-
Air-Operated Valve Evaluation Guide
Effective December 6, 2006, this report has been made publicly
available in accordance with Section 734.3(b)(3) and published in
accordance with Section 734.7 of the U.S. Export Administration
Regulations. As a result of this publication, this report is
subject to only copyright protection and does not require any
license agreement from EPRI. This notice supersedes the export
control restrictions and any proprietary licensed material notices
embedded in the document prior to publication.
-
EPRI 3412 Hillview Avenue, Palo Alto, California 94304 PO Box
10412, Palo Alto, California 94303 USA800.313.3774 650.855.2121
[email protected] www.epri.com
Air-Operated Valve Evaluation Guide
TR-107322
Final Report, May 1999
EPRI Project ManagerJ. Hosler
-
DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIESTHIS
PACKAGE WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS AN
ACCOUNT OF WORKSPONSORED OR COSPONSORED BY THE ELECTRIC POWER
RESEARCH INSTITUTE, INC. (EPRI).NEITHER EPRI, ANY MEMBER OF EPRI,
ANY COSPONSOR, THE ORGANIZATION(S) NAMED BELOW, NORANY PERSON
ACTING ON BEHALF OF ANY OF THEM:
(A) MAKES ANY WARRANTY OR REPRESENTATION WHATSOEVER, EXPRESS OR
IMPLIED, (I) WITHRESPECT TO THE USE OF ANY INFORMATION, APPARATUS,
METHOD, PROCESS, OR SIMILAR ITEMDISCLOSED IN THIS PACKAGE,
INCLUDING MERCHANTABILITY AND FITNESS FOR A PARTICULARPURPOSE, OR
(II) THAT SUCH USE DOES NOT INFRINGE ON OR INTERFERE WITH PRIVATELY
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THAT THIS PACKAGE IS SUITABLETO ANY PARTICULAR USER'S CIRCUMSTANCE;
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(B) ASSUMES RESPONSIBILITY FOR ANY DAMAGES OR OTHER LIABILITY
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DAMAGES) RESULTING FROM YOUR SELECTION OR USE OF THISPACKAGE OR ANY
INFORMATION, APPARATUS, METHOD, PROCESS, OR SIMILAR ITEM DISCLOSED
INTHIS PACKAGE.
ORGANIZATION(S) THAT PREPARED THIS PACKAGEDuke Engineering &
Services, Inc.
ORDERING INFORMATIONRequests for copies of this package should
be directed to the EPRI Distribution Center, 207 Coggins Drive,
P.O. Box23205, Pleasant Hill, CA 94523, (925) 934-4212.Electric
Power Research Institute and EPRI are registered service marks of
the Electric Power Research Institute, Inc.EPRI. POWERING PROGRESS
is a service mark of the Electric Power Research Institute,
Inc.
Copyright 1999 Electric Power Research Institute, Inc. All
rights reserved.
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EPRI Licensed Material
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CITATIONS
This report was prepared by
Duke Engineering and Services, Inc.215 Shuman BoulevardSuite
172Naperville, Illinois 60563
Principal InvestigatorsD. CaronJ. HolstromS. KornL. LutzM.
MurphyS. SwaniganP. Young
MPR Associates, Inc.320 King StreetAlexandria, Virginia
22314-3238
Principal InvestigatorsM. AlbersP. DamerellP. KnittleT.
Walker
This report describes research sponsored by EPRI.
The report is a corporate document that should be cited in the
literature in the followingmanner:
Air-Operated Valve Evaluation Guide: EPRI, Palo Alto, CA: 1999.
TR-107322.
-
vREPORT SUMMARY
Proper engineering evaluation and setup of air-operated valves
is critical to the safeoperation of a nuclear power plant. This
Guide provides an overview of air-operatedvalves and how to
complete an engineering evaluation of them. Also discussed
aremethods for evaluating design basis system conditions, required
thrust or torque, air-actuator output thrust/torque capability, and
operating margin. Guidelines also aregiven for static and dynamic
tests on air-operated valves and for interpreting testresults.
BackgroundIn 1994, EPRI completed the EPRI Motor-Operated Valve
(MOV) PerformancePrediction Program to develop and validate methods
for predicting performance ofmotor-operated valves in nuclear power
plants. Nuclear utilities have applied thesemethods extensively in
response to Nuclear Regulatory Commission Generic Letter 89-10. In
1996, EPRI initiated a pilot program at several nuclear plants to
apply the lessonslearned and methods developed under the MOV
Performance Prediction Programtoward the development and
implementation of plant air-operated valve programs.This Guide
incorporates the lessons learned and methods developed in these
pilotprograms.
ObjectivesTo provide comprehensive guidelines for engineering
evaluations and testing of air-operated valves to demonstrate their
capability to function under design basis flow anddifferential
pressure conditions.
ApproachEPRI teamed with four utilities to develop and implement
technically sound and cost-effective air-operated valve programs.
The process included evaluation of design basissystem conditions
(media, temperature, flow, and differential pressure),
requiredactuation thrusts and torques, air-operator output
thrust/torque capability, and marginfor selected air-operated
valves.
Where applicable, researchers used validated methods developed
under EPRIs MOVprogram to define required thrust/torque. In cases
where such methods were notapplicable, new methods were developed.
Specifically, the EPRI balanced globe valvemodel includes a plug
side loading term that is considered overly conservative for
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vi
many caged globe valve designs. Project researchers applied a
refined balanced globevalve modelwhich explicitly accounts for plug
imbalance area and neglects plug sideloadingfor such valve designs.
In addition, the EPRI unbalanced globe valve model iscurrently
applicable to water flow up to 150F (65.6C). For nominal flow cases
wherefluid temperature was above 150F, researchers applied the EPRI
unbalanced globevalve model as the best available methodology.
Plans call for validation of thesemodeling approaches in 1999.
First-principles-based methods also were developed andapplied for
double-seated and three-way globes, as well as ball valve
designs.
Project researchers developed first-principles methods for
evaluation of air-actuatoroutput thrust/torque capability for
air-actuator designs commonly applied in nuclearservice. They used
these methods, as well as actuator vendor information, to
determineactuator output capability.
ResultsThe EPRI Performance Prediction Methodology (PPM) applied
directly to most air-operated gate and butterfly valves and to
unbalanced globe valves with operatingtemperatures below 150F. The
pilot programs defined a need for additional data todefine friction
coefficients for butterfly valve non-metallic bearings and to
refine andextend the applicability of the EPRI globe valve
methodology.
EPRI PerspectiveThis Guide provides an excellent basis for
developing and implementing a technicallysound air-operated valve
program. It incorporates lessons learned and tools developedunder
the EPRI MOV Performance Prediction Research Program and several
pilot air-operated valve programs.
TR-107322KeywordsValvesAir-operated valves
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ABSTRACT
This guide presents methods for conducting an engineering
evaluation of the designbasis capability of air operated valves in
nuclear power plants. The methods presentedincorporate lessons
learned and tools developed as part of the EPRI Motor OperatedValve
Performance Prediction Research Program and during EPRI pilot AOV
programsimplemented at several nuclear power plants.
The guide includes methods for determining design basis
operating conditions,required thrust/torque, actuator output
capability, and thrust/torque margin for AOVapplications. Guidance
is also provided for static and dynamic testing of AOVs.
The methods are applicable to most rising stem gate and globe
valve designs and one-quarter turn butterfly and ball valves.
Actuator types covered include cylinder,diaphragm, scotch yoke, and
rack and pinion.
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ACKNOWLEDGMENTS
The following individuals and organizations are acknowledged for
their support andguidance in the preparation and review of this
Guide:
Pilot AOV Program Utilities
Alliant /IES UtilitiesMr. Clifford McDonald
Consumers Energy CompanyMr. Robert GambrillMr. Gary Foster
Detroit Edison CompanyMr. A. Nayakwadi
TU Electric CompanyMr. Ben Mays
Additional Technical Reviewers
Mr. Kenneth Beasley, Duke Energy Corporation
Mr. Daryl Bradford, Southern California Edison Company
Mr. Timothy Chan, Tennessee Valley Authority
Mr. Mark Colemen, Public Service Electric and Gas Company
Mr. Kevin Cortis, Northeast Utilities Company
Mr. James Hallenbeck, PECO Energy Company
Mr. Frank Pisarsky, American Electric Power Company
Mr. Robert Poole, Tennessee Valley Authority
Ms. Sonja Waters, Arizona Public Service Company
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CONTENTS
1
INTRODUCTION.............................................................................................................
