Control valve handbook

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Control valve handbook

  1. 1. CONTROL VALVE HANDBOOK Fourth Edition
  2. 2. NORTH AMERICA LATIN AMERICA Emerson Process Management Emerson Process Management Marshalltown, Iowa 50158 USA Sorocaba, Sao Paulo 18087 Brazil T 1 (641) 754−3011 T +(55)(15)238−3788 F 1 (641) 754−2830 F +(55)(15)228−3300 www.EmersonProcess.com/Fisher www.EmersonProcess.com/Fisher EUROPE MIDDLE EAST & AFRICA Emerson Process Management Emerson FZE Cernay 68700 France Dubai, United Arab Emirates T +(33) (0)3 89 37 64 00 T +971 4 883 5235 F +(33) (0)3 89 37 65 18 F +971 4 883 5312 www.EmersonProcess.com/Fisher www.EmersonProcess.com/Fisher ASIA PACIFIC Emerson Process Management Singapore 128461 Singapore T +(65) 6777 8211 F +(65) 6777 0947 www.EmersonProcess.com/FisherFisher is a mark owned by Fisher Controls International LLC, a member of the EmersonProcess Management business division of Emerson Electric Co. The Emerson logo is atrademark and service mark of Emerson Electric Co. All other marks are the property of theirrespective owners.The contents of this publication are presented for informational purposes only, and whileevery effort has been made to ensure their accuracy, they are not to be construed aswarranties or guarantees, express or implied, regarding the products or services describedherein or their use or applicability. We reserve the right to modify or improve the designs orspecifications of such products at any time without notice.Neither Emerson, Emerson Process Management nor any of their affiliated entities assumesresponsibility for the selection, use and maintenance of any product. Responsibility for theselection, use and maintenance of any product remains with the purchaser and end-user.Printed in U.S.A.EFisher Controls International LLC 2005D101881X012ii
  3. 3. Preface to Fourth EditionControl valves are an increasingly vital component of modern manufacturing aroundthe world. Properly selected and maintained control valves increase efficiency, safe-ty, profitability, and ecology.The Control Valve Handbook has been a primary reference since its first printing in1965. This fourth edition presents vital information on control valve performance andthe latest technologies. D Chapter 1 offers an introduction to control valves including definitions for common control valve and instrumentation terminology. D Chapter 2 develops the vital topic of control valve performance. D Chapter 3 covers valve and actuator types. D Chapter 4 describes digital valve controllers, analog positioners, boosters, and other control valve accessories. D Chapter 5 is a comprehensive guide to selecting the best control valve for an application. D Chapter 6 covers the selection and use of special control valves. D Chapter 7 covers desuperheaters, steam conditioning valves, and turbine bypass systems. D Chapter 8 offers typical control valve installation and maintenance proce- dures. D Chapter 9 includes information on control valve standards and approval agencies throughout the world. D Chapter 10 offers useful tables of engineering reference data. D Chapter 11 includes piping reference data. D Chapter 12 is a handy resource for common conversions.The Control Valve Handbook is both a textbook and a reference on the strongest linkin the control loop: the control valve and its accessories. This book includes exten-sive and proven knowledge from leading experts in the process control field includ-ing contributions from the ISA and the Crane Company. iii
  4. 4. iv
  5. 5. Table of ContentsChapter 1. Introduction to Control Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 What Is A Control Valve? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Process Control Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Sliding-Stem Control Valve Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Rotary-Shaft Control Valve Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Control Valve Functions and Characteristics Terminology . . . . . . . . . . . . . 16 Other Process Control Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Chapter 2. Control Valve Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Process Variability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Dead Band . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Actuator-Positioner Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Valve Response Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Valve Type And Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Valve Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Economic Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Chapter 3. Valve and Actuator Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Control Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Globe Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Single-Port Valve Bodies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Balanced-Plug Cage-Style Valve Bodies . . . . . . . . . . . . . . . . . . . . . . 43 High Capacity, Cage-Guided Valve Bodies . . . . . . . . . . . . . . . . . . . . 43 Port-Guided Single-Port Valve Bodies . . . . . . . . . . . . . . . . . . . . . . . . . 44 Double-Ported Valve Bodies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Three-Way Valve Bodies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 v
  6. 6. Table of Contents Rotary Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Butterfly Valve Bodies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 V-Notch Ball Control Valve Bodies . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Eccentric-Disk Control Valve Bodies . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Eccentric-Plug Control Valve Bodies . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Control Valve End Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Screwed Pipe Threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Bolted Gasketed Flanges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Welding End Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Valve Body Bonnets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Extension Bonnets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Bellows Seal Bonnets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Control Valve Packing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 PTFE V-Ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Laminated and Filament Graphite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 USA Regulatory Requirements for Fugitive Emissions . . . . . . . . . . . . . 53 Single PTFE V-Ring Packing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 ENVIRO-SEALR PTFE Packing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 ENVIRO-SEALR Duplex Packing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 KALREZR Packing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 ENVIRO−SEALR Graphite ULF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 HIGH-SEALt Graphite ULF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 ENVIRO-SEALR Graphite for Rotary Valves . . . . . . . . . . . . . . . . . . . . . 57 Graphite Ribbon for Rotary Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 Characterization of Cage-Guided Valve Bodies . . . . . . . . . . . . . . . . . . . . . . 58 Characterized Valve Plugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 Valve Plug Guiding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 Restricted-Capacity Control Valve Trim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 Actuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 Diaphragm Actuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 Piston Actuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 Electrohydraulic Actuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 Manual Actuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 Rack and Pinion Actuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 Electric Actuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64Chapter 4. Control Valve Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 Positioners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 Other Control Valve Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 Limit Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 Solenoid Valve Manifold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 Supply Pressure Regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 Pneumatic Lock-Up Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 Fail-Safe Systems for Piston Actuators . . . . . . . . . . . . . . . . . . . . . . . . . . 72 Electro-Pneumatic Transducers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 Electro-Pneumatic Valve Positioners . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72vi
