ANSI ISA 75.05.01 Control Valve Terminology

AMERICAN NATIONAL STANDARD

ANSI/ISA –75.05.01–2000

Control Valve Terminology

Approved 10 January 2001 TM

ISA–The Instrumentation, Systems, and Automation Society COPYRIGHT The Instrumentation, Systems, and Automation Society

ANSI/ISA–75.05.01–2000 Control Valve Terminology ISBN: 1-55617-741-0

Copyright � 2000 by ISA–The Instrumentation, Systems, and Automation Society. All rights reserved. Not for resale. Printed in the United States of America. No part of this publication may b e reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise), without the prior written permission of the Publisher. ISA 67 Alexander Drive P.O. Box 12277 Research Triangle Park, North Carolina 27709 USA

COPYRIGHT The Instrumentation, Systems, and Automation Society

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ANSI/ISA–75.05.01–2000

Preface This preface, as well as all footnotes and annexes, is included for information purposes and is not part of ANSI/ISA–75.05.01–2000. The standards referenced within this document may contain provisions which, through reference in this text, constitute requirements requirements of this document. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this document are encouraged to investigate the possibility of applying the most recent editions of the standards indicated within this document. Members of IEC and ISO maintain registers of currently valid International Standards. ANSI maintain registers of currently valid U.S. National Standards. This document has been prepared as part of the service of ISA–The Instrumentation, Systems, and Automation Society, Society, toward a goal of uniformity in the field of instrumentation. To be of real value, this document should not be static but should be subject to periodic review. Toward this end, the Society welcomes all comments and criticisms and a nd asks that they be addressed to the Secretary S ecretary,, Standards and Practices Board; ISA; 67 Alexander Drive; P. P. O. Box 12277; Research Triangle Park, NC 27709; Telephone (919) 549-8411; 549-8411; Fax (919) 549-8288; E-mail: [email protected]. The ISA Standards and Practices Department is aware of the growing need for attention to the metric system of units in general, and the International System of Units U nits (SI) in particular, in the preparation of instrumentation standards. The Department is further aware of the benefits benefits to USA users of ISA standards of incorporating suitable references to the SI (and the metric system) in their business and professional dealings with other countries. Toward this end, this Department will endeavor to introduce introduce SI-acceptable metric units in all new and revised standards, recommended practices, and technical reports to the greatest extent possible. Standard for Use of the International System of Units (SI): The Modern Metric System , published by the American Society S ociety for Testing Testing & Materials as IEEE/ASTM SI 10-97, and future revisions, will be the reference guide guid e for definitions, symbols, abbreviations, and conversion factors. It is the policy of ISA to encourage and welcome the participation of all concerned individuals and interests in the development of ISA ISA standards, recommended practices, practices, and technical reports. Participation in the ISA standards-making process by an individual in no way constitutes endorsement by the employer of that individual, of ISA, or of any of the standards, recommended practices, and technical reports that ISA develops. CAUTION — ISA ADHERES TO THE POLICY OF THE AMERICAN NATIONAL STANDARDS INSTITUTE WITH REGARD TO PATENTS. IF ISA IS INFORMED OF AN EXISTING PATENT THAT IS REQUIRED FOR USE OF THE STANDARD, IT WILL REQUIRE THE OWNER OF THE PATENT TO EITHER GRANT A ROYALTY-FREE LICENSE FOR USE OF THE PATENT BY USERS COMPLYING WITH THE STANDARD OR A LICENSE ON REASONABLE TERMS AND CONDITIONS THAT ARE FREE FROM UNFAIR DISCRIMINATION. EVEN IF ISA IS UNAWARE OF ANY PATENT COVERING THIS STANDARD, THE USER IS CAUTIONED THAT IMPLEMENTATION OF THE STANDARD MAY REQUIRE USE OF TECHNIQUES, PROCESSES, OR MATERIALS COVERED BY PATENT RIGHTS. ISA TAKES NO POSITION ON THE EXISTENCE OR VALIDITY OF ANY PATENT RIGHTS THAT MAY BE INVOLVED IN IMPLEMENTING THE STANDARD. ISA IS NOT RESPONSIBLE FOR IDENTIFYING ALL PATENTS THAT MAY REQUIRE A LICENSE BEFORE IMPLEMENTATION OF THE STANDARD OR FOR INVESTIGATING THE VALIDITY OR SCOPE OF ANY PATENTS BROUGHT TO ITS ATTENTION. THE USER SHOULD CAREFULLY INVESTIGATE RELEVANT PATENTS BEFORE USING THE STANDARD FOR THE USER’S INTENDED APPLICATION.