1-11.1 Purpose and Objective
.................................................................................................
1-11.2 Scope of Evaluation
Guide...........................................................................................
1-21.3 Organization of the Evaluation Guide
...........................................................................
1-2
1.3.1 Overview of AOV Evaluation Methodology (Section 2)
.......................................... 1-31.3.2 Functional
Description and Introduction to Air-Operated Valves (Section 3)
.......... 1-31.3.3 Definition of AOV Functional and Design
Requirements (Section 4) ..................... 1-31.3.4 Determining
Required Thrust or Torque (Section
5).............................................. 1-41.3.5
Evaluation of Valve / Actuator Rated and Survivable Thrust and
Torque(Section
6).......................................................................................................................
1-51.3.6 Evaluation of Air Actuator Output Thrust / Torque
Capability (Section 7) ............... 1-51.3.7 Calculating and
Evaluating Margins (Section
8)..................................................... 1-51.3.8
AOV Testing (Section 9)
........................................................................................
1-51.3.9 References (Section 10)
........................................................................................
1-61.3.10
Appendices..........................................................................................................
1-6
1.4 Basis for
Guide..............................................................................................................
1-6
2 OVERVIEW OF AOV EVALUATION METHODOLOGY
................................................. 2-1
3 FUNCTIONAL DESCRIPTION AND INTRODUCTION TO AIR-OPERATEDVALVES
.................................................................................................................................
3-1
3.1 Valves
...........................................................................................................................
3-13.1.1 Globe Valves (unbalanced, balanced, double seat,
three-way, piloted) ............... 3-2
3.1.1.1 Unbalanced Disc Globe
Valves.......................................................................
3-83.1.1.2 Balanced Disc Globe
Valves...........................................................................
3-93.1.1.3 Double Seat Globe
Valves............................................................................
3-103.1.1.4 Three-Way Globe
Valves..............................................................................
3-113.1.1.5 Balanced Disc Globe Valves With Pilot
......................................................... 3-12
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3.1.2 Gate
Valves.........................................................................................................
3-133.1.3 Butterfly
Valves................................................................................................
3-14
3.1.4 Ball
Valves.........................................................................................................
3-173.1.5 Plug
Valves........................................................................................................
3-20
3.2 Air
Actuators...............................................................................................................
3-213.2.1 Diaphragm, Rising
Stem......................................................................................
3-213.2.2 Diaphragm, Rotating
Stem...................................................................................
3-233.2.3 Piston
..................................................................................................................
3-243.2.4 Rack and Pinion
..................................................................................................
3-253.2.5 Scotch Yoke
........................................................................................................
3-26
3.3
Accessories................................................................................................................
3-263.3.1 Boosters, Accumulators, Solenoid valves
............................................................
3-26
3.3.1.1 Boosters
.......................................................................................................
3-263.3.1.2
Accumulators................................................................................................
3-273.3.1.3 Solenoid Valves
............................................................................................
3-273.3.1.4 Handwheels / Manual Overrides
...................................................................
3-283.3.1.5
Positioners....................................................................................................
3-29
4 DEFINITION OF AOV FUNCTIONAL AND DESIGN
REQUIREMENTS......................... 4-14.1 Valve Structural and
Design Requirements
..................................................................
4-14.2 Actuator Structural and Design
Requirements..............................................................
4-2
4.2.1 Linear Actuators
....................................................................................................
4-24.2.1.1
Diaphragm......................................................................................................
4-24.2.1.2 Piston
.............................................................................................................
4-34.2.1.3 Double Acting
.................................................................................................
4-34.2.1.4 Single Acting (spring
return)............................................................................
4-4
4.2.2 Rotary
Actuators....................................................................................................
4-44.2.3 Controls
.................................................................................................................
4-5
4.2.3.1 Control Voltage Electric Power
Supply............................................................
4-54.2.3.2 Non-safety-Related
AOVs...............................................................................
4-54.2.3.3 Safety-Related
AOVs......................................................................................
4-5
4.3 AOV Capability
Requirements......................................................................................
4-64.3.1 Functional
Requirements.......................................................................................
4-64.3.2 Stroke Time Requirements
....................................................................................
4-74.3.3 Failure
Modes........................................................................................................
4-8
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4.3.4 Determination of Limiting Operating Conditions
..................................................... 4-84.3.5
Allowable Leakage Rate
......................................................................................
4-11
4.3.5.1 Non-safety-Related
AOVs.............................................................................
4-114.3.5.2 Safety-Related
AOVs....................................................................................
4-11
4.4 Air Supply System Requirements
...............................................................................
4-124.5 External Operating
Environment.................................................................................
4-134.6 AOV Orientation
.........................................................................................................
4-144.7 AOV Accessibility
.......................................................................................................
4-154.8 Industry Technical
Issues...........................................................................................
4-16
5 DETERMINING REQUIRED THRUST OR
TORQUE...................................................... 5-15.1
Required Input Information
...........................................................................................
5-15.2 Variables
......................................................................................................................
5-25.3 Definitions
....................................................................................................................
5-75.4 Globe
Valves................................................................................................................
5-8
5.4.1 Unbalanced Disc Globe Valves
.............................................................................
5-95.4.1.1 Total Required Thrust
......................................................................................
5-9
5.4.1.1.1 Opening
Stroke........................................................................................
5-95.4.1.1.2 Closing Stroke
.........................................................................................
5-9
5.4.1.2 Disc and Stem Weight
....................................................................................
5-95.4.1.3 Packing
Load................................................................................................
5-105.4.1.4 Upper Seal Friction Load
..............................................................................
5-105.4.1.5 Stem Rejection Load
....................................................................................
5-105.4.1.6 Disc-to-Body/Cage Friction Load
..................................................................
5-115.4.1.7 DP Load
.......................................................................................................
5-115.4.1.8 Sealing Load (Closing Only)
.........................................................................
5-13
5.4.2 Balanced Disc Globe
Valves................................................................................
5-145.4.2.1 Total Required Thrust
...................................................................................
5-14
5.4.2.1.1 Opening
Stroke......................................................................................
5-145.4.2.1.2 Closing Stroke
.......................................................................................
5-14
5.4.2.2 Disc and Stem Weight
..................................................................................
5-155.4.2.3 Packing
Load................................................................................................
5-155.4.2.4 Upper Seal Friction Load
..............................................................................
5-155.4.2.5 Stem Rejection Load
....................................................................................
5-155.4.2.6 Disc-to-Body/Cage Friction Load
..................................................................
5-16
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5.4.2.7 DP Load
.......................................................................................................
5-175.4.2.8 Sealing Load (Closing Only)
.........................................................................
5-18
5.4.3 Balanced Disc Globe Valves With Pilot
Disc........................................................
5-195.4.3.1 Total Required Thrust
...................................................................................
5-19
5.4.3.1.1 Opening
Stroke......................................................................................
5-195.4.3.1.2 Closing Stroke
.......................................................................................
5-19
5.4.3.2 Disc and Stem Weight
..................................................................................
5-205.4.3.3 Packing
Load................................................................................................
5-205.4.3.4 Upper Seal Friction Load
..............................................................................
5-215.4.3.5 Stem Rejection Load
....................................................................................
5-215.4.3.6 Disc-to-Body/Cage Friction Load
..................................................................
5-215.4.3.7 DP Load
.......................................................................................................
5-215.4.3.8 Sealing Load (Closing Only)
.........................................................................
5-215.4.3.9 Pilot spring force
...........................................................................................
5-22
5.4.4 Double Seat Globe
Valves...................................................................................
5-225.4.4.1 Total Required Thrust
...................................................................................
5-22
5.4.4.1.1 Opening
Stroke......................................................................................
5-225.4.4.1.2 Closing Stroke
.......................................................................................
5-22
5.4.4.2 Disc and Stem Weight
..................................................................................
5-235.4.4.3 Packing
Load................................................................................................
5-235.4.4.4 Upper Seal Friction Load
..............................................................................
5-245.4.4.5 Stem Rejection Load
....................................................................................
5-245.4.4.6 Disc-to-Body/Cage Friction Load
..................................................................
5-255.4.4.7 DP Load
.......................................................................................................
5-255.4.4.8 Sealing Load (Closing Only)
.........................................................................
5-26
5.4.5 Three-Way Globe
Valves.....................................................................................
5-265.4.5.1 Total Required Thrust
...................................................................................
