ABSTRACT
Introduction 1050 Orientation Table 1051
Control Valve Trends 1051 Globe vs. Rotary Valves 1051 Valves vs. Other Final Control Elements 1051
Control Valve Sizing 1051 Collecting the Process Data 1053 Determining the Valve Pressure Drop 1053
Characteristics, Gain, and Rangeability 1054 Characteristics and Gain 1054 Valve Rangeability 1057
Actuator Selection 1058 Piston Actuators 1058 Actuator Speeds of Response 1059 Actuator Power 1059 Valve Failure Position 1059
Positioners 1060 When to Use Positioners 1060 When Not to Use Positioners 1060 Positioners to Eliminate Dead Band 1061 Split-Range Operation 1061 Accessories 1061
Process Application Considerations 1061 Pressure Considerations 1061 High-Temperature Service 1063 Low-Temperature Service 1066 Cavitation and Erosion 1068 Methods to Eliminate Cavitation 1068 Control Valve Noise 1072
Flashing and Erosion 1073 Corrosion 1075 Viscous and Slurry Service 1075 Valves That Can Be Sterilized 1076 Valve Leakage 1076
Installation 1080 Climate and Atmospheric Corrosion 1080
Control Valve Specification Form 1080 References 1080 Bibliography 1085
6.2 ACCESSORIES AND POSITIONERS 1087
Introduction 1089 Smart Valves 1089 Positioners 1090
When to Use Positioners 1091 When Not to Use a Positioner 1093 Positioner Performance 1093 Positioner Designs 1094 Positioner Accessories 1095 Position Indicators 1095
Transducers 1096 I/P (Electropneumatic) Transducers 1096 Digital Electropneumatic Transducers 1096
Relays 1096 Booster Relays 1096 Reversing and Other Relays 1097 Quick-Exhaust Relays 1098 Relays to Lock-up Valve Position 1099 Failure Position Guaranteed by Stored Air 1100
Energy Supplies 1100 Air Sets 1100 Hydraulic (High-Pressure) Operation 1101 Hydraulic (Water) Operation 1101
Limit Switches 1101 Solenoid Valves 1101
Three-Way Solenoids 1101 Four-Way Solenoids 1102 Solenoid Capacity 1102
Handwheels 1102 Limit Stops 1103 Bypass Valve 1103 References 1104 Bibliography 1104
6.3 ACTUATORS: DIGITAL, ELECTRIC, HYDRAULIC, SOLENOID 1105
Introduction 1107 Selection and Application 1107
Actuator Types 1107 Actuator Features 1107
Digital Valve Actuators 1109 Electromechanical Actuators 1110
Reversible Motor Gear Actuators 1111 Rotary Output Actuators 1111 Linear Output Actuators 1112
Electrohydraulic Actuators 1114 External Hydraulic Source 1114 Hermetically Sealed Power Pack 1114 Motor and Pump Combinations 1115
Solenoid Valves 1118 Modulating Solenoid Valves 1120
Smart Actuators 1121 Applications 1121
References 1122 Bibliography 1123
6.4 ACTUATORS: PNEUMATIC 1124
Introduction 1126 Definitions 1126 Actuator Features and Selection 1126 Spring/Diaphragm Actuators 1126
Steady-State Force Balance 1127 Actuator Sizing Example 1128 Actuator Nonlinearities 1129 Dynamic Performance of Actuators 1129 Safe Failure Position 1131 Pneumatic Response Times 1132
Piston Actuators 1133 High-Speed Actuators 1133 Relative Merits of Diaphragm
and Piston Actuators 1135
Rotary Valve Actuators 1136 Cylinder Type 1137 Rotation by Spline or Helix 1138 Vane Type 1138 Rotary Pneumatic Actuators 1138
Other Pneumatic Actuators 1139 Pneumohydraulic Actuators 1139 Electropneumatic Actuators 1140
Reliability 1141 Conclusions 1142 References 1142 Bibliography 1143
6.5 ADVANCED STEM PACKING DESIGNS 1144
Introduction 1144 History 1144
Bibliography 1149
6.6 CAPACITY TESTING 1150
Introduction 1150 1. Scope 1150 2. Purpose 1150 3. Nomenclature 1150 4. Test System 1150