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HOWEVER, ISA ASKS THAT ANYONE REVIEWING THIS STANDARD WHO IS AWARE OF ANY PATENTS THAT MAY IMPACT IMPLEMENTATION OF THE STANDARD NOTIFY THE ISA STANDARDS AND PRACTICES DEPARTMENT OF THE PATENT AND ITS OWNER. ADDITIONALLY, THE USE OF THIS STANDARD MAY INVOLVE HAZARDOUS MATERIALS, OPERATIONS OR EQUIPMENT. THE STANDARD CANNOT ANTICIPATE ALL POSSIBLE APPLICATIONS OR ADDRESS ALL POSSIBLE SAFETY ISSUES ASSOCIATED WITH USE IN HAZARDOUS CONDITIONS. THE USER OF THIS STANDARD MUST EXERCISE SOUND PROFESSIONAL JUDGMENT CONCERNING ITS USE AND APPLICABILITY UNDER THE USER’S PARTICULAR CIRCUMSTANCES. THE USER MUST ALSO CONSIDER THE APPLICABILITY OF ANY GOVERNMENTAL REGULATORY LIMITATIONS AND ESTABLISHED SAFETY AND HEALTH PRACTICES BEFORE IMPLEMENTING THIS STANDARD. The following people served as members of ISA Subcommittee SP75.05: NAME

COMPANY

J. Reed, Chairman W. Weidman, Managing Director T. Abromaitis G. Barb H. Baumann H. Boger J. Brett* R. Brodin D. Buchanan, F. Cain C. Corson M. Glavin F. Harthun C. Koloboff G. Kovecses G. Richards K. Schoonover* L. Stratton F. Sullivan R. Terhune

Norriseal Parsons Energy and Chemicals Group, Inc. Red Valve Company, Inc. Consultant H B Services Partners LLC Masoneilan/Dresser Con-Tek Valves, Inc. Fisher Controls International, Inc. Union Carbide Corporation Flowserve-FCD Fluor Daniel, Inc. Grinnell Corporation Consultant Consultant Yarway Company Richards Industries, Inc. Con-Tek Valves, Inc. Control Components, Inc. Consultant Consultant

The following people served as members of ISA Committee SP75: NAME

COMPANY

D. Buchanan, Chairman W. Weidman, Managing Director A. Abromaitis H. Backinger G. Barb H. Baumann H. Boger G. Borden

Union Carbide Corporation Parsons Energy & Chemicals Group Red Valve Company, Inc. J. F. Kraus & Company Retired H B Services Partners LLC Masoneilan Dresser Consultant

______ * One vote per company.


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S. Boyle R. Brodin F. Cain C. Corson M. Coughran A. Engels H. Fuller J. George A. Glenn L. Griffith B. Guinon F. Harthun B. Hatton J. Jamison R. Jeanes J. Kersh C. Langford A. Libke R. Louviere O. Lovett A. McCauley R. McEver H. Miller T. Molloy L. Ormanoski J. Ozol W. Rahmeyer J. Reed K. Schoonover A. Shea E. Skovgaard H. Sonderegger R. Terhune

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Neles Automation Fisher Controls International, Inc. Flowserve Corporation Fluor Daniel Inc. Fisher Controls Praxair, Inc. Valvcon Corporation Richards Industries Flowserve Corp. Consultant/Retired Shell Chemical Retired DeZurik Division Unit Bantrel, Inc. TXU Electric M. W. Kellogg Company Cullen G. Langford, Inc. DeZurik Valve Company Creole Engineering Sales Company Consultant/Retired Chagrin Valley Controls, Inc. Bettis Corporation Control Components, Inc. CMES Inc. Frick Company Commonwealth Edison Utah State University Norriseal Con-Tek Valves, Inc. Copes-Vulcan, Inc. Leslie Controls, Inc. Tyco Flow Control Retired

This published standard was approved for publication by the ISA Standards and Practices Board on 30 December 2000. NAME

COMPANY

M. Zielinski D. Bishop P. Brett M. Cohen M. Coppler B. Dumortier W. Holland A. Iverson R. Jones V. Maggioli

Fisher-Rosemount Systems, Inc. Consultant Honeywell, Inc. Senior Flexonics, Inc. Ametek, Inc. Schneider Electric SA Southern Company Ivy Optiks Dow Chemical Co. Feltronics Corp.

______ * One vote per company.


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T. McAvinew A. McCauley, Jr. G. McFarland D. Rapley R. Reimer J. Rennie H. Sasajima R. Webb W. Weidman J. Weiss J. Whetstone M. Widmeyer R. Wiegle C. Williams G. Wood

Bateman Engineering, Inc. Chagrin Valley Controls, Inc. Westinghouse Process Control Inc. Rapley Consulting Inc. Rockwell Automation Factory Mutual Research Corp. Yamatake Corp. Altran Corp. Parsons Energy & Chemicals Group EPRI National Institute of Standards & Technology EG&G Defense Materials CANUS Corp. Eastman Kodak Co. Graeme Wood Consulting


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ANSI/ISA–75.05.01–2000

Contents 1 Scope ............................................................................................................................................... 9 2 Purpose ............................................................................................................................................ 9 3 Definitions......................................................................................................................................... 9


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1

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Scope

This standard contains terminology for control valves.

2

Purpose

To provide a glossary of definitions commonly used in the control valve industry.

