest can weigh up to 10 tons (9070 kg)
and extend in height to over 24 ft (6.1 m). Industrial process valves can
be used in pipeline sizes from 0.5 in [nominal diameter (ON) 15] to
beyond 48 in (ON 1200),although over 90 percent of the valves used in
process systems are installed in piping that is 4 in (ON 100) and small-
er in size. Valves can be used in pressures from vacuum to over 13,000
psi (897 bar). An example of how process valves can vary in size is
shown in Fig. 1.1.
Today's spectrum
of available valves extends from simple water
faucets to control valves equipped with microprocessors,
which pro-
vide single-loop control of the process. The most common types in use
today are gate, plug, ball, butterfly, check, pressure-relief,
and globe
valves.
Valves can be manufactured
from a number of materials, with most
valves made from steel, iron, plastic, brass, bronze, or a number of
special alloys.

1

1.2
The History of Val.•.••
1.2.1
Earliest Use of the VaIN

Prior to the development of even .imple irrigation systems, crops cul-
tivated by early civilizations were at the mercy of whims of weather,
water levels of rivers or lakes, or the strength of humans and animals
to transport water in primitive vessels. Because of the unpredictability
or hardship
associated
with thete methods, early farmers sought a
number of ways to control the flow of nearby water sources.
The primary ideal of a valve most likely arose when these simple
farmers noticed that fallen tree. or debris diverted, or even stopped,
the flow of streams; thus the concept arose of using artificial barriers
to divert water into nearby fields. Eventually, this idea expanded into
simple irrigation using a planned series of ditches and canals, which
by using gravity could transport,
store, and widen the reach of the
water source.
An important element of these early irrigation systems was a remov-
able wooden or stone barrier, which could be placed at the entrance of
each irrigation channel. This barrier was the early progenitor of what
we now commonly call the gate valve and could be wedged between

Introduction
to Valves
3

the walls of a canal to stop the flow or divert the flow to other chan-
nels, or when placed in a position between shut and fully open could
regulate the amount of water entering the channel downstream.
As early as 5000 BC, crude gate valves were found in a series of dikes
designed
as part of ancient
irrigation
systems
developed
by the
Egyptians
along the banks of the Nile River. Archaeologists
have
found
that other ancient
cultures
in Babylon,
China,
Phoenicia,
Mexico, and Peru also used'similar irrigation systems.
As early engineers examined these primitive process systems, they
began to apply the technology to new uses. For example, as early as
1500 BC, the tombs of Egypt were equipped with extensive drainage
systems, which included
siphons, bellows, and simple plug valves
carved from wood. Designed to bring water to the surface from under-
ground wells, sophisticated
saqqiehs in Egypt were equipped
with
simple wooden valves in the buckets used to transport the water.
The Romans, having conquered the Middle East, quickly saw the
value of the Middle Eastern hydraulic engineering and expanded the
concept into a series of aqueducts in Europe, which were used to sus-
tain new cities that were located in areas away from major water
sources. These aqueducts included early pumps, piping, and water-
wheels, as well as gate and plug valves made of wood, stone, or lead.

1.2.2
Historical Development
of the Valve

Generally, valves during the Middle Ages were crude, carved from
wood, and used mainly as bungs in wine and beer casks. Valve design
changed very little until the Renaissance when modern hydraulic engi-
neering principles began to evolve. In an attempt to improve the per-
formance of canal locks, Leonado da Vinci analyzed the stresses that
would occur at different lock gates with varying heights of water on
either side of the gate. These early studies of the concept of pressure
drop helped determine the basis for modern fluid dynamics, which is
essential to understanding
and calculating the performance of valves.
In 1712, Englishman Thomas Newcomen invented his atmospheric
engine (sometimes called a heat engine), which used low-pressure steam
to drive a piston forward. When attached to a pivot beam, this simple
engine
could be used to lift water. As Newcomen
improved
his
machine, he introduced a simple iron plug valve, which could be used
to regulate the flow of steam to the piston-the
first known applica-
tion of a throttling valve.