  7. 7. Table of Contents Diagnostics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74Chapter 5. Control Valve Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 Valve Body Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 Designations for the High Nickel Alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 Pressure-Temperature Ratings for Standard Class . . . . . . . . . . . . . . . . . . . 78 Cast Carbon Steel (ASTM A216 Grade WCC) . . . . . . . . . . . . . . . . . . . . 78 Cast Chromium-Molybdenum Steel (ASTM A217 Grade WC9) . . . . . . 79 Cast Chromium-Molybdenum Steel (ASTM A217 Grade C5) . . . . . . . . 80 Cast Type 304 Stainless Steel (ASTM A351 Grade CF3) . . . . . . . . . . . 81 Cast Type 316 Stainless Steel (ASTM A351 Grades CF8M and CG8M) 82 Pressure-Temperature Ratings for ASTM A216 Cast Iron Valves . . . . . . . 84 Pressure-Temperature Ratings for ASTM B61 and B62 Cast Bronze Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Face-to-Face Dimensions for Flanged Globe-Style Control Valves . . . . . 86 Face-to-Face Dimensions for Buttweld-End Globe-Style Control Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 Face-to-Face Dimensions for Socket Weld-End Globe-Style Control Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 Face-to-Face Dimensions for Screwed-End Globe-Style Control Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 Face-to-Centerline Dimensions for Raised Face Globe-Style Angle Control Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 Face-to-Face Dimensions for Separable Flanged Globe-Style Control Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 Face-to-Face Dimensions for Flangeless, Partial-Ball Control Valves . . . 91 Face-to-Face Dimensions for Single Flange (Lug-Type) and Flangeless (Wafer-Type) Butterfly Control Valves . . . . . . . . . . . . . . . . . . . . 91 Face-to-Face Dimensions for High Pressure Butterfly Valves with Offset Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 Wear & Galling Resistance Chart Of Material Combinations . . . . . . . . . . . 92 Control Valve Seat Leakage Classifications . . . . . . . . . . . . . . . . . . . . . . . . . 93 Class VI Maximum Seat Leakage Allowable . . . . . . . . . . . . . . . . . . . . . . . . 94 Typical Valve Trim Material Temperature Limits . . . . . . . . . . . . . . . . . . . . . . 94 Service Temperature Limitations for Elastomers . . . . . . . . . . . . . . . . . . . . . 95 Ambient Temperature Corrosion Information . . . . . . . . . . . . . . . . . . . . . . . 96 Elastomer Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Fluid Compatibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 Control Valve Flow Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 Flow Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 Selection of Flow Characteristic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 Valve Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 Sizing Valves for Liquids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 Abbreviations and Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 Equation Constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 Determining Fp, the Piping Geometry Factor . . . . . . . . . . . . . . . . . . . . . 114 vii
  8. 8. Table of Contents Determining qmax (the Maximum Flow Rate) or DPmax (the Allowable Sizing Pressure Drop) . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 Determining qmax (the Maximum Flow Rate) . . . . . . . . . . . . . . . . . . . . . 115 Determining DPmax (the Allowable Sizing Pressure Drop) . . . . . . . . . . 115 Liquid Sizing Sample Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 Sizing Valves for Compressible Fluids . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 Determining xTP, the Pressure Drop Ratio Factor . . . . . . . . . . . . . . . . . 121 Compressible Fluid Sizing Sample Problem No. 1 . . . . . . . . . . . . . . . . 121 Compressible Fluid Sizing Sample Problem No. 2 . . . . . . . . . . . . . . . . 123 Representative Sizing Coefficients for Single-Ported Globe-Style Valve Bodies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 Representative Sizing Coefficients for Rotary-Shaft Valves . . . . . . . 127 Actuator Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 Globe Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 A. Unbalance Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 Typical Unbalance Areas of Control Valves . . . . . . . . . . . . . . . . 129 B. Force to Provide Seat Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 C. Packing Friction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 Typical Packing Friction Values . . . . . . . . . . . . . . . . . . . . . . . . . . 132 D. Additional Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 Actuator Force Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 Rotary Actuator Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 Torque Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 Breakout Torque . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 Dynamic Torque . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 Typical Rotary Shaft Valve Torque Factors . . . . . . . . . . . . . . . . . . . . . . . . . 134 V-Notch Ball Valve with Composition Seal . . . . . . . . . . . . . . . . . . . . . . . . . 134 High Performance Butterfly Valve with Composition Seal . . . . . . . . . . . . . 134 Maximum Rotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 Non-Destructive Test Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 Magnetic Particle (Surface) Examination . . . . . . . . . . . . . . . . . . . . . . . . 135 Liquid Penetrant (Surface) Examination . . . . . . . . . . . . . . . . . . . . . . . . . 135 Radiographic (Volumetric) Examination . . . . . . . . . . . . . . . . . . . . . . . . . 135 Ultrasonic (Volumetric) Examination . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 Cavitation and Flashing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 Choked Flow Causes Flashing and Cavitation . . . . . . . . . . . . . . . . . . . 136 Valve Selection for Flashing Service . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 Valve Selection for Cavitation Service . . . . . . . . . . . . . . . . . . . . . . . . . . 138 Noise Prediction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 Aerodynamic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 Hydrodynamic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 Noise Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 Noise Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 Packing Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 Packing Selection Guidelines for Sliding−Stem Valves . . . . . . . . . . . . . . . 145 Packing Selection Guidelines for Rotary Valves . . . . . . . . . . . . . . . . . . . . 146Chapter 6. Special Control Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147viii