4.1 General Description 1150 4.2 Test Specimen 1150 4.3 Test Section 1152 4.4 Throttling Valves 1152 4.5 Flow Measurement 1152 4.6 Pressure Taps 1152 4.7 Pressure Measurement 1153 4.8 Temperature Measurement 1153 4.9 Installation of Test Specimen 1153 4.10 Accuracy of Test 1153
5. Test Fluids 1153 5.1 Incompressible Fluids 1153 5.2 Compressible Fluids 1153
Summary 1153
6.7 CHARACTERISTICS AND RANGEABILITY 1154
Introduction 1154 Valve Gain and Loop Gain 1154
Nonlinear Processes 1154 Installed Valve Gain 1155
Theoretical Valve Characteristics 1155 Valve Testing 1155 Valve Characteristics 1155 Valve and Process Characteristics 1155 Selection Recommendations 1156 Installation Causes Distortion 1157 Distortion Coefficient 1157 Correcting the Valve Characteristic 1158
Rangeability 1158 Improved Definition of Rangeability 1159 Why Traditional Rangeability Is Wrong 1159
Conclusions 1160 Bibliography 1160
6.8 DIAGNOSTICS AND PREDICTIVE VALVE MAINTENANCE 1161
Introduction 1161 Diagnostics 1161
Instrumentation Used 1161 Diagnostic Methods 1162 Characteristics Tests 1162 Valve Signatures 1162 Analyzing Valve Signatures 1164
Conclusions 1164 Bibliography 1164
6.9 DYNAMIC PERFORMANCE OF CONTROL VALVES 1165
Valve Response 1165 Definitions 1165
Discussion 1166 Valve System 1166 Install Positioner 1167 Increase Force 1168 Reduce Friction 1168 Defining Response 1168 Measuring Response 1168 Relationships 1169 Determine Required Response
Specifications 1169 Application Examples 1169 Flow Control 1169 Reactor Mixing 1170 Neutralizing Waste Water 1170 Antisurge Valve 1170 Delay or Slowdown Valve Action 1170 Safety Solenoid Valves 1170 Troubleshoot Valve Response 1171
Bibliography 1171 References 1171
6.10 EMERGENCY PARTIAL-STROKE TESTING OF BLOCK VALVES 1172
Introduction 1172 The Partial-Stroke Test 1172
Mechanical Limiting 1173 Position Control 1173 Solenoid Valve 1173
Impact of PST on SIL 1173 Block Valve Analysis 1175
Overall SIS Performance 1178 Single Block Valve Case 1178 Dual Block Valve Case 1179
Conclusions 1181 Bibliography 1181
6.11 FIELDBUS AND SMART VALVES 1182
Introduction 1182 Benefits and Savings 1183
Hart, Foundation Fieldbus, and Profibus-PA 1183
Valve Calibration and Configuration 1185 Safety and Pollution 1188 On-line Plant Asset Management 1189
Digital Valve Instrumentation 1189 Second Generation 1189
Conclusions 1192 References 1192
6.12 INTELLIGENT VALVES, POSITIONERS, ACCESSORIES 1193
Introduction 1193 Advantages of Intelligent Positioners 1193 Typical Performance Specifications 1194 Generating the Pneumatic Output 1194 Valve Performance Monitoring 1195
Controlling the Process 1195 Changing the Valve’s Characteristics 1195
Operation of Smart Positioners 1196 Maintenance and Calibration 1197
Accessories 1197 Flow Control by Smart Valve 1197
Limitations 1198 References 1198 Bibliography 1198
6.13 MISCELLANEOUS VALVE AND TRIM DESIGNS 1199
Introduction 1200 Miscellaneous Valve Designs 1200
Dynamically Balanced Plug Valves 1200 Positioned Plug In-Line Valves 1201 Expansible Valve Designs 1202 Fluid Interaction Valves 1205
Special Valve Application 1206 Cavitation and Flashing 1206 Dirty Process Services 1208 High Noise 1209 High-Capacity Valves 1210
Cryogenic Valves 1210 High-Temperature Valves 1210 Steam Conditioning Valves 1211 Tank-Mounted Valves 1211
Bibliography 1211
6.14 VALVES: NOISE CALCULATION, PREDICTION, AND REDUCTION 1213
Introduction 1213 Sound and Noise 1214
Speed of Sound 1214 The Human Ear 1214
Loudness Perception 1215 Limiting Valve Noise 1215