5-265.4.5.1.1 Opening
Stroke..........................................................................................
5-265.4.5.1.2 Closing Stroke
...........................................................................................
5-265.4.5.2 Disc and Stem Weight
..................................................................................
5-275.4.5.3 Packing
Load................................................................................................
5-285.4.5.4 Upper Seal Friction Load
..............................................................................
5-285.4.5.5 Stem Rejection Load
....................................................................................
5-285.4.5.6 Disc-to-Body/Cage Friction Load
..................................................................
5-29
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5.4.5.7 DP Load
.......................................................................................................
5-295.4.5.8 Sealing
Load.................................................................................................
5-30
5.5 Gate Valves
...............................................................................................................
5-305.5.1 Packing
Load.......................................................................................................
5-315.5.2 Sealing Load (Closing Only)
................................................................................
5-315.5.3 Valve Factor
Method............................................................................................
5-325.5.4 Unwedging Load (Opening
Only).........................................................................
5-33
5.6 Butterfly Valves
..........................................................................................................
5-345.6.1 Packing Torque
...................................................................................................
5-35
5.7 Ball Valves
.................................................................................................................
5-355.7.1 Total Required
Torque.........................................................................................
5-35
5.7.1.1
Opening.........................................................................................................
5-355.7.1.2 Closing
..........................................................................................................
5-36
5.7.2 Packing and Static Seat
Torques.........................................................................
5-365.7.3 Dynamic Seat Torque
..........................................................................................
5-375.7.4 Bearing
Torque....................................................................................................
5-375.7.5 Hydrodynamic Torque
.........................................................................................
5-37
5.8 Calculation
Worksheets..............................................................................................
5-38
6 EVALUATION OF VALVE / ACTUATOR RATED AND SURVIVABLE THRUSTAND
TORQUE........................................................................................................................
6-1
6.1 Valve
Limits..................................................................................................................
6-16.2 Actuator Limits
.............................................................................................................
6-2
7 EVALUATION OF AIR ACTUATOR OUTPUT THRUST / TORQUE CAPABILITY
........ 7-17.1 Required Input Information
...........................................................................................
7-17.2 Actuator Output Capability Evaluations
........................................................................
7-2
7.2.1 Overview
...............................................................................................................
7-27.2.1.1 Cylinder Actuators for Rising Stem
Valves.................................................... 7-11
7.2.1.1.1 Double Acting Air Cylinder, Single Ended
.............................................. 7-117.2.1.1.2 Double
Acting Air Cylinder, Double Ended
............................................. 7-137.2.1.1.3 Double
Acting Air Cylinder, Direct Acting (Spring to
Retract).................. 7-157.2.1.1.4 Double Acting Air
Cylinder, Reverse Acting (Spring to Extend) ..............
7-187.2.1.1.5 Single Acting Air Cylinder, Direct Acting (Spring to
Retract) ................... 7-217.2.1.1.6 Single Acting Air
Cylinder, Reverse Acting (Spring to Extend) ...............
7-24
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7.2.1.2 Diaphragm Actuators for Rising Stem Valves
............................................... 7-277.2.1.2.1
Direct Acting Diaphragm (Spring to Retract)
.......................................... 7-277.2.1.2.2 Reverse
Acting Diaphragm (Spring to Extend)
....................................... 7-317.2.1.2.3 Direct Acting
Diaphragm (with Increased Mechanical Advantage) .........
7-357.2.1.2.4 Reverse Acting Diaphragm (with Increased Mechanical
Advantage)...... 7-35
7.2.1.3 Scotch Yoke Actuators (Quarter Turn Valves)
.............................................. 7-367.2.1.3.1 Scotch
Yoke, Double Acting Air
Cylinder................................................
7-367.2.1.3.2 Scotch Yoke, Single Acting Air Cylinder, Spring
Return ........................ 7-39
7.2.1.4 Diaphragm Actuators
(rotary)........................................................................
7-417.2.1.5 Rack and Pinion
Actuators............................................................................
7-45
7.2.1.5.1 Rack & Pinion, Double Acting Air Cylinder,
Rotary................................. 7-457.2.1.5.2 Rack &
Pinion, Single Acting Air Cylinder, Spring Return, Rotary
.......... 7-47
7.2.2 Calculation Considerations
..................................................................................
7-497.2.2.1 Diaphragm
Area............................................................................................
7-497.2.2.2 Spring Rate Degradation
..............................................................................
7-497.2.2.3 Pressure
Drift................................................................................................
7-497.2.2.4
Tolerances....................................................................................................
7-50
7.3 Stroke Time Evaluation
..............................................................................................
7-517.3.1 Increasing Stroke Speed
.....................................................................................
7-51
8 CALCULATING AND EVALUATING MARGINS
............................................................ 8-18.1
Actuator Capability Margin
............................................................................................
8-1
8.1.1 Accounting For Potential Degradation
...................................................................
8-18.1.2
Examples...............................................................................................................
8-2
8.2 Component Allowable
Margin.......................................................................................
8-38.3 Accounting for
Uncertainties.........................................................................................
8-4
8.3.1 Types of Uncertainties
...........................................................................................
8-48.3.2 Applying Uncertainties
............................................................................................
8-5
8.4 Addressing Inadequate
Margin.....................................................................................
8-7
9 AOV
TESTING................................................................................................................
9-19.1 Bench Set
Testing........................................................................................................
9-29.2 Analysis of Static Diagnostic
Traces.............................................................................
9-3
9.2.1 Bench
Set..............................................................................................................
9-89.2.2 Stem Packing
Friction............................................................................................
9-8
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9.2.3 Seat Load
..............................................................................................................
9-99.2.4 Spring Rate
.........................................................................................................
9-109.2.5 Valve Stroke Length
............................................................................................
9-109.2.6 Valve Stroke Time
...............................................................................................
9-119.2.7 Total Unwedging or Unseating Load (Gate and Butterfly
Valves)......................... 9-119.2.8 Other Operating
Parameters................................................................................
9-129.2.9 Analysis of Other Static Test Data
.......................................................................
9-13
9.3 Analysis of Dynamic Diagnostic
Traces......................................................................
9-139.3.1 Opening Against Differential Pressure
.................................................................
9-149.3.2 Closing Under Flow and Differential
Pressure......................................................
9-159.3.3 Analysis of Other Dynamic Test Data
..................................................................
9-16
10
REFERENCES..............................................................................................................
10-1
A VALVE
WORKSHEETS..................................................................................................A-1
B ACTUATOR
WORKSHEETS..........................................................................................B-1
C PACKING LOAD
METHODOLOGY................................................................................C-1C.1
Nomenclature
..............................................................................................................C-1C.2
Methodology................................................................................................................C-2
C.2.1 Rising Stem Packing Loads
.................................................................................C-2C.2.2
Quarter Turn Packing
Loads................................................................................C-2
C.3 Calculation
worksheets............................................................................................C-2
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LIST OF FIGURES
Figure 2-1 AOV Evaluation Methodology
................................................................................
2-3Figure 3-1 Principle Components of Air Operated Valve
......................................................... 3-1Figure
3-2 Basic Flow Path of a Globe Valve
..........................................................................
3-3Figure 3-3 Flow Passages in the
Cage....................................................................................
3-3Figure 3-4 Top Guided Valve
..................................................................................................
3-4Figure 3-5 Flow Curves with Constant Differential
Pressure....................................................
3-4Figure 3-6 Flow Curves Corrected for Piping Losses
..............................................................
3-5Figure 3-7 Equal Percentage Flow
Characteristics..................................................................
3-6Figure 3-8 Three Types of Stem Packing
................................................................................
3-7Figure 3-9 Globe Valve
...........................................................................................................
3-8Figure 3-10 Unbalanced Disc Globe
Valve..............................................................................
3-9Figure 3-11 Balanced Disc Globe Valves
..............................................................................
3-10Figure 3-12 Double Seat Globe
Valve...................................................................................
3-10Figure 3-13 Converging Three-way Valve
.............................................................................
3-11Figure 3-14 Diverging Three-way Valve
................................................................................
3-12Figure 3-15 Piloted Disc Valve
..............................................................................................
3-13Figure 3-16 Gate Valve
.........................................................................................................
3-14Figure 3-17 Butterfly
Valve....................................................................................................
3-15Figure 3-18 Butterfly Valve Body Styles
................................................................................
3-15Figure 3-19 High Performance Butterfly Valve
......................................................................