3

Definitions

3.1 Accuracy: the degree of conformity of an indicated value to a recognized accepted standard value or ideal value. 3.2 Accessories: devices usually attached to the actuator for various control functions such as positioners, relays, solenoid valves, airsets, handwheel, and limit switches. 3.3 Actuator: a pneumatic, hydraulic, or electrically powered device which supplies force and motion to position a valve’s closure member at or between the open or closed position. 3.3.1 Bellows actuator: a fluid powered device in which the fluid acts upon a flexible convoluted component, the bellows. 3.3.2 Diaphragm actuator: a fluid powered device in which the fluid acts upon a flexible component, the diaphragm. (See figure 1.) 3.3.3 Double-acting actuator: a device in which power is supplied in either direction. (See figure 2.) 3.3.4 Electrohydraulic actuator: a device that converts electrical energy to hydraulic pressure and into motion. 3.3.5 Electromechanical actuator: a device that converts electrical energy into motion. 3.3.6 Hydraulic actuator: a fluid device which converts the energy of an incompressible fluid into motion. 3.3.7 Piston actuator: a fluid powered device in which the fluid acts upon a movable piston to provide motion to the actuator stem. (See figure 2.)


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Figure 1 – Single-acting diaphragm actuators 3.3.8 Pneumatic actuator: a device that converts the energy of a compressible fluid, usually air, into motion. 3.3.9 Single-acting actuator: a device in which the power supply acts in only one direction, e.g., a spring diaphragm actuator or a spring return piston actuator. (See figures 1 and 2.) 3.3.10 Vane actuator: a fluid powered device in which the fluid acts upon a pivoted member, the vane, to provide rotary motion.


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Figure 2 – Piston actuators 3.4 Actuator stem or actuator shaft: the part that connects the actuator to the valve stem or shaft and transmits motion (force) from the actuator to the valve. Rotary motion valves have shafts while linear motion valves generally have stems. 3.5 Actuator effective area: the net area of piston, bellows, vane or diaphragm acted on by fluid pressure to generate actuator output force. 3.6 Air set: a regulator that is used to control the supply pressure to the valve actuator and its auxiliaries. 3.7 Angle valve: a valve design in which one port is colinear with the valve stem or actuator, and the other port is at a right angle to the valve stem. (See figure 3.)


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Figure 3 – Angle valve 3.8 Back face: the machined surface on the side of a through-bolted flange, opposite the gasket face, that is provided for nut seating. 3.9 Back seat: a seating surface in the bonnet that mates with the closure member or valve stem in the extreme open position to provide pressure isolation of the stem seal. 3.10 Ball: a spherically shaped closure member. 3.10.1 Full ball: a closure member that has a complete spherical surface with a flow passage through it. 3.10.2 Segmented ball: a closure member that is a segment of a spherical surface which may have one edge contoured to yield a desired flow characteristic. 3.11 Ball valve: a valve with a rotary motion closure member consisting of a full ball or a segmented ball. 3.12 Bellows stem seal: a thin wall, convoluted, flexible component that makes a hermetic seal between the stem and bonnet or body and allows stem motion. 3.13 Bench set: the shop calibration of the actuator spring range of a control valve, to account for the in-service process forces.


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3.14 Body: the main pressure boundary of the valve that also provides the pipe connecting ends, the fluid flow passageway, and supports the valve trim. 3.14.1 Encapsulated body: all surfaces of the body are covered by a continuous surface layer of a different material, usually an elastomeric or polymeric material. 3.14.2 Globe body: a valve body distinguished by a globular shaped cavity around the port region, wherein the closure member motion is linear and normal to the plane of the port. (See figure 4A.) 3.14.3 Lugged body: a thin annular section body with lug protrusions on the outside diameter of the body, whose end surfaces mount between the pipeline flanges or may be attached to the end of a pipeline without any additional flange or retaining parts, using either through-bolting and/or tapped holes. 3.14.4 Pinch Body: a body containing a flexible elastomeric tubular member which can be mechanically squeezed. (See figure 8.) 3.14.5 Split body: a valve body design in which the seat and gaskets are secured between two segments of a valve body. (See figure 4B.) 3.14.6 Wafer body: a thin annular section butterfly body whose end surfaces are located and clamped between the piping flanges by bolts extending from flange to flange.