  9. 9. Table of Contents High Capacity Control Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 Low Flow Control Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 High-Temperature Control Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 Cryogenic Service Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 Customized Characteristics and Noise Abatement Trims . . . . . . . . . . . . . 150 Control Valves for Nuclear Service in the USA . . . . . . . . . . . . . . . . . . . . . . 151 Valves Subject to Sulfide Stress Cracking . . . . . . . . . . . . . . . . . . . . . . . . . 151 Pre-2003 Revisions of MR0175 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 NACE MR0175/ISO 15156 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 NACE MR0103 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153Chapter 7. Steam Conditioning Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 Understanding Desuperheating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 Technical Aspects of Desuperheating . . . . . . . . . . . . . . . . . . . . . . . . . . 156 Typical Desuperheater Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 Fixed Geometry Nozzle Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 Variable Geometry Nozzle Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 Self-Contained Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 Steam Atomized Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 Geometry-Assisted Wafer Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 Understanding Steam Conditioning Valves . . . . . . . . . . . . . . . . . . . . . . . . 161 Steam Conditioning Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 Steam Cooler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 Steam Sparger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 Understanding Turbine Bypass Systems . . . . . . . . . . . . . . . . . . . . . . . . . . 165 Turbine Bypass System Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 Turbine Bypass Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 Turbine Bypass Water Control Valves . . . . . . . . . . . . . . . . . . . . . . . . . . 166 Electro-Hydraulic System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166Chapter 8. Installation and Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 Proper Storage and Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 Proper Installation Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 Read the Instruction Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 Be Sure the Pipeline Is Clean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 Inspect the Control Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 Use Good Piping Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 Control Valve Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 Reactive Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 Preventive Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 Predictive Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 Using Control Valve Diagnostics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 Instrument Air Leakage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 Supply Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 Travel Deviation and Relay Adjustment . . . . . . . . . . . . . . . . . . . . . . . . 171 ix
  10. 10. Table of Contents Instrument Air Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 In-Service Friction and Friction Trending . . . . . . . . . . . . . . . . . . . . . . . 171 Other Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 Continued Diagnostics Development . . . . . . . . . . . . . . . . . . . . . . . . . . 172 Actuator Diaphragm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 Stem Packing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 Seat Rings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 Grinding Metal Seats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 Replacing Seat Rings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 Bench Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174Chapter 9. Standards and Approvals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 Control Valve Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 American Petroleum Institute (API) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 American Society of Mechanical Engineers (ASME) . . . . . . . . . . . . . . 175 European Committee for Standardization (CEN) . . . . . . . . . . . . . . . . . 176 European Industrial Valve Standards . . . . . . . . . . . . . . . . . . . . . . . . 176 European Material Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 European Flange Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 Fluid Controls Institute (FCI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 Instrument Society of America (ISA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 International Electrotechnical Commission (IEC) . . . . . . . . . . . . . . . . . 177 International Standards Organization (ISO) . . . . . . . . . . . . . . . . . . . . . . 178 Manufacturers Standardization Society (MSS) . . . . . . . . . . . . . . . . . . . 178 NACE International . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 Product Approvals for Hazardous (Classified) Locations . . . . . . . . . . . . . 178 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 Canadian Standards Association (CSA) Standards . . . . . . . . . . . . 178 European Committee for Electrotechnical Standardization (CENELEC) Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 Instrument Society of America (ISA) Standards . . . . . . . . . . . . . . . . 178 International Electrotechnical Commission (IEC) Standards . . . . . 178 National Electrical Manufacturer’s Association (NEMA) Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 National Fire Protection Association (NFPA) Standards . . . . . . . . . 179 North American Approvals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 Approval Agencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 Types of Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 Hazardous Location Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 Temperature Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180 NEMA Enclosure Rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 General Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 Hazardous (Classified) Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 CSA Enclosure Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 Intrinsically Safe Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182x
  11. 11. Table of Contents Entity Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 CSA System Parameter Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 Loop Schematic (Control Drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 Comparison of Protection Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . 183 Explosion-proof Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 Advantages of this Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 Disadvantages of this Technique . . . . . . . . . . . . . . . . . . . . . . . . . 184 Installation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 Intrinsically Safe Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 Advantages of this Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 Disadvantages of this Technique . . . . . . . . . . . . . . . . . . . . . . . . . 184 Dust Ignition−proof Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 Non-Incendive Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 Advantages of this Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 Disadvantages of this Technique . . . . . . . . . . . . . . . . . . . . . . . . . 