3-16Figure 3-20 Floating Ball Valve
.............................................................................................
3-18Figure 3-21 Trunnion Mounted Ball Valve
.............................................................................
3-18Figure 3-22 V-Notch ball valve
..............................................................................................
3-19Figure 3-23 Eccentric Rotating Plug Valve
............................................................................
3-20Figure 3-24 Direct Acting Spring and Diaphragm Actuator
.................................................... 3-22Figure
3-25 Reverse Acting Spring and Diaphragm Actuator
................................................ 3-23Figure 3-26
Spring Return Direct Acting Rotary Diaphragm Actuator
.................................... 3-24Figure 3-27 Air Cylinder,
Spring
Return.................................................................................
3-25Figure 3-28 Double Acting Rack and Pinion
Actu..................................................................
3-25Figure 3-29 Scotch Yoke
Actuator.........................................................................................
3-26
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Figure 3-30 Pressure Booster
...............................................................................................
3-27Figure 3-31 Solenoid Valve
...................................................................................................
3-28Figure 5-1 Free Body Diagram of an Unbalanced Globe Valve
............................................... 5-9Figure 5-2 Free
Body Diagram of a Balanced Globe Valve
................................................... 5-14Figure 5-3
Free Body Diagram of a Balanced Globe Valve with Pilot Disc
............................ 5-20Figure 5-4 Free Body Diagram of a
Double Seat Globe Valve
.............................................. 5-23Figure 5-5 Free
Body Diagram of a Three Way Globe
Valve................................................. 5-27Figure
5-6 Hydrodynamic Torque Factor vs Equivalent System
Resistance.......................... 5-38Figure 7-1 Rising Stem
Actuator Type Flowchart
....................................................................
7-6Figure 7-2 Rising Stem Valve and Actuator Position Correlation
Flowchart............................. 7-7Figure 7-3 Valve and
Actuator Position Correlation
Flowchart.................................................
7-8Figure 7-4 Quarter Turn Actuator Type Flowchart
...................................................................
7-9Figure 7-5 Quarter Turn Valve and Actuator Position Correlation
Flowchart ......................... 7-10Figure 7-6 Available Force
Plot for Double Acting Air Cycinder
............................................. 7-12Figure 7-7 Double
Acting Air Cylinder,Rod Extension
...........................................................
7-12Figure 7-8 Double Acting Air Cylinder, Rod
Retraction..........................................................
7-12Figure 7-9 Double Acting Air Cylinder, Double Ended
...........................................................
7-14Figure 7-10 Double Acting Air Cylinder, Direct Acting
...........................................................
7-15Figure 7-11 Double Acting Air Cylinder, Reverse Acting
....................................................... 7-18Figure
7-12 Available Force Plot for Single Acting Air Cylinder
............................................. 7-22Figure 7-13
Single Acting Air Cylinder, Direct Acting, Fully Extended
................................... 7-22Figure 7-14 Single Acting
Air Cylinder, Direct Acting,
Retracted............................................ 7-22Figure
7-15 Single Acting Air Cylinder, Direct Acting, Fully Retracted
................................... 7-22Figure 7-16 Available Force
Plot for Single Acting Air Cylinder, Reverse Acting
................... 7-24Figure 7-17 Single Acting Air Cylinder,
Reverse Acting, Fully Extended................................
7-25Figure 7-18 Single Acting Air Cylinder, Reverse Acting
Retracted......................................... 7-25Figure 7-19
Single Acting Air Cylinder, Reverse Acting, Fully Retracted
............................... 7-25Figure 7-20 Available Force
Plot for Diaphragm
Actuator......................................................
7-27Figure 7-21 Diaphragm Actuator, Fully
Extended..................................................................
7-28Figure 7-22 Diaphragm Actuator ,
Retracted.........................................................................
7-28Figure 7-23 Diaphragm Actuator, Fully Retracted
.................................................................
7-28Figure 7-24 Available Force Plot for Reverse Acting
Diaphragm........................................... 7-31Figure
7-25 Reverse Acting Diaphragm, Fully Extended
....................................................... 7-31Figure
7-26 Reverse Acting Diaphragm, Retracted
...............................................................
7-32Figure 7-27 Reverse Acting Diaphragm, Fully
Retracted.......................................................
7-32Figure 7-28 Direct Acting Diaphragm with Link Arm
..............................................................
7-35Figure 7-29 Reverse Acting Diaphragm with Link Arm
..........................................................
7-36Figure 7-30 Scotch Yoke, Double Acting Air
Cylinder............................................................
7-37
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Figure 7-31 Percentage of Break Torque Plot for Scotch Yoke,
Double Acting ..................... 7-37Figure 7-32 Scotch Yoke,
Single Acting Air Cylinder
.............................................................
7-39Figure 7-33 Percentage of Ending Torque Plot for Scotch Yoke,
Singlele Acting .................. 7-40Figure 7-34 Rotary Diaphragm
Actuator................................................................................
7-42Figure 7-35 Percentage of Ending Torque Plot for Rotary
Diaphragm................................... 7-42Figure 7-36 Double
Acting Rack & Pinion, Rotary
.................................................................
7-46Figure 7-37 Available Torque Plot for Double Acting Rack and
Pinion .................................. 7-46Figure 7-38 Single
Acting Rack and Pinion,
Rotary...............................................................
7-47Figure 7-39 Available Torque Plot for Single Acting Rack and
Pinion.................................... 7-48Figure 8-1 AOV
Margins and Uncertainties
.............................................................................
8-6Figure 9-1 Example AOV Static Test Diagnostic Data Traces
............................................... 9-17Figure 9-2
Example Direct Acting AOV Static Test Diagnostic Data
Plot............................... 9-18Figure 9-3 Analysis of
Example Direct Acting AOV Static Test Data
..................................... 9-19Figure 9-4 Determination
of Unwedging Load from Air Operated Gate Valve Static Test
Data
..............................................................................................................................
9-20Figure 9-5 Analysis of Example Reverse Acting AOV Static Test
Data ................................. 9-21Figure 9-6 Analysis of
Example Double Acting AOV Static Test Data
................................... 9-22Figure 9-7 Example Air
Operated Gate Valve Dynamic Test Data
........................................ 9-23Figure 9-8 Example Air
Operated Gate Valve Dynamic Test Data -
Details........................... 9-24
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LIST OF TABLES
Table 7-1 Parameter
Definitions..............................................................................................
7-3Table 8-1 AOV Component Ratings
........................................................................................
8-4Table A-1 Required Thrust for Unbalanced Disc Globe Valves
(Section 5.4.1) ....................... A-2Table A-2 Required
Thrust for Balanced Disc Globe Valves (Section 5.4.2)
........................... A-4Table A-3 Required Thrust for
Balanced Disc Globe Valves With Pilot Valve (Section
5.4.3)
...............................................................................................................................
A-6Table A-4 Required Thrust for Double Seat Globe Valves (Section
5.4.4)............................. A-10Table A-5 Required Thrust
for Three-Way Globe Valves (Section
5.4.5)............................... A-12Table A-6 Sealing/Wedging
Loads for Gate Valves (Section
5.5).......................................... A-16Table A-7
Required Torque for Ball Valves (Section 5.7)
...................................................... A-18Table
B-1 Actuator Capability Calculation Worksheet (Double Acting Air
Cylinder
Actuator)..........................................................................................................................
B-6Table B-2 Actuator Capability Calculation Worksheet (Single
Acting Air Cylinder
Actuator)........................................................................................................................
B-19Table B-3 Actuator Capability Calculation Worksheet (Diaphragm
Actuator)......................... B-29Table B-4 Actuator
Capability Calculation Worksheet (Diaphragm
Actuator)......................... B-36Table B-5 Actuator
Capability Calculation Worksheet (Diaphragm
Actuator)......................... B-43Table B-6 Actuator
Capability Calculation Worksheet (Diaphragm
Actuator)......................... B-51Table B-7 Actuator
Capability Calculation Worksheet (Scotch Yoke Actuator)
...................... B-59Table B-8 Actuator Capability
Calculation Worksheet (Scotch Yoke Actuator) ......................