Figure 4 – Guided valve bodies


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Figure 5 – Diaphragm valve 3.14.7 Weir-type body: a body having a raised contour contacted by a diaphragm to shut off fluid flow. Also referred as a Saunders Patent Diaphragm Valve. (See figure 5.) 3.15 Body cavity: the internal chamber of the valve body. 3.16 Bonnet: the portion of the valve that contains the packing box and stem seal and may guide the stem. It provides the principal opening to the body cavity for assembly of internal parts or it may be an integral part of the valve body. It may also provide for the attachment of the actuator to the valve body. Typical bonnets are bolted, threaded, welded, pressure-sealed, or integral with the body. 3.17 Bonnet bolting: a means of fastening the bonnet to the body. It may consist of studs with nuts for a flanged bonnet joint, studs threaded into the bonnet neck of the body, or bolts through the bonnet flange. 3.18 Bonnet gasket: a deformable seal between the mating surfaces of the body and bonnet. It may be deformed by bonnet bolting loading or energized by fluid pressure within the valve. 3.19 Bonnet, seal welded: a bonnet welded to a body to provide a zero leakage joint. 3.20 Booster relay: a volume or pressure amplifying pneumatic relay that is used to reduce the time lag in pneumatic circuits by reproducing pneumatic signals with high volume and/or high pressure output. 3.21 Boss: a localized projection on a valve or actuator surface provided for various purposes, such as drain connections, auxiliary connections, yoke connection or other attachments.


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3.22 Bottom flange: a part that closes a valve body opening opposite the bonnet opening. It may include a guide bushing and/ or serve to allow reversal of the valve action. In three-way valves, it may provide the lower flow connection and its seat. 3.23 Bubble tight: a nonstandard term used to refer to control valve seat leakage. Refer to ANSI/FCI 70-2 for specification of seat leakage classifications. 3.24 Bushing: a device which supports and/or guides moving parts such as valve stems or shafts. 3.25 Butterfly valve: a valve with a circular body and a rotary motion disk closure member, pivotally supported by its shaft. (See figure 6.)

Figure 6 – Butterfly valve 3.26 Cage: a part of a valve trim, in a globe or angle body, that surrounds the closure member and whose flow passages may provide flow characterization and/or a seating surface. It may also provide stability, guiding, balance, and alignment, and facilitate assembly of other parts of the valve trim. 3.27 Calibration cycle: the application of known values of the measured variable and the recording of corresponding values of the output readings, over the range of the valve in both ascending and descending directions. See ANSI/ISAS51.1-1979 (R1993), Process Instrumentation Terminology. 3.28 Capacity: the rate of flow through a valve usually stated in terms of C V or KV. 3.29 Cavitation: a two-stage phenomenon of liquid flow. The first stage is the formation of vapor bubbles within the liquid system due to static pressure of fluid falling below the fluid vapor pressure; the second stage is the collapse or implosion of these cavities back into an all-liquid state as the fluid decelerates and static pressure is recovered.


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3.30 Characterized cam: a component in a valve positioner used to relate the closure member position to the control signal. 3.31 Characterized trim: control valve trim that provides defined flow characteristics, such as equal percentage, linear or quick opening, usually stated in terms of C V or KV versus travel. 3.32 Choked flow: a condition wherein the flow rate through a restriction does not increase when the downstream pressure is decreased at a fixed inlet pressure. 3.33 Class: a convenient round number used to designate allowable pressure/temperature ratings for valves and pipe fittings using arbritrary Class numbers from tables developed by A SME and ISO for a variety of materials. 3.34 Clearance flow: that flow below the minimum controllable flow with the closure member not seated. 3.35 Closure member: the movable part of the valve that is positioned in the flow path to modulate the rate of flow through the valve. 3.36 Closure member configurations: 3.36.1 Characterized: closure member with contoured surface, such as the "Vee Plug," to provide desired flow characteristics. 3.36.2 Cylindrical: a cylindrical closure member with a flow passage through it (or a partial cylinder). 3.36.3 Eccentric rotary plug: closure member face of a rotary motion valve that is not concentric with the shaft centerline and moves into seat when closing. 3.36.4 Eccentric spherical disk: the disk is a spherical segment in a rotary motion valve that is not concentric with the disk shaft and moves into the seat when closing. 3.36.5 Linear: a closure member that moves in a line perpendicular to the seating plane. 3.36.6 Rotary: a closure member that is rotated into or away from a seat to modulate flow. 3.36.7 Tapered: closure member is tapered and may be lifted from seating surface before rotating to close or open. 3.37 Cold working pressure: the maximum pressure rating of a valve or fitting coincident with ambient temperature, generally in the range from -29º C to +38º C (-20º F to +100º F).


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3.38 Compressor: the device, in a weir-type or sleeve (pinch) valve, that the valve stem forces against the backside of the diaphragm or sleeve to cause the diaphragm or sleeve to move and seal against the internal flow passageway of the valve body. 3.39 Control signal override device: a device that overrides the control signal to the valve actuator, e.g., solenoid valves, lock-up valves, bypass valves, etc. 3.40 Control valve: a power actuated device which modifies the fluid flow rate in a process control system. It consists of a valve connected to an actuator mechanism (including all related accessories) that is capable of changing the position of a closure member in the valve in response to a signal from the controlling system. 3.41 Control valve gain: the change in the flow rate as a function of the change in valve travel. It is the slope of the installed flow characteristic curve. 3.42 Cracked flow: a nonstandard term. See "Clearance flow." 3.43 Cycling life: a number of cycles over which a device will operate without changing its performance beyond tolerance. 3.44 CWP: see “Cold working pressure”. 3.45 Dashpot: a less preferred term. See "Snubber." 3.46 Data plate: a less preferred term. See "Nameplate." 3.47 Dead band, Control valve: the range through which a control valve’s input signal may be varied, upon reversal of direction, without initiating an observable change in the position of the closure member. 3.48 Dead end shut off: a nonstandard term used to refer to control valve leakage. Refer to ANSI/FCI 70-2 for specification of leakage classifications. 3.49 Diaphragm valve: see "Body: weir type body." 3.50 Direct acting valve: a valve that travels to the closed position when the signal increases. 3.51 Disk: a circular shaped closure member used to modify the flow rate with either linear or rotary motion.