185 European and Asia/Pacific Approvals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 Approval Agencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 CENELEC Approvals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 Types of Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 Flameproof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 Increased Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 Intrinsically Safe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 Non-Incendive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 Hazardous Location Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 Temperature Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 IEC Enclosure Rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 NEMA and IEC Enclosure Rating Comparison . . . . . . . . . . . . . . . . . . . 188 Comparison of Protection Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . 188 Flameproof Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 Advantages of this Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 Disadvantages of this Technique . . . . . . . . . . . . . . . . . . . . . . . . . 188 Increased Safety Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 Advantages of this Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 Disadvantages of this Technique . . . . . . . . . . . . . . . . . . . . . . . . . 189 Intrinsically Safe Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 Advantages of this Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 Disadvantages of this Technique . . . . . . . . . . . . . . . . . . . . . . . . . 189 Type n Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 Advantages of this Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 Disadvantages of this Technique . . . . . . . . . . . . . . . . . . . . . . . . . 189Chapter 10. Engineering Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 Standard Specifications For Valve Materials . . . . . . . . . . . . . . . . . . . . . . . 191 xi
  12. 12. Table of Contents Valve Materials Properties for Pressure−Containing Components . . . . . 197 Physical Constants of Hydrocarbons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 Specific Heat Ratio (K) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202 Physical Constants of Various Fluids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203 Refrigerant 717 (Ammonia) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206 Properties of Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211 Properties of Saturated Steam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212 Properties of Superheated Steam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219 Velocity of Liquids in Pipe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226 Flow of Water Through Schedule 40 Steel Pipe . . . . . . . . . . . . . . . . . . . 228 Flow of Air Through Schedule 40 Steel Pipe . . . . . . . . . . . . . . . . . . . . . . 232 Calculations for Pipe Other than Schedule 40 . . . . . . . . . . . . . . . . . . . . . . 236Chapter 11. Pipe Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 Pipe Engagement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 Carbon and Alloy Steel − Stainless Steel . . . . . . . . . . . . . . . . . . . . . . . . . . 238 American Pipe Flange Dimensions − Diameter of Bolt Circle-Inches . . 251 American Pipe Flange Dimensions − Number of Stud Bolts and Diameter in Inches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252 American Pipe Flange Dimensions − Flange Diameter−Inches . . . . . . . . 253 American Pipe Flange Dimensions − Flange Thickness for Flange Fittings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254 Cast Steel Flange Standard for PN 16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255 Cast Steel Flange Standard for PN 25 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 Cast Steel Flange Standard for PN 40 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257 Cast Steel Flange Standard for PN 63 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258 Cast Steel Flange Standard for PN 100 . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 Cast Steel Flange Standard for PN 160 . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 Cast Steel Flange Standard for PN 250 . . . . . . . . . . . . . . . . . . . . . . . . . . . 260 Cast Steel Flange Standard for PN 320 . . . . . . . . . . . . . . . . . . . . . . . . . . . 260 Cast Steel Flange Standard for PN 400 . . . . . . . . . . . . . . . . . . . . . . . . . . . 261Chapter 12. Conversions and Equivalents . . . . . . . . . . . . . . . . . . . . . . . . . 263 Length Equivalents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263 Whole Inch−Millimeter Equivalents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263 Fractional Inches To Millimeters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264 Additional Fractional/Decimal Inch−Millimeter Equivalents . . . . . . . . . . . . 264 Area Equivalents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266 Volume Equivalents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266 Volume Rate Equivalents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266 Mass Conversion—Pounds to Kilograms . . . . . . . . . . . . . . . . . . . . . . . . . . 267 Pressure Equivalents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 Pressure Conversion—Pounds per Square Inch to Bar . . . . . . . . . . . . . . 268 Temperature Conversion Formulas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269 Temperature Conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269 A.P.I. and Baumé Gravity Tables and Weight Factors . . . . . . . . . . . . . . . 271xii
  13. 13. Table of Contents Equivalent Volume and Weight Flow Rates of Compressible Fluids . . . . 273 Viscosity Conversion Nomograph . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274 Other Useful Conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 Metric Prefixes and Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275Subject Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 xiii
  14. 14. Table of Contentsxiv
  15. 15. Chapter 1 Introduction to Control ValvesWhat Is A Control Valve? cides what must be done to get the process variable back to where itProcess plants consist of hundreds, or should be after a load disturbance oc-even thousands, of control loops all curs. When all the measuring,networked together to produce a prod- comparing, and calculating are done,uct to be offered for sale. Each of some type of final control elementthese control loops is designed to must implement the strategy selectedkeep some important process variable by the controller.such as pressure, flow, level, temper-ature, etc. within a required operating The most common final control ele-range to ensure the quality of the end ment in the process control industriesproduct. Each of these loops receives is the control valve. The control valveand internally creates disturbances manipulates a flowing fluid, such asthat detrimentally affect the process gas, steam, water, or chemical com-variable, and interaction from other pounds, to compensate for the loadloops in the network provides distur- disturbance and keep the regulatedbances that influence the process process variable as close as possiblevariable. to the desired set point. Many people who talk about controlTo reduce the effect of these load dis- valves or valves are really referring toturbances, sensors and transmitters a control valve assembly. The controlcollect information about the process valve assembly typically consists ofvariable and its relationship to some the valve body, the internal trim parts,desired set point. A controller then an actuator to provide the motive pow-processes this information and de- er to operate the valve, and a variety 1