B-66Table B-9 Actuator Capability Calculation Worksheet (Rotary
Diaphragm Actuator) ............. B-74Table B-10 Actuator
Capability Calculation Worksheet (Rotary Diaphragm Actuator)
........... B-81Table B-11 Actuator Capability Calculation
Worksheet (Rack & Pinion, Double Acting) ........ B-88Table
B-12 Actuator Capability Calculation Worksheet (Rack & Pinion,
Single Acting) ......... B-91
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INTRODUCTION
1.1 Purpose and ObjectiveThe purpose of the Evaluation Guide is
to present methodology for:
x Defining the functional and design requirements for an
air-operated valve (AOV)and its accessories including code
requirements and design basis/normal operatingconditions.
x Evaluating valve design features that can affect AOV operation
and calculatingvalve thrust/torque requirements.
x Evaluating air actuator design features that can affect AOV
operation, calculatingthe actuator output thrust/torque, and
evaluating the compatibility of the actuatorand the valve.
x Evaluating the available margin between the actuator output
thrust/torque and therequired stem thrust/torque (i.e. capability
margin), and evaluating valve/actuatorsurvivable thrust and
torque.
x Performing and interpreting baseline static and dynamic
testing to confirm actuatoroutput thrust/torque and margin.
In summary, the major objectives of the Evaluation Guide are to
provide: (1) practicalmethods for evaluating whether existing AOVs
meet the design and functionalrequirements for their applications
in nuclear power plants, and (2) suggestedapproaches for resolving
AOV application problems. The guide does not address AOVmaintenance
issues or requirements. Maintenance issues are covered in EPRI
reportNP-7412, Revision 1, Maintenance Guide for Air Operated
Valves, PneumaticActuators, and Accessories (Reference 10.9).
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1.2 Scope of Evaluation Guide
The Evaluation Guide is applicable to Boiling Water Reactors
(BWRs) and PressurizedWater Reactors (PWRs). The Evaluation Guide
covers both nuclear safety-related andnonsafety-related valves.
The Evaluation Guide is applicable to the following valve
designs:
x Globe Valves (Balanced and Unbalanced, 2-way, 3-way, Piloted,
Double seated)
x Gate Valves (Solid wedge, Flexible wedge, Anchor/Darling
double disk, Aloycosplit wedge)
x Butterfly Valves (Symmetric disk and single offset)
x Ball Valves (Floating ball and Trunnion)
While other types are found in nuclear power plants, the four
types covered by theGuide are the most widely used in AOV
applications in United States nuclear powerplants.
The Evaluation Guide is applicable to the following air actuator
types:
x Diaphragm
x Piston
x Rack and Pinion
x Scotch Yoke
These actuators encompass the majority of air actuators found in
the nuclear industry.
1.3 Organization of the Evaluation Guide
The Evaluation Guide is organized to provide a framework around
which a plant-specific AOV evaluation program can be developed. The
Guide contains introductorymaterial, analysis methods for
evaluating AOV performance, and suggested approachesfor resolving
AOV application problems.
Users are strongly encouraged to consult other sources of
information to supplementthe Guide. Good sources include:
x Valve and actuator vendors
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x Other utilities and utility organizations (e.g., AOV Users
Group, AOV Joint OwnersGroup)
x Technical references and reports (such as those listed in
Section 10)
x Reference 10.14 provides a comprehensive summary of all EPRI
PPP researchactivities.
This Guide is organized into ten sections and three appendices,
as follows:
1.3.1 Overview of AOV Evaluation Methodology (Section 2)Section
2 describes an overall approach for evaluating an AOV application.
A flowchartis included defining the path for engineering evaluation
of an AOV.
1.3.2 Functional Description and Introduction to Air-Operated
Valves (Section 3)Section 3 presents a brief introduction to AOVs.
The intent is to provide generalbackground information, including
descriptions of the principal components (valves,actuators, and
accessories) and their operation. Emphasis is placed on
designlimitations and characteristics important to the application
of the AOVs for nuclearplant service. The section provides an
overview of the subject and a basis forunderstanding the
discussions contained in later sections.
The functional description and introduction to AOVs is presented
in the followingsections:
x Valves (Section 3.1)
x Air Actuators (Section 3.2)
x Accessories (Section 3.3)
1.3.3 Definition of AOV Functional and Design Requirements
(Section 4)x Section 4 presents a suggested methodology for
defining the functional and design
requirements for an AOV application. Specific subsections
address definition ofrequirements considering:
x Valve Structural and Design Requirements (Section 4.1)
x Actuator Structural and Design Requirements (Section 4.2)
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x AOV Capability Requirements (Section 4.3)
x Air Supply System Requirements (Section 4.4)
x External Operating Environment (Section 4.5)
x AOV Orientation (Section 4.6)
x AOV Accessibility (Section 4.7)
x Industry Technical Issues (Section 4.8)
1.3.4 Determining Required Thrust or Torque (Section 5)Section 5
presents analytical methods for calculating the required stem
thrust/torque toopen and close AOVs, along with the applicability
and limitations of each method.
There are many valve designs and valve vendors, and the specific
details for aparticular valve may limit the applicability of the
evaluation methods presented in theGuide. The analytical methods do
not cover all possible configurations and carefuljudgment is needed
in applying the equations. In some cases, the valve vendor mayneed
to be consulted to confirm the methods and design inputs that are
used forcalculating required stem thrust/torque.
Methods for evaluating required thrust/torque is presented for
the following valvedesigns:
x Globe Valves (Section 5.4)
x Gate Valves (Section 5.5)
x Butterfly Valves (Section 5.6)
x Ball Valves (Section 5.7)
Calculation sheets for applying the methods presented in this
section are provided inAppendix A.
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1.3.5 Evaluation of Valve / Actuator Rated and Survivable Thrust
and Torque(Section 6)Section 6 presents considerations for
determining the valve rated thrust and torque andthe valve
survivable thrust and torque. In addition, considerations for the
functionaland structural ratings/limits for the actuator and
accessories are presented.
1.3.6 Evaluation of Air Actuator Output Thrust / Torque
Capability (Section 7)Section 7 presents analytical methods for
calculating the thrust/torque capability foreach style of actuator,
along with methods for evaluating stroke time.
The evaluation of air actuators is presented in the following
sections:
x Required Input Information (Section 7.1)
x Actuator Output Capability Evaluations (Section 7.2)
x Stroke Time Evaluation (Section 7.3)
1.3.7 Calculating and Evaluating Margins (Section 8)Section 8
discusses methods for determining AOV operating margins and
illustrateshow the various margins are related.
x Actuator Capability Margin (Section 8.1)
x Component Allowable Margin (Section 8.2)
x Accounting for Uncertainties (Section 8.3)
x Addressing Inadequate Margin (Section 8.4)
1.3.8 AOV Testing (Section 9)Section 9 presents both static and
dynamic testing techniques to determine actual valveloads, and
includes recommended measurements and interpretation of test
results.
The AOV testing is presented in the following sections:
x Bench Set Testing (Section 9.1)
x Static Testing to confirm actuator output capability and setup
(Section 9.2)
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x Dynamic Testing to confirm operating loads (Section 9.3)
1.3.9 References (Section 10)
1.3.10 Appendices
Appendix A presents valve calculation worksheets. These
worksheets summarize theinformation provided in Section 5.0 for
each type of valve arrangement and provide theuser with an
organized and systematic approach for evaluating valve
thrust/torque.
Appendix B presents actuator vendor data sheets and calculation
worksheets. Thevendor data sheets present a convenient and
systematic approach for gathering actuatorrequired information from
vendors. For the users convenience, variables were left offone set
of data sheets for their actual use in the field. The worksheets
summarize theinformation provided in Section 7.0 for each type of
actuator arrangement and providethe user with an organized and
systematic approach for evaluating actuatorthrust/torque.
Appendix C presents methodology for determining packing load for
both rising stemand quarter turn valves, along with calculation
worksheets.
1.4 Basis for Guide
The Evaluation Guide addresses the principal known industry
issues related to theapplication of AOVs. Guidance for addressing
these issues incorporates:
x Lessons learned and methods developed as part of the EPRI MOV
PerformancePrediction Research Program (Reference 10.2).
x Lessons learned as part of utility implementation of NRC
Generic Letter 89-10requirements.
x Lessons learned and methods developed during implementation of
EPRI Pilot AOVprograms at several plant sites.
x Review of published research.
x Review of NRC and AEOD publications related to MOV and AOV
performance.
x Review of valve and actuator manufacturers information and
publications.
x Input from a Technical Advising Group made up of utility MOV
and AOVengineers.