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3.52 Disk valve: a valve with a closure member consisting of a disk that moves with a rotary or linear motion against a stationary disk, each disk having flow passages through it. 3.53 Downstream seating: seating assisted by pressure differential across the closure member in the closed position, moving the closure member slightly downstream into tighter contact with the seat ring seal that is supported by the body. 3.54 Drift: an undesired change in the output/input relationship over a period of time. 3.55 Drip tight: a nonstandard term used to refer to control valve leakage. Refer to ANSI/FCI 70-2 for specification of leakage classifications. 3.56 Drop tight: a nonstandard term used to refer to control valve leakage. Refer to ANSI/FCI 70-2 for specification of leakage classifications. 3.57 Dual sealing valve: a valve that uses a resilient seating material for the primary seal and a metal-to-metal seat for a secondary seal. 3.58 Dynamic unbalance: the net force/torque produced on the valve stem/shaft by fluid pressure acting on the closure member and stem/shaft at stated travel and flowing conditions. 3.59 End connection: the configuration provided to make a connection with the pipe. 3.59.1 Flanged: valve end connections incorporating flanges that mate with corresponding flanges on the piping. 3.59.2 Split clamp: valve end connections of various proprietary designs using split clamps to apply gasket or mating surface loading. 3.59.3 Threaded: valve end connections incorporating threads, either male or female. 3.59.4 Welded: valve end connections which have been prepared for welding to the line pipe or other fittings. May be butt weld (BWE), or socket weld (SWE). 3.60 End-to-end dimension: a nonstandard control valve term. See "Face-to-face dimension." 3.61 Environment: ambient conditions (including temperature, pressure, humidity, radioactivity and corrosiveness of the atmosphere) surrounding the valve and actuator. Also, the mechanical and seismic vibration transmitted through the piping or heat radiated toward the actuator from the valve body.


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3.62 Erosion-resistant trim: valve trim that has been designed with special surface materials or geometry to resist the erosive effects of the fluid flow. 3.63 Extension bonnet: a bonnet with a packing box that is extended above the usual height so to maintain the temperature of the packing within its operating limits. 3.64 Face-to-face dimension: the dimension from the face of the inlet opening to the face of the outlet opening of a valve. 3.65 Flange facing: the finish on the end connection that mates with gasket surfaces. 3.66 Failure mode: the position to which the valve closure member moves when the actuating energy source fails. 3.66.1 Fail-closed: a condition wherein the valve closure member moves to a closed position when the actuating energy source fails. 3.66.2 Fail-in-place: a condition wherein the valve closure member stays in its last position when the actuating energy source fails. 3.66.3 Fail-open: a condition wherein the valve closure member moves to an open position when the actuating energy source fails. 3.66.4 Fail-safe: a characteristic of a particular valve and its actuator, which upon loss of actuating energy supply, will cause a valve closure member to be fully closed, fully open or remain in the last position, whichever position is defined as necessary to protect the process. Fail-safe action may involve the use of auxiliary controls connected to the actuator. 3.67 Flangeless control valve: a valve without integral line flanges, which is installed by bolting b etween companion flanges, with a set of bolts, or studs, generally extending through the companion flanges. 3.68 Flow characteristic: an indefinite term. (See below "Inherent flow" and " Installed flow.") 3.68.1 Equal percentage characteristic: an inherent flow characteristic which, for equal increments of rated travel, will ideally give equal percentage changes of the flow coefficient (C v or Kv). 3.68.2 Inherent flow characteristic: the relationship between the flow rate and the closure member travel as it is moved from the closed position to rated travel with constant pressure drop across the valve.