  16. 16. Chapter 1. Introduction to Control Valvesof additional valve accessories, which Actuator Assembly: An actuator,can include positioners, transducers, including all the pertinent accessoriessupply pressure regulators, manual that make it a complete operating unit.operators, snubbers, or limit switches.Other chapters of this handbook sup- Backlash: The general name givenply more detail about each of these to a form of dead band that resultscontrol valve assembly components. from a temporary discontinuity be- tween the input and output of a deviceWhether it is called a valve, control when the input of the device changesvalve or a control valve assembly is direction. Slack, or looseness of a me-not as important as recognizing that chanical connection is a typical exam-the control valve is a critical part of the ple.control loop. It is not accurate to say Capacity* (Valve): The rate of flowthat the control valve is the most im- through a valve under stated condi-portant part of the loop. It is useful to tions.think of a control loop as an instru-mentation chain. Like any other chain, Closed Loop: The interconnectionthe whole chain is only as good as its of process control components suchweakest link. It is important to ensure that information regarding the processthat the control valve is not the weak- variable is continuously fed back toest link. the controller set point to provide con- tinuous, automatic corrections to theFollowing are definitions for process process variable.control, sliding-stem control valve, Controller: A device that operatesrotary-shaft control valve, and other automatically by use of some estab-control valve functions and character- lished algorithm to regulate a con-istics terminology. trolled variable. The controller input receives information about the status of the process variable and then pro- NOTE: vides an appropriate output signal to the final control element. Definitions with an as- terisk (*) are from the Control Loop: (See Closed Loop.) ISA Control Valve Ter- minology standard Control Range: The range of valve S75.05, used with per- travel over which a control valve can mission. maintain the installed valve gain be- tween the normalized values of 0.5 and 2.0.Process Control Control Valve: (See Control Valve Assembly.)Terminology Control Valve Assembly: IncludesAccessory: A device that is all components normally mounted onmounted on the actuator to comple- the valve: the valve body assembly,ment the actuator’s function and make actuator, positioner, air sets, transduc-it a complete operating unit. Examples ers, limit switches, etc.include positioners, supply pressureregulators, solenoids, and limit Dead Band: The range throughswitches. which an input signal can be varied, upon reversal of direction, without ini-Actuator*: A pneumatic, hydraulic, tiating an observable change in theor electrically powered device that output signal. Dead band is the namesupplies force and motion to open or given to a general phenomenon thatclose a valve. can apply to any device. For the valve2
  17. 17. Chapter 1. Introduction to Control Valves vice, the most common final control element in the process control indus- tries is the control valve assembly. The control valve manipulates a flow- ing fluid, such as gasses, steam, wa- ter, or chemical compounds, to com- pensate for the load disturbance and keep the regulated process variable as close as possible to the desired set point.A7152 / IL First-Order: A term that refers to the Figure 1-1. Process Dead Band dynamic relationship between the in- put and output of a device. A first-or- der system or device is one that has only one energy storage device and assembly, the controller output (CO) is whose dynamic transient relationship the input to the valve assembly and between the input and output is char- the process variable (PV) is the output acterized by an exponential behavior. as shown in figure 1-1. When the term Friction: A force that tends to op- Dead Band is used, it is essential that pose the relative motion between two both the input and output variables surfaces that are in contact with each are identified, and that any tests to other. The friction force is a function of measure dead band be under fully the normal force holding these two loaded conditions. Dead band is typi- surfaces together and the characteris- cally expressed as a percent of the tic nature of the two surfaces. Friction input span. has two components: static friction Dead Time: The time interval (Td) in and dynamic friction. Static friction is which no response of the system is the force that must be overcome be- detected following a small (usually fore there is any relative motion be- 0.25% - 5%) step input. It is measured tween the two surfaces. Once relative from the time the step input is initiated movement has begun, dynamic fric- to the first detectable response of the tion is the force that must be over- system being tested. Dead Time can come to maintain the relative motion. apply to a valve assembly or to the Running or sliding friction are colloqui- entire process. (See T63.) al terms that are sometimes used to describe dynamic friction. Stick/slip or Disk: A valve trim element used to “stiction” are colloquial terms that are modulate the flow rate with either lin- sometimes used to describe static fric- ear or rotary motion. Can also be re- tion. Static friction is one of the major ferred to as a valve plug or closure causes of dead band in a valve as- member. sembly. Equal Percentage Characteristic*: Gain: An all-purpose term that can An inherent flow characteristic that, for be used in many situations. In its most equal increments of rated travel, will general sense, gain is the ratio of the ideally give equal percentage changes magnitude of the output change of a of the flow coefficient (Cv) (figure 1-2). given system or device to the magni- tude of the input change that caused Final Control Element: The device the output change. Gain has two com- that implements the control strategy ponents: static gain and dynamic determined by the output of the con- gain. Static gain is the gain relation- troller. While the final control element ship between the input and output and can be a damper, a variable speed is an indicator of the ease with which drive pump, or an on-off switching de- the input can initiate a change in the 3
  18. 18. Chapter 1. Introduction to Control Valves are named Linear, Equal-Percentage, and Quick Opening (figure 1-2). Inherent Valve Gain: The magni- tude ratio of the change in flow through the valve to the change in valve travel under conditions of constant pressure drop. Inherent valve gain is an inherent function of the valve design. It is equal to the slope of the inherent characteristic curve at any travel point and is a func- tion of valve travel. A3449/IL Installed Characteristic*: The rela- tionship between the flow rate and the closure member (disk) travel as it is Figure 1-2. Inherent Valve moved from the closed position to Characteristics rated travel as the pressure drop across the valve is influenced by the varying process conditions. (Seeoutput when the system or device is in Valve Type and Characterization ina steady-state condition. Sensitivity is Chapter 2 for more details on how thesometimes used to mean static gain. installed characteristic is determined.)Dynamic gain is the gain relationshipbetween the input and output when Installed Valve Gain: The magni-the system is in a state of movement tude ratio of the change in flowor flux. Dynamic gain is a function of through the valve to the change infrequency or rate of change of the in- valve travel under actual process con-put. ditions. Installed valve gain is the valve gain relationship that occursHysteresis*: The maximum differ- when the valve is installed in a specif-ence in output value for any single in- ic system and the pressure drop is al-put value during a calibration cycle, lowed to change naturally accordingexcluding errors due to dead band. to the dictates of the overall system. The installed valve gain is equal to theInherent Characteristic*: The rela- slope of the installed characteristictionship between the flow coefficient