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Lessons learned from EPRI and utility Motor Operated Valve (MOV)
programs andpilot EPRI AOV programs show that AOV performance and
reliability could beenhanced via improvements in sizing, setup,
testing, and maintenance practices. Someof the specific
observations include:
x Thrust requirements for gate valves may have been under
predicted during initialsizing.
x The appropriate area (seat vs. guide) needs to be chosen for
differential pressureapplications for unbalanced globe valves.
x The side loading algorithm in the EPRI balanced globe valves
modeled may beoverly conservative for some valve designs.
x Butterfly valve bearing coefficients may have degraded from
those values used insizing.
x Packing loads may be a significant contributor to the required
operating loads.Changes in packing material or gland stress may be
critical.
x Spring safe loads need to be considered if changes to vendor
supplied preloads aremade.
x This guide addresses these issues and provides guidance for
evaluating AOVapplications in nuclear power plant service.
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2
OVERVIEW OF AOV EVALUATION METHODOLOGY
The AOV Evaluation Guide provides a comprehensive synopsis of
the evaluationtechniques which have been developed, to date, from
pilot EPRI AOV technicalevaluation projects. Additionally, the
guide provides design and testing considerationsto be accounted for
based on available industry experience and other EPRI
documentsrelated to the verification of proper AOV actuator sizing
and set point establishmentunder normal and accident conditions in
Nuclear Power Plants. This Evaluation Guideis designed to be used
by everyone from the novice to the expert, and the trades personto
the professional. Thus, there are numerous ways of using the Guide.
Figure 2-1provides one logical flow path for the guides use. The
numbers inside the decisionblocks refer to the applicable section
numbers.
The user begins at Start in the Flow Chart and proceeds to
define AOVdesign/functional requirements and characteristics. A
comparison is made between theAOV characteristics and the system
requirements (such as pressure, temperature, andEQ requirements) to
ensure the appropriate AOV application. If the AOVscharacteristics
are not appropriate, then the function requirements are
reconsidered orthe AOV is modified. The worst case system operating
requirements are thenestablished based on the valves functional
review (Section 4.3). Using theserequirements, determine the
required stem thrust / torque using the methods providedin Section
5.0. Next, the actuator output capability is determined using the
requiredinputs (Section 7.1) and methods presented in Section 7.2.
The resultant ActuatorOutput Capability is calculated using methods
from Section 8.1. The user must takeinto consideration
uncertainties associated with input parameters and / or
potentialdegradation of valve / actuator performance. Consideration
for these uncertainties anddegradations can be applied directly
into the margin calculation or accounted for in theacceptance
criteria. Section 8.4 provides guidance on margin enhancement.
In addition to Actuator Output Capability Margin, one must
consider structural and/orperformance limits of the valve, actuator
and accessories. Section 8.2 provides methodsfor evaluation of the
Component Allowable Margin. Section 8.4 also provides guidanceon
margin enhancement.
If the component and actuator margins are not adequate,
adjustments are made to thevalve / actuator to increase the margin
(Section 8.4). If adjustments to the valve /actuator will not give
adequate margin or are not feasable, then evaluate conservative
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assumptions in system conditions or component inputs and
re-calculate componentcapabilities. This starts the process over
again.
After adequate actuator / component margin has been established,
set up and designinput assumptions should be confirmed by testing
or other engineering analysis(Section 9.1, 9.2).
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Define AOV design/functional requirements and AOV
characteristics (4.1 through 4.8)
For the valve determine: Required stem thrust/ torque
(5.1-5.7)
Valve thrust/torque limits (6.0)
For the actuator determine: Actuator output capability (Min.
& Max.) (7.2)
Actuator thrust/ torque limits (6.2)
Obtain a match between the AOV functional / design requirements
and AOV characteristics by:
Developing an engineering justification for changing the
design/functional requirements
or modifying the AOV
Make adjustments or modifications to valve and / or actuator
using the guidance of Section 8.4.
Are the AOV characteristics compatible with
design/functional requirements?
Is the Actuator Capability Margin sufficient including
potential
degradations and uncertainties? (8.2)
No
Yes
Start
For the Accessories determine: Pressure ratings (8.2)
Temperature ratings
No
Is the Component Allowable Margin sufficient including potential
degradation
and uncertainties? (8.1)
No
Yes
Confirm AOV set up and design input assumptions by testing or
other engineering analysis as required.
(9.1, 9.2)
End
Will the adjustments give adequate Component and
Actuator margin?
Yes
No
Evaluate conservative assumptions in system conditions and
actuator / valve inputs to increase
Actuator and Valve margins.
Determine worst case system requirements for the valve's
operation based on the functional review
(4.3.4)
Yes
Figure 2-1AOV Evaluation Methodology
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FUNCTIONAL DESCRIPTION AND INTRODUCTION TO
AIR-OPERATED VALVES
3.1 Valves
This section describes rising stem gate and globe valves along
with quarter turn valvescommonly used for AOV applications in
nuclear power plants. Air operated valves areused extensively in
the power generation industry for process control and
systemisolation functions. Proper operation of these valves is
critical to running a safe,dependable, and economic plant. This
section is included to provide the user with anunderstanding of the
principle components of common air operated valves (see
Figure3-1).
Figure 3-1Principle Components of Air Operated Valve
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Valve
Linear (Gate or Globe)
Quarter Turn (Butterfly or Ball)
Air Actuator
Linear (Diaphragm or Piston)
Rotary (Diaphragm or Piston with rotary transmission)
Controls
Solenoid Valve
Positioner
Speed controls
Position transmitter
I/P converter
Supply System
Volume Boosters
3.1.1 Globe Valves (unbalanced, balanced, double seat,
three-way, piloted)A globe valve uses a cylindrical or spherical
shaped, tapered disc or plug. In a globevalve the fluid must change
direction several times. With the direction change, the discmoves
parallel to the flow when opening and closing the valve. The
advantage of theglobe valve is that it is well suited for flow
regulation. Fluid flow begins as soon as thedisc and seat separate,
allowing for a more efficient throttling of flow with a minimumof
seat erosion. In some cases, such as small valves, globe valves are
used for isolation,since the availability of small gate valves is
limited. The disadvantage of globe valves isthat they have a higher
flow resistance (higher pressure drop) than gate valves due tothe
abrupt changes in the flow paths in the globe valves. The basic
flow path of a globevalve is depicted in Figure 3-2.
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Figure 3-2Basic Flow Path of a Globe Valve
Note: Valves that are used as block valves to isolate a section
of a piping system are generallyrequired to provide tight shutoff.
Globe valves are typically designed to modulate flow and
oftenoperate in mid-flow or at a throttled position. These valves
are typically built to withstandprocess pressures and high-cycle
service but are not designed for tight shutoff.
Desired flow characteristics can be obtained by changing the
shape of the flow passagesin the cage (Figure 3-3) and by replacing
or modifying the valve disc and seat in topguided valves (Figure
3-4).
Figure 3-3Flow Passages in the Cage
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Figure 3-4Top Guided Valve
These changes in trim components affect the flow characteristics
of the valve. The threemost common trim types are equal percentage,
linear operation, and quick open.Figure 3-5 shows typical flow
curves for these trim types with a constant differentialpressure
across the valve. Figure 3-6 shows the flow curves adjusted for
typical pipinglosses. The objective of trim selection is to obtain
optimum process control. A generalrule of thumb is to select a
linear flow characteristic if the pressure drop is constant
withincreasing flow rate and an equal percent characteristic when
the differential pressuredecreases with increasing flow rate.
Figure 3-5Flow Curves with Constant Differential Pressure
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Figure 3-6Flow Curves Corrected for Piping Losses
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Equal percentage trim is most commonly used because many systems
use centrifugalpumps. In these systems, an increase in flow rate
results in decreased pressure drop atthe control valve based on the
head/flow characteristic of the pump. The flowcharacteristic for
equal percentage resembles Figure 3-7.
Figure 3-7Equal Percentage Flow Characteristics
Quick Open trim is used for On-Off applications and provides
maximum flow quickly.
If a valve does not appear to fit the existing process
conditions, check with amanufacturer's technical representative or
with a valve services vendor. Many timesthe exchange of trim can be
accomplished at the next outage at a reasonable cost.
Stem packing is used to seal the stem opening in the bonnet, and
the gland is used topre-load the stem packing. The packing may be
live loaded (e.g., by Belleville springs),pressure energized or
torque preloaded (e.g., by torquing the gland bolts). Live
loadedpacking uses springs to maintain a nearly constant load on
the packing even though thepacking may shrink. Shrinkage may be due
to thermal expansion, aging, andconsolidation. Pressure energized
packing is usually a TFE V-ring type lip seal. Thispacking has some
initial loading from the spring and system pressure is used to seal
thepacking lip to the packing box wall and valve stem. Square
compression packing relieson the compressive force exerted on the
packing by tightening the packing gland bolts.All three types are
shown in Figure 3-8.
