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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.

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  • 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 OWNEDRIGHTS, INCLUDING ANY PARTY'S INTELLECTUAL PROPERTY, OR (III) THAT THIS PACKAGE IS SUITABLETO ANY PARTICULAR USER'S CIRCUMSTANCE; OR

    (B) ASSUMES RESPONSIBILITY FOR ANY DAMAGES OR OTHER LIABILITY WHATSOEVER (INCLUDINGANY CONSEQUENTIAL DAMAGES, EVEN IF EPRI OR ANY EPRI REPRESENTATIVE HAS BEEN ADVISEDOF THE POSSIBILITY OF SUCH 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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    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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    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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    1

    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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    3

    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