curve, and is a function of valve travel.and the closure member (disk) travel (See Valve Type and Characterizationas it is moved from the closed position in Chapter 2 for more details on howto rated travel with constant pressure the installed gain is determined.)drop across the valve. I/P: Shorthand for current-to-pres-Typically these characteristics are sure (I-to-P). Typically applied to inputplotted on a curve where the horizon- transducer modules.tal axis is labeled in percent travel and Linearity*: The closeness to which athe vertical axis is labeled as percent curve relating to two variables approx-flow (or Cv) (figure 1-2). Because imates a straight line. (Linearity alsovalve flow is a function of both the means that the same straight line willvalve travel and the pressure drop apply for both upscale and downscaleacross the valve, conducting flow directions. Thus, dead band as de-characteristic tests at a constant pres- fined above, would typically be con-sure drop provides a systematic way sidered a non-linearity.)of comparing one valve characteristicdesign to another. Typical valve char- Linear Characteristic*: An inherentacteristics conducted in this manner flow characteristic that can be repre-4
  19. 19. Chapter 1. Introduction to Control Valvessented by a straight line on a rectan- Process Variability: A precise statis-gular plot of flow coefficient (Cv) ver- tical measure of how tightly the pro-sus rated travel. Therefore equal cess is being controlled about the setincrements of travel provide equal in- point. Process variability is defined increments of flow coefficient, Cv (figure percent as typically (2s/m), where m is1-2). the set point or mean value of the measured process variable and s isLoop: (See Closed Loop.) the standard deviation of the process variable.Loop Gain: The combined gain of allthe components in the loop when Quick Opening Characteristic*: Anviewed in series around the loop. inherent flow characteristic in which aSometimes referred to as open-loop maximum flow coefficient is achievedgain. It must be clearly specified with minimal closure member travelwhether referring to the static loop (figure 1-2).gain or the dynamic loop gain at somefrequency. Relay: A device that acts as a power amplifier. It takes an electrical, pneu-Manual Control: (See Open Loop.) matic, or mechanical input signal and produces an output of a large volumeOpen Loop: The condition where flow of air or hydraulic fluid to the ac-the interconnection of process control tuator. The relay can be an internalcomponents is interrupted such that component of the positioner or a sep-information from the process variable arate valve accessory.is no longer fed back to the controllerset point so that corrections to the Resolution: The minimum possibleprocess variable are no longer pro- change in input required to produce avided. This is typically accomplished detectable change in the output whenby placing the controller in the manual no reversal of the input takes place.operating position. Resolution is typically expressed as aPacking: A part of the valve assem- percent of the input span.bly used to seal against leakagearound the valve disk or stem. Response Time: Usually measured by a parameter that includes bothPositioner*: A position controller dead time and time constant. (See(servomechanism) that is mechanical- T63, Dead Time, and Time Constant.)ly connected to a moving part of a fi- When applied to the valve, it includesnal control element or its actuator and the entire valve assembly.that automatically adjusts its output tothe actuator to maintain a desired Second-Order: A term that refers toposition in proportion to the input sig- the dynamic relationship between thenal. input and output of a device. A sec- ond-order system or device is one thatProcess: All the combined elements has two energy storage devices thatin the control loop, except the control- can transfer kinetic and potential ener-ler. The process typically includes the gy back and forth between them-control valve assembly, the pressure selves, thus introducing the possibilityvessel or heat exchanger that is being of oscillatory behavior and overshoot.controlled, as well as sensors, pumps,and transmitters. Sensor: A device that senses the value of the process variable and pro-Process Gain: The ratio of the vides a corresponding output signal tochange in the controlled process vari- a transmitter. The sensor can be anable to a corresponding change in the integral part of the transmitter, or itoutput of the controller. may be a separate component. 5
  20. 20. Chapter 1. Introduction to Control ValvesSet Point: A reference value repre- Travel*: The movement of the closuresenting the desired value of the pro- member from the closed position to ancess variable being controlled. intermediate or rated full open posi- tion.Shaft Wind-Up: A phenomenonwhere one end of a valve shaft turns Travel Indicator: A pointer and scaleand the other does not. This typically used to externally show the position ofoccurs in rotary-style valves where the the closure member typically withactuator is connected to the valve clo- units of opening percent of travel orsure member by a relatively long degrees of rotation.shaft. While seal friction in the valve Trim*: The internal components of aholds one end of the shaft in place, valve that modulate the flow of therotation of the shaft at the actuator controlled fluid.end is absorbed by twisting of theshaft until the actuator input transmits Valve: (See Control Valve Assembly.)enough force to overcome the friction. Volume Booster: A stand-aloneSizing (Valve): A systematic proce- relay is often referred to as a volumedure designed to ensure the correct booster or simply booster because itvalve capacity for a set of specified boosts, or amplifies, the volume of airprocess conditions. supplied to the actuator. (See Relay.)Stiction: (See Friction.) Sliding-Stem ControlT63 (Tee-63): A measure of device Valve Terminologyresponse. It is measured by applying The following terminology applies toa small (usually 1-5%) step input to the physical and operating character-the system. T63 is measured from the istics of standard sliding-stem controltime the step input is initiated to the valves with diaphragm or piston ac-time when the system output reaches tuators. Some of the terms, particular-63% of the final steady-state value. It ly those pertaining to actuators, areis the combined total of the system also appropriate for rotary-shaft con-Dead Time (Td) and the system Time trol valves. Many of the definitionsConstant (t). (See Dead Time and presented are in accordance with ISATime Constant.) S75.05, Control Valve Terminology,Time Constant: A time parameter although other popular terms are alsothat normally applies to a first-order included. Additional explanation iselement. It is the time interval mea- provided for some of the more com-sured from the first detectable re- plex terms. Component part namessponse of the system to a small (usu- are called out on accompanying fig-ally 0.25% - 5%) step input until the ures 1-3 through 1-6. Separate sec-system output reaches 63% of its final tions follow that define specificsteady-state value. (See T63.) When rotary-shaft control valve terminology,applied to an open-loop process, the control valve functions and character-time constant is usually designated as istics terminology, and other process control terminology.t (Tau). When applied to a closed-loopsystem, the time constant is usually Actuator Spring: A spring, or groupdesignated as λ (Lambda). of springs, enclosed in the yoke or ac- tuator casing that moves the actuatorTransmitter: A device that senses stem in a direction opposite to thatthe value of the process variable and created by diaphragm pressure.transmits a corresponding output sig-nal to the controller for comparison Actuator Stem: The part that con-with the set point. nects the actuator to the valve stem6