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Live Loaded Pressure Energized
Torque PreloadedFigure 3-8Three Types of Stem Packing
The stem is a shaft that has a smooth portion that passes
through the packing and athreaded portion that engages the actuator
coupling. The valve disc has a hardenedsurface, which contacts the
seat ring to provide sealing.
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Components of a typical T-pattern unbalanced globe valve, as
shown in Figure 3-9,include the valve body, bonnet, gland, stem
packing, stem, disc (plug), and seat. For Y-pattern globe valves,
the stem is not perpendicular to the piping. The body, bonnet,yoke,
stem, and stem packing function are as described previously for the
Tee patternvalve.
1. Plug Stem 7. Spacer 13. Seat Ring2. Packing Box Studs 8.
Bonnet 14. Valve Plug3. Packing Box Stud Nuts 9. Valve Body Studs
15. Plug Stem Pin4. Packing Flange 10. Valve Body Stud Nuts 16.
Body5. Packing Follower 11. Valve Body Gaskets 17. Drive Nut6.
Packing 12. Guide Bushing
Figure 3-9Globe Valve
3.1.1.1 Unbalanced Disc Globe Valves
In unbalanced trim (Figure 3-7), upstream pressure is fully
applied to one side of thedisc and downstream pressure to the
other. The result is that the full valve pressuredifferential is
taken across the disc. In high-pressure drop applications, the
force can beconsiderable, requiring a very large actuator to
operate the valve disc.
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Figure 3-10Unbalanced Disc Globe Valve
3.1.1.2 Balanced Disc Globe Valves
Balanced disc globe valves have openings or "pressure balancing"
ports drilled throughthe disc (Figure 3-11). The ports allow
pressure to equalize above and below the disc,lessening the
differential pressure load and allowing the use of smaller
actuators. Pistonor seal rings generally provide a seal between the
area above the disc and the outletport. Many air-operated balanced
disc globe valves are cage guided.
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Figure 3-11Balanced Disc Globe Valves
3.1.1.3 Double Seat Globe Valves
Double seat valves are considered semi-balanced trim
designs,(Figure 3-12). Double seatedvalves have two discs and two
ports of slightly different diameters. Due to the two portdesign,
hydrodynamic forces on the valve discs tend to cancel each other
out, except for thedifference in disc seat diameters.
Figure 3-12Double Seat Globe Valve
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3.1.1.4 Three-Way Globe Valves
Three way valves are also called converging or diverging valves
depending on how thevalve is installed. Three-way valves have three
separate ports. In converging three-way valves (Figure 3-13), the
fluid flows into the common port from one or both of theother ports
(mixing the fluids). These valves are generally designed with a
single disc(with two seats) positioned between the body seats so
that flow is under the seat forboth discs. V-ported discs may be
used to provide more accurate control of the flow.Converging valves
can only isolate flow of one inlet port at a time. The other port
willbe open.
Figure 3-13Converging Three-way Valve
In diverging valves (Figure 3-14), the fluid flows from the
common port to one or bothof the other two ports (diverting the
flow). These valves are generally designed withtwo discs, one on
each side of the body seats so that flow is under the seat for
bothdiscs. As in converging valves, V-ported discs may be used to
provide more accuratecontrol of the flow. Diverging valves can only
isolate flow to one inlet port at a time.The other port will be
open.
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Figure 3-14Diverging Three-way Valve
3.1.1.5 Balanced Disc Globe Valves With Pilot
Piloted globe valves are special application valves used when
high shutoff capabilityand reduced differential pressure loading is
required. These valves are typicallydesigned to work properly only
when installed with flow overseat. For the closingstroke, a spring
between the pilot disc and the main disc keeps the pilot valve
openuntil the main disc hits the body seat. At this point, the
actuator must provide thrust tocompress the pilot spring and close
the pilot valve. With the main disc and pilot discclosed, upstream
pressure leaks past the disc seal ring to the cavity above the main
disc.This pressure then aids in the sealing force applied to both
discs. For the openingstroke, the actuator first lifts the pilot
disc, allowing the pressure to equalize above andbelow the main
disc, creating a balanced disc. Since the main disc acts as a
balanceddisc valve, a smaller actuator can be used for these
valves. An example of a piloted discis shown in Figure 3-15.
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Figure 3-15Piloted Disc Valve
3.1.2 Gate Valves
A gate valve uses a gate-like disc, or wedge, to stop the flow.
The disc movesperpendicular to the direction of flow during opening
and closing. Gate valves areused for isolation and initiation of
flow. One advantage of the gate valve is that it canaccommodate
full flow without a restriction in the pipe, resulting in a low
piping flowresistance (low-pressure drop). Additional advantages of
gate valves is that they aresmall in size compared to a globe
valve, useful for applications where the valve is usedonly to shut
off flow, and often cost less. Also, the operating force for a gate
valve isusually less than for an unbalanced disc globe valve. A
disadvantage of the gate valveis that it is not as well suited for
throttling service as a globe valve. Gate valves are
alsosusceptible to pressure locking and thermal binding.
The components of a typical bolted bonnet gate valve are shown
in Figure 3-16. Theyinclude the valve body, bonnet, yoke, stem
packing, gland, stem, disc (wedge),backseat, T-slot connection, and
seat rings. The valve body, bonnet, andbody-to-bonnet bolting form
the major part of the piping system pressure boundary forthe valve
assembly. The stem-packing chamber in the bonnet allows the stem
topenetrate into the valve body. The yoke is used to connect the
operator to the valvebody or bonnet.
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Figure 3-16Gate Valve
Stem packing is used to seal the stem opening in the bonnet, and
the gland is used topreload the stem packing. The packing may be
live loaded (e.g., by Belleville springs)or torque preloaded (e.g.,
by torquing the gland bolts) as shown in Figure 3-8. Liveloaded
packing uses springs to maintain a nearly constant load on the
packing eventhough the packing may shrink. Shrinkage may be due to
thermal expansion, aging, orconsolidation.
The stem is a shaft that has a smooth portion that passes
through the packing and athreaded portion that engages the actuator
coupling. Typically the stem is attached tothe valve disc by a "T"
slot connection. The valve disc has two hardened seatingsurfaces,
which engage with the seat rings. These surfaces are the sealing
surfaces ofthe valve.
Gate valves normally have a backseat, which can be used to seal
the stem to the bonnet,when the valve is in the fully open
position. The backseat seal is provided formaintenance
purposes.
3.1.3 Butterfly Valves
Butterfly valves are high pressure recovery valves. They offer
minimal friction lossesdue to the location of the disc in the
center of flow at the full open position. Butterflyvalves allow
more flow with less pressure drop than globe valves. Figure 3-14
shows aconventional symmetric disc butterfly valve. When the disc
is rotated 90 degrees fromthe closed position, the disc is in-line
with the process flow and adds very little pressuredrop or
turbulence.
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Figure 3-17Butterfly Valve
Butterfly valves are constructed into three different body
styles; wafer style, lugged,and flanged (Figure 3-18). The wafer
style is lighter, requires very little additionalpiping support,
and is easy to install. The main benefit of the lugged style is the
ease ofinstallation. They are typically used for end-of-line
installations. Flanged butterflyvalves provide much greater support
for the valve but require additional strengthpiping for valve
support.
Wafer Lugged Flanged
Figure 3-18Butterfly Valve Body Styles
High performance butterfly valves are similar in principle to
conventional models.Their high performance distinction results from
the incorporation of an offset (eccentric)disc in conjunction with
pressure assisted seals (Figure 3-19).
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Figure 3-19High Performance Butterfly Valve
Most high performance discs are double offset; that is, the
shaft is offset from the planeof the sealing surface and it is also
offset from the center of the body bore. The doubleoffset swings
the disc face away from the seal during the initial 10 to 15
degrees ofrotation and minimizes disc to seal contact throughout
the remainder of rotation. Thisminimizes the possibility of
permanent depressions in the seal caused by prolongeddisc to seal
contact. The disc must be rotated in the proper direction and
should neverbe permitted to overtravel. These two actions are the
most frequent causes ofpermanent seal damage. Proper sealing
depends on the very fine finish between thedisc and the sealing
edge.