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3.68.3 Installed flow characteristic: the relationship between the flow rate and the closure member travel as it is moved from the closed position to rated travel as the pressure drop across the valve is influenced by the varying process conditions. 3.68.4 Linear characteristic: an inherent flow characteristic that can be represented by a straight line on a rectangular plot of flow coefficient (Cv or Kv) versus rated travel. Therefore, equal increments of travel provide equal increments of flow coefficient (C v or Kv). 3.68.5 Modified parabolic characteristic: an inherent flow characteristic which provides equal percent characteristic at low closure member travel and approximately a linear characteristic for upper portions of closure member travel. 3.68.6 Quick opening characteristic: an inherent flow characteristic in which a maximum flow coefficient is achie ved with minimal closure member travel. 3.69 Flow coefficient (CV & KV): a constant related to the geometry of a valve, for a given valve travel, that establishes flow capacity. 3.70 Globe valve: a valve with a linear motion closure member whose seal is perpendicular to the stem motion, one or more ports and a body distinguished by a globular shaped cavity around the port region. (See figure 4a.) 3.71 Guides, closure member: the means by which the closure member is aligned with the seat and held stable throughout its travel. The guide is held rigidly in the body, bonnet, and/or bottom flange. 3.72 Hand jack: a manual hydraulic or mechanical override device, u sing a lever, to stroke a valve or to limit its travel. 3.73 Handwheel: a mechanical manual override device, using a rotary wheel, to stroke a valve or to limit its travel. 3.74 Hard facing: a material applied to valve internals to resist fluid erosion and/or to reduce the chance of galling between moving parts, particularly at high temperatures. 3.75 Hard plating: a thin metal deposit, sometimes electroplated, used to provide a surface coating. Hard plating is many orders of magnitude thinner than hard facing. 3.76 Hysteresis: the maximum difference in output value for any single input value during a calibration cycle, excluding errors due to dead band. This difference is sometimes called hysteretic error. See ANSI/ISA-S51.1-1979 (R1993), Process Instrumentation Terminology. 3.77 Hysteresis plus dead band: the maximum difference for the same input between the upscale and downscale output values during a full range traverse in each direction. This is the summation of hysteresis and dead band.


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3.78 Identification plate: a less preferred term. See "Nameplate." 3.79 In-line valve: a valve having a closure member that moves to seat axially in the direction of the flow path. In-line valves are normally operated by a fluid energy source but may be operated mechanically. 3.80 Integral seat: a flow control orifice and seat that is an integral part of the body. 3.81 Integral stem/shaft: a design in which the stem/shaft is an integral part of the closure member. 3.82 Jacketed valve: a valve body cast with a double wall or provided with a double wall by welding material around the body so as to form a passage for a heating or cooling medium. Also refers to valves that are enclosed in split metal jackets having internal heat passageways or electric heaters. Also referred to as "steam jacketed" or "vacuum jacketed." In a vacuum-jacketed valve, a vacuum is created in the space between the body and secondary outer wall to reduce the transfer of heat by convection from the atmosphere to the internal process fluid, usually cryogenic. 3.83 Lantern ring: a rigid spacer assembled in the packing box with packing normally above and below it and designed to allow lubrication of the packing or access for a leak-off connection. 3.84 Lapping: a process of mating contact surfaces by grinding and/or polishing. 3.85 Leakage class: classifications established by ANSI/FCI 70-2 to categorize seat leakage allowances for different needs of seat tightness. 3.86 Leak-off gland: a packing box with packing above and below the lantern ring so as to provide a collection point for fluid leaking past the primary seal (lower packing). 3.87 Lift: a nonstandard term. See "Travel." 3.88 Limit switch: a nonstandard term. See "Position switch." 3.89 Linearity: the closeness to which a curve relating to two variables approximates a straight li ne. 3.90 Lined valve body: a valve body in which a coating or liner has been applied to internal surfaces for corrosion/erosion protection or for flow shutoff. 3.91 Liquid pressure recovery factor (FL) : the square root of the ratio of the actual pressure differential across the valve to the pressure differential to the vena contracta under nonvaporizing conditions without attached fittings. It is used to predict choked


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flow of liquids. See ISA-S75.01-1985 (R1995), Flow Equations for Sizing Control Valves and ANSI/ISA-S75.02-1996, Control Valve Capacity Test Procedures. 3.92 Live loading: a type of sealing system which incorporates a spring element capable of providing a sufficient load over a range of motion to compensate for thermal expansion, wear or consolidation of packing or gaskets. (See figure 7.)

Figure 7 – Live loaded packing 3.93 Lubricator isolating valve: a manually operated valve used to isolate the packing lubricator assembly from the packing box. 3.94 Lubricator packing box: a packing arrangement consisting of a lantern ring with packing rings above and below with provision to lubricate the packing. 3.95 Manual override: see "Hand Jack" and/or "Handwheel." 3.96 Mechanical limit stop: a mechanical device to limit the valve stem travel. 3.97 Modulation: the action of a control valve to regulate fluid flow by varying the position of the closure member. 3.98 Mounting position: the location and orientation of an actuator or auxiliary component relative to the control valve. This can apply to the control valve itself relative to the piping.