  21. 21. Chapter 1. Introduction to Control Valves LOADING PRESSURE CONNECTION DIAPHRAGM CASING DIAPHRAGM AND STEM SHOWN IN UP POSITION DIAPHRAGM PLATE ACTUATOR SPRING DIRECT-ACTING ACTUATOR STEM ACTUATOR SPRING SEAT SPRING ADJUSTOR STEM CONNECTOR YOKE TRAVEL INDICATOR INDICATOR SCALE W0363-1 COMPACT FIELD-REVERSIBLE MULTI-SPRING ACTUATOR INTEGRAL PNEUMATIC PASSAGEWAYS INTEGRATED POSITIONER MOUNTING NAMUR POSITIONER AIR-TO-OPEN MOUNTING CAPABILITY VALVE ASSEMBLY ONE-PIECE SCREWED PACKING FOLLOWER STANDARD LIVE-LOADED PACKING CLAMPED BONNET DESIGN W8486-3 BONNET GASKET VALVE PLUG STEM PACKING FLANGE SPIRAL ACTUATOR YOKE LOCKNUT WOUND PUSH-DOWN- GASKET PACKING PACKING BOX TO-CLOSE VALVE BODY BONNET ASSEMBLY CAGE GASKET VALVE PLUG CAGE SEAT SEAT RING GASKET RING W0989 VALVE BODYFigure 1-3. Major Components of Typical Sliding-Stem Control Valve Assemblies 7
  22. 22. Chapter 1. Introduction to Control Valves DIAPHRAGM CASINGS DIAPHRAGM AND STEM SHOWN IN DOWN POSITION DIAPHRAGM PLATE LOADING PRESSURE CONNECTION ACTUATOR SPRING ACTUATOR STEM SPRING SEAT SPRING ADJUSTOR STEM CONNECTOR YOKE TRAVEL INDICATOR INDICATOR SCALE W0364-1/IL Figure 1-4. Typical Reverse-Acting Diaphragm Actuator W0667/IL W6434/IL Figure 1-5. Extension Bonnet Figure 1-6. Bellows Seal Bonnetand transmits motion (force) from the motion to the valve positioner (figureactuator to the valve. 1-7).Actuator Stem Extension: An ex- Actuator Stem Force: The net forcetension of the piston actuator stem to from an actuator that is available forprovide a means of transmitting piston actual positioning of the valve plug.8
  23. 23. Chapter 1. Introduction to Control ValvesACTUATOR STEM CYLINDERPISTON SEAL PISTON ACTUATOR STEM SEAL CYLINDER CYLINDER SEAL CLOSURE SEAL TRAVEL SEAL BUSHING INDICATOR SCALEYOKE STEM CONNECTORTRAVEL INDICATOR W7447-1/IIL Figure 1-7. Typical Double-Acting Piston Actuator with Bias SpringAngle Valve: A valve design in which Bonnet Assembly: (Commonly Bon-one port is co-linear with the valve net, more properly Bonnet Assembly):stem or actuator, and the other port is An assembly including the partat a right angle to the valve stem. through which a valve stem moves(See also Globe Valve.) and a means for sealing against leak- age along the stem. It usually pro-Bellows Seal Bonnet: A bonnet that vides a means for mounting the actua-uses a bellows for sealing against tor and loading the packing assembly.leakage around the closure member Bottom Flange: A part that closes astem (figure 1-6). valve body opening opposite the bon- net opening. It can include a guideBonnet: The portion of the valve that bushing and/or serve to allow reversalcontains the packing box and stem of the valve action.seal and can guide the stem. It pro-vides the principal opening to the Bushing: A device that supports and/body cavity for assembly of internal or guides moving parts such as valveparts or it can be an integral part of stems.the valve body. It can also provide forthe attachment of the actuator to the Cage: A part of a valve trim that sur-valve body. Typical bonnets are rounds the closure member and canbolted, threaded, welded, provide flow characterization and/or apressure-seals, or integral with the seating surface. It also provides stabil-body. (This term is often used in refer- ity, guiding, balance, and alignment,ring to the bonnet and its included and facilitates assembly of other partspacking parts. More properly, this of the valve trim. The walls of thegroup of component parts should be cage contain openings that usuallycalled the bonnet assembly.) determine the flow characteristic of 9
  24. 24. Chapter 1. Introduction to Control Valves W0957/IL W0958/IL W0959/IL QUICK OPENING LINEAR EQUAL PERCENTAGE Figure 1-8. Characterized Cages for Globe-Style Valve Bodiesthe control valve. Various cage styles Diaphragm Plate: A plate concentricare shown in figure 1-8. with the diaphragm for transmitting force to the actuator stem.Closure Member: The movable part Direct Actuator: A diaphragm actua-of the valve that is positioned in the tor in which the actuator stem extendsflow path to modify the rate of flow with increasing diaphragm pressure.through the valve. Extension Bonnet: A bonnet withClosure Member Guide: That por- greater dimension between the pack-tion of a closure member that aligns ing box and bonnet flange for hot orits movement in either a cage, seat cold service.ring, bonnet, bottom flange, or anytwo of these. Globe Valve: A valve with a linear motion closure member, one or moreCylinder: The chamber of a piston ports, and a body distinguished by aactuator in which the piston moves globular shaped cavity around the port(figure 1-7). region. Globe valves can be further classified as: two-way single-ported; two-way double-ported (figure 1-9);Cylinder Closure Seal: The sealing angle-style (figure 1-10); three-wayelement at the connection of the pis- (figure 1-11); unbalanced cage-guidedton actuator cylinder to the yoke. (figure 1-3); and balance cage-guided (figure 1-12).Diaphragm: A flexible, pressure re-sponsive element that transmits force Lower Valve Body: A half housingto the diaphragm plate and actuator for internal valve parts having onestem. flow connection. The seat ring is nor- mally clamped between the upperDiaphragm Actuator: A fluid pow- valve body and the lower valve bodyered device in which the fluid acts in split valve constructions.upon a flexible component, the dia- Offset Valve: A valve constructionphragm. having inlet and outlet line connec- tions on different planes but 180 de-Diaphragm Case: A housing, con- grees opposite each other.sisting of top and bottom section,used for supporting a diaphragm and Packing Box (Assembly): The partestablishing one or two pressure of the bonnet assembly used to sealchambers. against leakage around the closure10
  25. 25. Chapter 1. Introduction to Control Valves W0467/IL W0665/IL Figure 1-9. Reverse Double-Ported Figure 1-11. Three-Way Valve with Globe-Style Valve Body Balanced Valve Plug W0992/IL W0971/IL Figure 1-12. Valve Body with Cage-Style Trim, Balanced ValveFigure 1-10. Flanged Angle-Style Con- Plug, and Soft Seat trol Valve Body packing parts are shown in figure 1-13.member stem. Included in the com- Piston: A movable pressure respon-plete packing box assembly are vari- sive element that transmits force toous combinations of some or all of the the piston actuator stem (figure 1-7).following component parts: packing,packing follower, packing nut, lantern Piston Type Actuator: A fluid pow-ring, packing spring, packing flange, ered device in which the fluid actspacking flange studs or bolts, packing upon a movable piston to provide mo-flange nuts, packing ring, packing wip- tion to the actuator stem. Piston typeer ring, felt wiper ring, belleville actuators (figure 1-7) are classified assprings, anti-extrusion ring. Individual either double-acting, so that full power 11