Pressure assisted seals require a minimum pressure drop across a
closed valve tomaintain the rated shutoff. To seal, process
pressure is ported behind the seal, forcingthe seal against the
sealing edge of the disc. As pressure is increased, shutoff
becomestighter and tighter. Seals are available for various
materials and configurations. PTFEseals are used for tight shut off
(ANSI/FCI 70-2 Class VI shut off) at temperatures up to450 F. The
seals are supported by stainless steel springs that compensate for
wear anddistortion; stainless steel spring seals are used between
450 F and 1000 F with reducedshutoff capabilities.
The shaft is a round bar that has a smooth portion that passes
through the packing anda keyed portion that engages the actuator
coupling. Typically the shaft is attached tothe valve disc by a
keyed, pinned or bolted connection. The valve disc has a
seatingsurface that contacts a seating surface in the valve body
when in the closed position.The seating surfaces may be of a
corrosion resistant material (e.g. stainless steel, Monel,inconel)
or may be a combination of a corrosion resistant and an elastomer
or plasticmaterial (e.g. rubbers or Teflon).
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A butterfly valve is a pipeline flow control device that
operates by rotating what isessentially a thin circular disc within
the pipe on a major diametrical axis of the disc.The disc is
supported in the valve body by a shaft and two sleeve bearings
located intwo valve body trunnions. The shaft may be a single or
two piece construction. Fullstroke (open to closed) disc rotation
is essentially through a 90 arc. (Note: Not all valvedesigns travel
the full 90.) When the disc is parallel to the pipe axis, full
pipeline flowresults. This position is referred to as the full open
or 90 open position. When the discis perpendicular to the pipe
axis, the valve is closed; there is no flow and the edge of thedisc
comes into contact with a seal in the valve body. This position is
referred to as thefully closed or zero degree (0) position. The
disc is rotated within the valve body bythe actuator shaft that
extends through the valve body to its exterior where an
actuatingdevice is mounted on the body trunnion to rotate and hold
the valve disc in the fullopen, full closed or intermediate
positions. Larger valves have thrust bearings thatcenter and
support the disc and shaft as well as the fluid pressure end loads
on thevalve shaft.
Shaft packing is used to seal the shaft opening(s) in the valve
body. The shaft willpenetrate the body at the actuator connection
trunnion but may not penetrate to theexterior of the body at the
non-actuated body trunnion. Therefore there may be one ortwo
packing glands. In pull down or compression style packing, a gland
is used topreload the shaft packing. The packing may be either live
loaded (e.g., by Bellevillesprings) or torque preloaded (e.g., by
torquing the gland bolts) as shown in Figure 3-5.Live loaded
packing glands use springs to maintain a nearly constant load on
thepacking even though the packing may shrink. Shrinkage may be due
to thermalexpansion, aging, or consolidation. Packing may also be
of the chevron or o-ring style.These packing types are generally
compressed by the physical dimensions of the glandor groove and are
pressure activated or loaded to seal. This style of packing
glanddoes not generally have springs or mounting bolts that permit
adjustment.
3.1.4 Ball Valves
Ball Valves use a full or partial sphere as a plug that rotates
within the valve body tothrottle the flow. Four basic styles are
presented: floating ball, trunnion mounted,V-notch, and eccentric
rotating plug valves. These valves are used where high
capacity,tight shutoff, and minimal pressure loss are desired.
Floating ball valves (Figure 3-20) control flow with a rotating
sphere. The valve's boreis slightly reduced below the piping size,
allowing the valve to immediately controlflow as it is rotated from
the fully open or fully closed position. Because this design hasno
bearing above or below the ball, the DP load across the valve
pushes the ball againstthe valve seat, causing it to seat. The ball
is typically preloaded between the seats tominimize the effect of
DP on the ball loads.
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Figure 3-20Floating Ball Valve
Trunnion mounted ball valves (Figure 3-21) support the ball with
a bearing supportedtrunnion instead of relying upon the valve
seats, as in a floating ball valve. With thetrunnion carrying the
differential pressure across the valve, lower actuation torque
isrequired and hence the trunnion mounted ball valves can be used
for higher pressuresand larger sized valves.
Figure 3-21Trunnion Mounted Ball Valve
Shaft seals prevent upstream pressure from leaving the shaft
bores. These sealsperform the same job as packing does for other
types of valves. Seats and/or flow ringsprovide a seal between the
ball and the valve ports.
Some ball valves have a single soft-seal design, which provides
a pressure-assisted sealwhen fluid flows toward the seal. A metal
protector ring is commonly used to protectthe seal from damage.
Shims between the valve body and the ball seal determine the
fitbetween the seals and ball.
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Some ball valves have a double soft seal design, which provides
tight shutoff in eitherflow direction. This seal also provides a
"block and bleed" feature, which allows thebody to be bled of any
internal pressure as a means of checking seal integrity, or to
bepurged between uses. A metal flow ring can be used when
conditions dont allow theuse of soft seals; such as in high
temperature or corrosive service. Because no seal isused, the flow
ring has some clearance with the ball and only moderate shutoff can
beobtained.
A V-Notch ball valve is a modification to a standard ball valve
where a "V" shapednotch is cut out of the ball face. The geometry
of the V-Notch valve ball segment(Figure 3-22) combines with the
straight through flow path of a ball valve to providewide range
ability or the ability to control both very low flow rates and very
high flowrates. Flow is controlled from when the notch just begins
to expose the port to the fullopen position. The V-Notch ball
segment is supported and positioned by a drive shaftand a
guidepost. The drive shaft and ball are attached with a splined
connection. Theball's opposite side is supported by a guidepost. A
gasket between the guidepost andthe body prevents leakage. Packing
arrangements of different materials are available toseal the shaft
and prevent leakage of fluid to the atmosphere. The main shaft
bushingwhich supports the drive shaft is precisely located to keep
the ball segment aligned inthe center of the body for proper
contact with the seals. The seals are generallyshimmed to zero
deflection, meaning the seal is just in contact with the ball.
Figure 3-22V-Notch ball valve
Sealing can be accomplished with stainless steel seals to
temperatures of 1000 F withleakage less than ANSI/FCI 70-2 Class IV
leak allowance. Stainless steel seals havelimited pressure drop
ratings. Composition seals of PTFE and polymer binders providetight
shutoff at temperatures below 450 F. Because of their ability to
control a widerange of flow rates, these valves work well in steam
and drain service.
Shaft packing is used to seal the shaft opening(s) in the valve
body. The shaft willpenetrate the body at the actuator connection
trunnion but may not penetrate to theexterior of the body at the
non-actuated body trunnion. Therefore there may be one or
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two packing glands. In pull down or compression style packing a
gland is used topreload the shaft packing. The packing may be
either live loaded (e.g., by Bellevillesprings) or torque preloaded
(e.g., by torquing the gland bolts) as shown in Figure 3-8.Live
loaded packing glands use springs to maintain a nearly constant
load on thepacking even though the packing may shrink. Shrinkage
may be due to thermalexpansion, aging, or consolidation. Packing
may also be of the chevron or o-ring style.These packing types are
generally compressed by the physical dimensions of the glandor
groove and are pressure activated or loaded to seal. This style of
packing glanddoes not generally have springs or mounting bolts that
permit adjustment.
3.1.5 Plug Valves
Eccentric rotating plug valves (Figure 3-23) are designed
specifically for flow controland erosive service. They have an open
flow path and can be made of durablematerials.
Rotating plug valves differ from other ball valves in that the
ball segment or discoperates on an eccentric path. This keeps the
plug out of contact with sealing surfacesduring throttling. This
design helps reduce seat wear and requires less
operatingtorque.
The valve seat design uses a solid metal shutoff surface without
thin elastomer or metalseals to erode in service. On more advanced
designs, the seat is held in position by aretainer but is allowed
to float. The plug closing against it centers the seat ring.
Thisself-centering feature eliminates many alignment problems
during maintenance.
The seat ring is symmetrical and can be reversed to provide a
new seating surface. Thisfeature provides economical extra life and
extended shutoff capability.
Figure 3-23Eccentric Rotating Plug Valve
The shaft is a round bar that has a smooth portion that passes
through the packing anda keyed portion that engages the actuator
coupling. Typically the shaft is attached to
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the valve disc by a keyed, pinned or bolted connection. The
valve disc has a seatingsurface that contacts a seating surface in
the valve body when in the closed position.The seating