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3.99 Multiple orifice: a style of valve trim where the flow passes through a multiple of orifices in parallel or in series. 3.100 Nameplate: a plate attached to a control valve bearing the name of the manufacturer and a listing of valve specifications. 3.101 Needle valve: a type of valve having a needle style plug. 3.102 Nominal size: a numerical designation of size which is common to all components in a piping system other than components designated by outside diameters or by thread size. It is a convenient round number for reference purposes and is only loosely related to manufacturing dimensions. ISO uses initials DN as an abbreviation for the term with the letters DN followed by a numerical value designating size. All equipment of the same nominal size and nominal pressure rating shall have the same mating dimensions appropriate to the type of end connections. 3.103 Nominal pressure: a numerical designation relating to pressure that is a convenient round number for reference purposes. The International Organization for Standardization (ISO) uses the term "nominal pressure" the same way that ANSI uses the term "class" in identifying piping component pressure rating. ISO uses the initials PN as an abbreviation for the term with the letters PN followed by a numerical value designating pressure rating. All equipment of the same nominal diameter and nominal pressure rating shall have the same mating dimensions appropriate to the type of end connections. 3.104 Normally closed valve: see "Fail-close." 3.105 Normally open valve: see "Fail-open." 3.106 Packing: a sealing system consisting of deformable material contained in a packing box which usually has an adjustable compression means to obtain or maintain an effective seal. 3.107 Packing box: the chamber, in the bonnet, surrounding the stem and containing packing and other stem sealing and guiding parts. 3.108 Packing box, purged: a packing arrangement consisting of a lantern ring inside the packing rings to permit introduction of a purge fluid. 3.109 Packing flange: a device that transfers the deforming mechanical load to the packing follower. A packing flange is fastened by studs. 3.110 Packing follower: a part which transfers the deforming mechanical load to the packing from the packing flange or nut.


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3.111 Packing gland: a nonstandard term. See "Packing follower." 3.112 Packing leakage: the quantity of process fluid that escapes through the valve packing. 3.113 Packing lubricator assembly: a device for injection of lubricant/sealer into a lubricator packing box. 3.114 Packing nut: a packing nut is threaded into the packing box transmitting the deforming mechanical load to the packing. 3.115 Pinch or clamp valve: a valve consisting of a flexible elastomeric tubular member where flow control and shutoff is accomplished by mechanically squeezing the flexible member. (See figure 8.)

Figure 8 – Pinch valve 3.116 Piston ring seal: a seal ring installed in a groove on a piston or closure member circumference to minimize the clearance flow between the piston outer diameter and the cylinder bore. 3.117 Plug: a term frequently used to refer to the closure member.


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3.118 Plug configurations: see "Closure member configurations." 3.119 Plug valve: a rotary motion valve with a closure member that may be cylindrical or conical. 3.120 Port: (1) The flow control orifice of a control valve, and (2) the opening of a val ve’s inlet or outlet passageways. 3.121 Port guiding: a valve closure member with wings, or a skirt, fitting into the seat ring bore. 3.122 Positioner: a position controller, which is mechanically connected to a moving part of a final control element or its actuator, and automatically adjusts its output to the actuator in order to maintain a desired position of the closure member in proportion to the input signal. 3.122.1 Double acting: a positioner with two outputs, suited to a double-acting actuator. 3.122.2 Single acting: a positioner with one output, suited to a spring-opposed actuator. 3.123 Position indicator: see "Travel indicator." 3.124 Position switch: a position switch is a pneumatic, hydraulic or electrical device which relates to the valve stem to detect a single, preset valve stem position. 3.125 Position transmitter: the position transmitter is a device that is mechanically connected to the val ve stem or shaft and generates and transmits a pneumatic or electrical signal representing the valve position. 3.126 Post guiding: a design using guide bushing or bushings fitted into the body, bonnet and/or bottom flange to guide the plug’s post. 3.127 Precision: a nonstandard term. See "Repeatability." 3.128 Pressure energized seal: a seal energized by differential pressure. 3.129 Rangeability: the ratio of the largest flow coefficient (C v or Kv) to the smallest controllable flow coefficient (C v or Kv) within which the deviation from the specified flow characteristic does not exceed the stated limits. 3.130 Rated flow coefficient: the flow coefficient (C v or Kv) of the valve at rated travel.


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3.131 Rated travel: the amount of movement of the valve closure member from the closed position to the rated position. 3.132 Relative flow coefficient: the ratio of the flow coefficient (C v or Kv) at given travel to the rated flow coefficient (C v or Kv). 3.133 Relative travel: the ratio of travel at a given travel to the rated travel. 3.134 Repeatability: the closeness of agreement among a number of consecutive measurements of the ou tput for the same value of input under the same operating conditions, approaching from the same direction, for full range traverses. It does not include hysteresis. 3.135 Reproducibility: the closeness of agreement among repeated measurements of the output for the same value o f input made under the same operating conditions over a period of time, approaching from both directions. It includes hysteresis, dead band, drift and repeatability. 3.136 Resolution: the least interval between two adjacent discrete details which can be distinguished one from the other. 3.137 Reverse acting valve: a valve that travels to the open position when the signal increases. 3.138 Screwed ends: a nonstandard term. See “End connections, threaded.” 3.139 Seating surface: the line of contact between the closure member and its mating surface which establishes valve shutoff. 3.140 Seat angle: the angle between the axis of the seat orifice and the seating surface. 3.141 Seat leakage: the quantity of fluid passing through a valve when the valve is in the fully closed position with a pressure differential across the trim. Refer to ANSI/FCI 70-2 for specification of leakage classifications. 3.142 Seat load: the net contact force between the closure member and seat. 3.143 Seat ring: a part of the valve body assembly that provides a seating surface for the closure member and may provide part of the flow control orifice. 3.144 Seat, spring-loaded: a seat utilizing a spring that exerts a force at the point of closure member contact to improve the sealing characteristics. 3.145 Sensitivity: the ratio of the change in output magnitude to the change of the input which causes it, after steady-state has been reached.