  26. 26. Chapter 1. Introduction to Control Valves12A7837-A 13A9775-E 14A1849-ESTANDARDTFE V-RING GRAPHITE PACKING ARRANGEMENTSB2565 / IL 1 LOCATION OF SACRIFICIAL ZINC WASHER, IF USED. Figure 1-13. Comprehensive Packing Material Arrangements for Globe-Style Valve Bodiescan be developed in either direction, the piston actuator cylinder againstor as spring-fail so that upon loss of leakage. Synthetic rubber O-rings aresupply power, the actuator moves the used in the bushings to seal the cylin-valve in the required direction of trav- der, the actuator stem, and the actua-el. tor stem extension (figure 1-7).Plug: A term frequently used to refer Seat: The area of contact betweento the closure member. the closure member and its mating surface that establishes valve shut-off.Port: The flow control orifice of acontrol valve. Seat Load: The net contact force be- tween the closure member and seatRetaining Ring: A split ring that is with stated static conditions. In prac-used to retain a separable flange on a tice, the selection of an actuator for avalve body. given control valve will be based on how much force is required to over-Reverse Actuator: A diaphragm ac- come static, stem, and dynamic un-tuator in which the actuator stem re- balance with an allowance made fortracts with increasing diaphragm pres- seat load.sure. Reverse actuators have a sealbushing (figure 1-4) installed in the Seat Ring: A part of the valve bodyupper end of the yoke to prevent leak- assembly that provides a seating sur-age of the diaphragm pressure along face for the closure member and canthe actuator stem. provide part of the flow control orifice.Rubber Boot: A protective device to Separable Flange: A flange that fitsprevent entrance of damaging foreign over a valve body flow connection. Itmaterial into the piston actuator seal is generally held in place by means ofbushing. a retaining ring.Seal Bushing: Top and bottom bush- Spring Adjustor: A fitting, usuallyings that provide a means of sealing threaded on the actuator stem or into12
  27. 27. Chapter 1. Introduction to Control Valvesthe yoke, to adjust the spring com- verging or mixing flows), or one inletpression. and two outlets (for diverging or di- verting flows). The term valve body, orSpring Seat: A plate to hold the even just body, frequently is used inspring in position and to provide a flat referring to the valve body togethersurface for the spring adjustor to con- with its bonnet assembly and includedtact. trim parts. More properly, this group of components should be called theStatic Unbalance: The net force pro- valve body assembly.duced on the valve stem by the fluidpressure acting on the closure mem-ber and stem with the fluid at rest and Valve Body Assembly (Commonlywith stated pressure conditions. Valve Body or Valve, more properly Valve Body Assembly): An assemblyStem Connector: The device that of a valve, bonnet assembly, bottomconnects the actuator stem to the flange (if used), and trim elements.valve stem. The trim includes the closure member, which opens, closes, or partially ob-Trim: The internal components of a structs one or more ports.valve that modulate the flow of thecontrolled fluid. In a globe valve body, Valve Plug: A term frequently inter-trim would typically include closure changed with plug in reference to themember, seat ring, cage, stem, and closure member.stem pin.Trim, Soft-Seated: Valve trim with an Valve Stem: In a linear motion valve,elastomeric, plastic or other readily the part that connects the actuatordeformable material used either in the stem with the closure member.closure component or seat ring to pro-vide tight shutoff with minimal actuator Yoke: The structure that rigidly con-forces. nects the actuator power unit to the valve.Upper Valve Body: A half housingfor internal valve parts and having oneflow connection. It usually includes ameans for sealing against leakage Rotary-Shaft Control Valvealong the stem and provides a means Terminologyfor mounting the actuator on the splitvalve body. The definitions that follow apply spe- cifically to rotary-shaft control valves.Valve Body: The main pressureboundary of the valve that also pro-vides the pipe connecting ends, the Actuator Lever: Arm attached tofluid flow passageway, and supports rotary valve shaft to convert linear ac-the seating surfaces and the valve tuator stem motion to rotary force toclosure member. Among the most position disk or ball of rotary-shaftcommon valve body constructions valve. The lever normally is positivelyare: a) single-ported valve bodies connected to the rotary shaft by closehaving one port and one valve plug; b) tolerance splines or other means todouble-ported valve bodies having minimize play and lost motion.two ports and one valve plug; c)two-way valve bodies having two flow Ball, Full: The flow-controlling mem-connections, one inlet and one outlet; ber of rotary-shaft control valves usingd) three-way valve bodies having a complete sphere with a flow pas-three flow connections, two of which sage through it. The flow passagecan be inlets with one outlet (for con- equals or matches the pipe diameter. 13
  28. 28. Chapter 1. Introduction to Control Valves SEGMENTED BALL VALVE W4920/IL W4641 CONVENTIONAL DISK BUTTERFLY VALVE W6213/IL ECCENTRIC DISK VALVE W5477/IL CONTOURED DISK BUTTERFLY VALVE Figure 1-14. Typical Rotary-Shaft Control Valve Constructions14
  29. 29. Chapter 1. Introduction to Control ValvesBall, Segmented: The flow-control- Flangeless valves are held betweenling member of rotary shaft control ANSI-class flanges by longvalves using a partial sphere with a through-bolts (sometimes also calledflow passage through it. wafer-style valve bodies).Ball, V-notch: The most common Plug, Eccentric: Style of rotary con-type of segmented ball control valve. trol valve with an eccentrically rotatingThe V-notch ball includes a polished plug which cams into and out of theor plated partial-sphere surface that seat, which reduces friction and wear.rotates against the seal ring through- This style of valve has been wellout the travel range. The V-shaped suited for erosive applications.notch in the ball permits wide range-ability and produces an equal percent- Reverse Flow: Flow from the shaftage flow characteristic. side over the back of the disk, ball, or plug. Some rotary-shaft control valves Note: are capable of handling flow equally well in either direction. Other rotary The balls mentioned designs might require modification of above, and the disks actuator linkage to handle reverse which follow, perform a flow. function comparable to the valve plug in a Rod End Bearing: The connection globe-style control often used between actuator stem and valve. That is, as they actuator lever to facilitate conversion rotate they vary the size of linear actuator thrust to rotary force and shape of the flow- with minimum of lost motion. Use of a stream by opening more standard reciprocating actuator on a or less of the seal area rotary-shaft valve body commonly re- to the flowing fluid. quires linkage with two rod end bear- ings. However, selection of an actua-Disk, Conventional: The symmetri- tor specifically designed forcal flow-controlling member used in rotary-shaft valve service requiresthe most common varieties of butterfly only one such bearing and thereby re-rotary valves. High dynamic torques duces lost motion.normally limit conventional disks to 60degrees maximum rotation in throttling Rotary-Shaft Control Valve: A valveservice. style in which the flow closure mem- ber (full ball, partial ball, disk or plug)Disk, Dynamically Designed: A but- is rotated in the flowstream to controlterfly valve disk contoured to reduce the capacity of the valve (figure 1-14).dynamic torque at large increments ofrotation, thereby making it suitable for Seal Ring: The portion of athrottling service with up to 90 de- rotary-shaft control valve assemblygrees of disk rotation. corresponding to the seat ring of a globe valve. Positioning of the disk orDisk, Eccentric: Common name for ball relative to the seal ring deter-valve design in which the positioning mines the flow area and capacity ofof the valve shaft/disk connections the unit at that particular increment ofcauses the disk to take a slightly ec- rotational travel. As indicated above,centric path on opening. This allows some seal ring designs permit bi-di-the disk to be swung out of contact rectional flow.with the seal as soon as it is opened,thereby reducing friction and wear. Shaft: The portion of a rotary-shaft control valve assembly correspondingFlangeless Valve: Valve style com- to the valve stem of a globe valve.mon to rotary-shaft control valves. Rotation of the shaft positions the disk 15

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