4
Chapter One

In the late 1700s, the pioneering Scottish engineer James Watt looked
for ways to improve Newcomen's atmospheric engine. Watt examined
a number of ways to improve the Newcomen
machine, which was
slow and not very powerful because of the low-pressure steam. Also,
because of the single-direction action, each stroke had to be returned
to position by counterweights, which was extremely inefficient. Watt's
final redesign of the inefficient Newcomen
engine evolved into the
first double-acting
engine. Watt's engine introduced
steam to both
sides of the piston, driving both the upstroke and downstroke simulta-
neously. A piston rod was attached to both sides of a crank to produce
rotary motion for driving wheels, which finally led to the development
of steam locomotives and steamboats. Critical to Watt's steam engine
were self-acting valves, which were used to introduce and vent steam
from both sides of the piston. Although these iron valves were crude
by today's standards, their function was critical to the success of the
steam engine, which ushered in the Industrial Age.
During the 1800s the use of steam power in transportation
and tex'"
tile industries, as well as waterworks, accelerated the development of
more sophisticated
valves. With the obvious temperature
considera-
tions of steam service, valves could no longer be made of wood or soft
metals. Instead,
steam engineering
led to iron valves, machined
to
close tolerances. Not only were these iron valves far more durable,
they were able to withstand
the high temperatures
and excessive
stroking associated with steam engines without excessive leaking.
The advent of steam power produced a greater need for coal, which
led to the development
of sophisticated
underground
pumping
sys-
tems, including new types and styles of valves, such as gate valves.
The Industrial Age also spurred the use of natural gas in cities as the
fuel for lighting and heating, which required simple ball valves for this
early gaseous application.
The Corliss steam engine (Fig. 1.2), unveiled in 1876, wa. designed
with sophisticated self-acting control valves-including
the fir.t intro-
duction of linear globe valves, some of which are similar to designs
available today.
The discovery of crude oil as a plentiful and inexpen.ive
form of
power in the early nineteenth
century spawned
the creation bf the
petroleum refinery. From refineries, other process indu.trill
.oon fol-
lowed, which led to the development of chemical, petrochemical, pulp
and paper, and food and beverage
processing
plants-creating
the
need for hundreds of process valves in each plant.
Electricity as a source of power led to the creation of coal-fired,
hydroelectric, and, eventually, nuclear power plants, which Involved

the use of valves in not only simple water and steam applications but
also severe service applications that involved high pressure drops and
subsequent cavitation, flashing, and choking.

1.2.3
The Valve and the Modern Era

Before the 1930s, nearly all valves in process plants were manually
operated, which required workers to open and close the valves by hand
according to the needs of the process. Obviously, this resulted in a slow
response, since a worker had to run or pedal a bicycle from the control
room to the valve, as well as poor accuracy in throttling
situations
where a worker had to estimate a certain valve position. For those rea-
sons, during that decade, automated
control valves made their first
appearance. Control valves allowed the control room to send pneumat-
ic signals directly to the valve, which then moved to the necessary posi-
tion automatically, without the need of human involvement.
Today, the global valve industry involves hundreds of global manu-
facturers who produce thousands
of designs of manual, check, pres-
sure-relief, and control valves. Modern valve designs range from sim-
ple gate valves, similar in function to those used by early Egyptian

farmers, to control valves equipped with microprocessors for single-
loop control.
According
to the Valve Manufacturers
Association
(VMA), valve manufacturing in 1993 was a US$2.7billion industry. As
shown in Figs. 1.3 and 1.4, control valves are the fastest growing seg-
ment of the valve industry, indicating the quickening pace of automa-
tion in process industry.

Introduction
to Valves
7

1.3
Valve Classification
According to Function
1.3.1
Introduction to Function
Classifications

By the nature of their design and function in handling process fluids,
valves can be categorized into three areas: on-off
valves, which handle
the function of blocking the flow or allowing it to pass; non return
valves, which only allow flow to travel in one direction; and throttling
valves, which allow for regulation
of the flow at any point between
fully open to fully closed.
One confusing aspect of defining valves by function is that specific
valve-body
designs-such
as globe, gate, plug, ball, butterfly, and
pinch styles-may
fit into one, two, or all three classifications.
For
example, a plug valve may be used for on-off service, or with the
addition
of actuation,
may be used as a throttling
control valve.
Another example is the globe-style body, which, depending
on its
internal
design, may be an on-off, nonreturn,
or throttling
valve.
Therefore,
the user should be careful when equating
a particular
valve-body style with a particular classification.

1.3.2
On-off Valves

Sometimes referred to as block valves, on-off valves are used to start or
stop the flow of the medium through the process. Common on-off
valves include gate, plug, ball, pressure-relief, and tank-bottom valves
(Fig. 1.5).A majority of on-off valves are hand-operated, although they
can be automated with the addition of an actuator (Fig. 1.6).
On-off valves are commonly used in applications
where the flow
must be diverted around an area in which maintenance is being per-
formed or where workers must be protected from potential safety haz-
ards. They are also helpful in mixing applications where a number of
fluids are combined for a predetermined
amount of time and when
exact measurements are not required. Safety management systems also
require automated on-off valves to immediately shut off the system
when an emergency situation occurs.
Pressure-relief valves are self-actuated on-off valves that open only
when a preset pressure is surpassed (Fig. 1.7). Such valves are divided
into two families: relief valves and safety valves. Reliefvalves are used to
guard against overpressurization of a liquid service. On the other hand,
safety valves are applied in gas applications where overpressurization of
the system presents a safety or process hazard and must be vented.