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3.146 Shaft: the mechanical member used to support and move a rotary closure member. 3.147 Shaft bearings: devices used in rotary valves to support the shaft and guide the closure member through its travel. 3.148 Sliding disk: a flat or wedge-shaped sliding closure member that modifies flow rate with linear motion across the flow path. 3.149 Slip-in liner: an annular shaped liner that makes a slight interference fit with a butterfly body bore and which may be readily forced into position through the body end. May be plain or reinforced. 3.150 Snubber: a device that is used to damp the motion of the valve stem. 3.151 Spot face: a machined annular surface around a bolt hole on the side of a through bolted flange, opposite the gasket face, that is provided for nut seating. 3.152 Spring rate: the force change per unit change in length of a spring. 3.153 Static unbalance: the net force produced on the valve stem by the fluid pressure acting on the closure member and stem with the fluid at rest and with stated pressure conditions. 3.154 Steam-jacketed valve: see "Jacketed valve." 3.155 Stem anti-rotation device: a mechanical means of preventing rotation of the linear actuator stem and/or valve stem. 3.156 Stem boot: a protective device similar to a flexible bellows, used outside the bonnet to protect the valve stem from the surrounding atmosphere. 3.157 Stem connector: the device that connects the actuator stem to the valve stem. 3.158 Stem guide: a guide bushing closely fitted to the valve stem and aligned with the seat. 3.159 Stem rotation: a phenomenon that occurs in linear motion valves when the hydraulic forces from the process fluid cause the closure member to rotate about the stem axis. 3.160 Stem seals: see "Bellows stem seal" and "Packing."


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3.161 Stroke: a nonstandard term, see "Travel." 3.162 Stroke cycle: a nonstandard term, see "Travel cycle." 3.163 Stroke time: a nonstandard term, see "Travel time." 3.164 Three-way valve: a valve with three end connections, used for combining or diverting flow. (See figure 9.)

Figure 9 – Three way valves 3.165 Throttling: see "Modulating." 3.166 Topworks: a nonstandard term for "Actuator." 3.167 Transducer: a device that is actuated by power from one system and transmits power in another form to a second system, such as a pressure transducer that sends a signal proportional to the measured pressure. 3.168 Travel: the movement of the closure member from the closed position to an intermediate or rated full open position.


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3.169 Travel cycle: travel of the closure member from its closed position to the rated travel opening and its return to the closed position. 3.170 Travel indicator: a pointer and scale used to externally show the position of the closure member; typically in terms of units of opening, percent of travel, or degrees of rotation. 3.171 Travel time: the time required for one-half a travel cycle. 3.172 Trim: the internal components of a valve that modulate the flow of the controlled fluid. 3.172.1 Anti-cavitation trim: a control valve trim style that by its geometry reduces or eliminates the tendency of the controlled liquid to cavitate. 3.172.2 Anti-noise trim: a control valve trim style that by its geometry reduces the noise generated by fluid flowing through the valve. 3.172.3 Balanced trim: control valve trim designed to minimize the net static and dynamic fluid flow forces, from fluid pressure, acting on the trim. 3.172.4 Reduced trim: control valve trim that has a flow area smaller than the full flow area for that valve. 3.172.5 Soft-seated trim: valve trim with an elastomeric, plastic or other readily deformable material used either in the closure member component or seat ring to provide tight shutoff with minimal actuator forces. 3.173 Trunnion: shaft extension(s) on a rotary closure member used to locate and support it with bearings within the valve body. 3.174 Turndown: see "Rangeability." 3.175 Upstream seating: seating assisted by pressure differential across the seat in the closed position, moving the seat into tighter contact with the closure member. 3.176 Vacuum-jacketed valve: see "Jacketed valve." 3.177 Valve: a device used for the control of fluid flow, consisting of a fluid retaining assembly, one or more ports between end openings and a movable closure member which opens, restricts, or closes the port(s).


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3.178 Valve plug: see "Closure member." 3.179 Valve stem: the mechanical member, in a linear motion valve, that connects the actuator stem with the closure member. 3.180 Vena contracta: the portion of a flow stream where fluid velocity is at its maximum and fluid static pressure and the crosssectional area are at their minimum. In a control valve, the vena contracta normally occurs just downstream of the actual physical restriction. 3.181 Yoke: the structure that rigidly connects the actuator power unit to the valve.


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ANSI ISA 75.05.01 Control Valve Terminology

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