1.3.3
Nonreturn Valves

Nonreturn valves allow the fluid to flow only in the desired direction.
The design is such that any flow or pressure in the opposite direction
is mechanically restricted from occurring. All check valves are nonre-
turn valves (Fig. 1.8).
Nonreturn valves are used to prevent backflow of fluid, which could
damage equipment
or upset the process. Such valves are especially
useful in protecting a pump in liquid applications or a compressor in
gas applications from backflow when the pump or compressor is shut
down. Nonreturn valves are also applied in process systems that have
varying pressures, which must be kept separate.

1.3.4
Throttling Valves

Throttling valves are used to regulate the flow, temperature, or pres-
sure of the service. These valves can move to any position within the
stroke of the valve and hold that position, including the full-open or
full-closed positions.
Therefore, they can act as on-off valves also.
Although many throttling
valve designs are provided with a hand-
operated manual handwheel or lever, some are equipped with actua-

tors or actuation systems, which provide greater thrust and position-
ing capability, as well as automatic control (Fig. 1.9).
Pressure regulators are throttling valves that vary the valve's position
to maintain constant pressure downstream
(Fig. 1.10). If the pressure
builds downstream, the regulator closes slightly to decrease the pres-
sure. If the pressure decreases downstream,
the regulator
opens to
build pressure.
As part of the family of throttling valves, automatic
control
valves,
sometimes referred to simply as control
valves,
is a term commonly
used to describe valves that are capable of varying flow conditions to
match the process requirements. To achieve automatic control, these
valves are always equipped with actuators. Actuators are designed to
receive a command signal and convert it into an specific valve position
using an outside
power source (air, electric, or hydraulic),
which
matches the performance needed for that specific moment.

1.3.5
Final Control Elements within
a Control Loop

Control valves are the most commonly used final control element. The
term final
control
element
refers to the high-performance
equipment

Figure 1.9 Globe con-
trol valve with extended
bonnet (left) with quar-
ter-turn
blocking
ball
valves
(right
and bot-
tom) in refining service.
(Courtesy
oj
Valtek
InternationaO

Figure 1.10
Pressure
regulator.
(Courtesy
oj
Valtek InternationaO

11

12
Chapter
One

needed to provide
the power and accuracy
to control the flowing
medium
to the desired
service conditions.
Other control elements
include metering pumps, louvers, dampers, variable-pitch fan blades,
and electric current-control devices.
As a final control element, the control valve is part of the control loop,
which usually
consists of two other elements
besides
the control
valves: the sensing element and the controller. The sensing element (or
sensor) measures a specific process condition, such as the fluid pres-
sure, level, or temperature. The sensing element uses a transmitter to
send a signal with information about the process condition to the con-
troller or a much larger distributive
control system. The controller
receives the input from the sensor and compares it to the set point, or
the desired value needed for that portion of the process. By comparing
the actual input against the set point, the controller can make any
needed corrections to the process by sending a signal to the final con-
trol element, which is most likely a control valve. The valve makes the
change according to the signal from the controller, which is measured
and verified by the sensing element, completing the loop. Figure 1.11
shows a diagram of a common control loop, which links a controller

Introduction
to Valves
13

with the flow (FT), pressure (PT), and temperature
transmitters
(TT)
and a control valve.

1.4
Classification According
to Application

1.4.1
Introduction to Application
Classifications

Although valves are often classified according to function, they are
also grouped according to the application, which often dictates the fea-
tures of the design. Three classifications are used: general service valves,
which describes a versatile valve design that can be used in numerous
applications without modification; special service valves, which are spe-
cially designed
for a specific application;
and severe service valves,
which are highly engineered to avoid the side effects of difficult appli-
cations.

1.4.2
General Service Valves

General service valves are those valves that are designed
for the
majority of commonplace applications
that have lower-pressure
rat-
ings between American National Standards Institute Class 150 and 600
(between PN 16 and PN 100), moderate-temperature
ratings between
-50 and 650°F (between -46 and 343°C), noncorrosive
fluids, and
common pressure drops that do not result in cavitation or flashing.
General service valves have some degree of interchangeability
and
flexibility built into the design to allow them to be used in a wider
range of applications. Their body materials are specified as carbon or
stainless steels. Figure 1.12 shows an example of two general service
valves, one manually operated and the other automated.

1.4.3
Special Service Valves

Special service valves is a term used for custom-engineered
valves that
are designed for a single application
that is outside normal process
applications. Because of its unique design and engineering, it will only
function inside the parameters and service conditions relating to that
particular application. Such valves usually handle a demanding tem-
perature, high pressure, or a corrosive medium. Figure 1.13 shows a
control valve designed with a sweep-style body and ceramic trim to