Valve Noise 1216 Control Element Instability 1217 Resonant Vibration 1217 Hydrodynamic Noise 1218 Aerodynamic Noise 1218
Controlling Noise 1218 Path Treatment 1219 Source Treatment 1220
Aerodynamic Noise Prediction 1223 Standards 1224 Calculations 1224 Noise Calculation Example 1230 Applying Distance Corrections 1232
Hydrodynamic Noise Prediction 1232 Bibliography 1233
6.15 SIZING 1234
Introduction 1234 About This Section 1234 Standards 1234
General Principles 1235 The Flow Coefficient 1235
Liquid Sizing 1237 Relative Valve Capacity Coefficient (
C
) 1237 Factors
F
,
F
,
F
, and
F
1237 Example 1241
Units Used in Valve Sizing 1241 Sizing Example for Liquids 1243 The Cavitation Phenomenon 1244 Flashing 1248 Laminar or Viscous Flow 1250
Gas and Vapor Sizing 1252 Equations for Turbulent Flow 1252 Constants for Engineering Units 1253 Expansion Factor (
Y
) 1253 Choked Flow 1253 Velocity of Compressible Fluids 1254 Sizing for Compressible Fluids
(Example 12) 1255
Two-Phase Flow 1256 Liquid-Gas Mixtures 1257 Liquid-Vapor Mixtures 1258
Conclusions 1259 Nomenclature 1259 References 1260 Bibliography 1261
6.16 VALVE TYPES: BALL VALVES 1262
Introduction 1264 Throttling Ball Valves 1264
Conventional Ball Valves 1265 The Valve Trim 1266 Flow Characteristics 1267
Characterized Ball Valves 1268 Construction 1268 Characteristics 1269
Ball and Cage Valves 1269 Sizes and Other Features 1270 Ball Unseated by Stem 1271 Ball Gripped by Cage 1271
References 1271 Bibliography 1271
6.17 VALVE TYPES: BUTTERFLY VALVES 1273
Introduction 1274 Conventional Butterfly Valves 1275
Operation 1276 Construction 1276
High-Performance Butterfly Valves 1276 Tight Shut-off Designs 1278 Leakage Ratings 1279 Fire-Safe Designs 1280
Torque Characteristics 1280 Noise Suppression 1282 Bibliography 1283
6.18 VALVE TYPES: DIGITAL VALVES 1284
Introduction 1284 History 1285
Balanced Piston Digital Control 1285 Top-Entry Design 1285
Flow Metering 1288 Gas Flow 1288 Liquid Flow 1288
Conclusions 1288 Reference 1289 Bibliography 1289
6.19 VALVE TYPES: GLOBE VALVES 1290
Valve Trends 1291 Trim Designs 1292
Trim Flow Characteristics 1294 Rangeability 1295 Standard Trim Configurations 1296 Special Trim Configurations 1296 Trim Materials 1298 Leakage 1298 Plug Stems 1299
Bonnet Designs 1300 Bolted Bonnets 1300 Pressure Seal Bonnets 1301 Bonnet Classification 1302 Bonnet Packing 1303
Body Forms 1308 Double-Ported Valves 1309 Single-Seated Valves 1309 Three-Way Valves 1315 Lined and Thermoplastic Valves 1315
Valve Connections 1316 Flanged Ends 1316 Welded Ends 1317 Threaded Ends 1317 Special End Fittings 1318
Materials of Construction 1318 Trademarks 1321 Reference 1321 Bibliography 1321
6.20 VALVE TYPES: PINCH VALVES 1323
Introduction 1323 The Sleeve 1326 Pinch Valve Types 1328
Pressure Limitations 1328 Shell and Tube Design 1328 Throttling Characteristics 1334
Applications 1336 Wastewater 1336 Flue-Gas Desulfurization 1337 Mine Slurries 1337 Paper and Tile Manufacturing 1337 Toxic Gas Applications 1337 Pigments, Paint, and Ink 1337 Glue 1337
Food 1337 Powders and Grinding Compounds 1337 Chemicals 1337
Cavitation 1337 The Phenomenon 1338 The Pinch Valves 1338 Limiting or Eliminating the Damage 1338
Conclusions 1340 Bibliography 1340
6.21 VALVE TYPES: PLUG VALVES 1341
General Characterisics 1342 Plug Valve Features 1343 Throttling and Actuator Considerations 1343
Design Variations 1343 Characterized Plug Valves 1344 V-Ported Design 1344 Adjustable Cylinder Type 1345 Semispherical Plugs for Tight Closure 1345 Expanding Seat Plate Design 1345 Retractable Seat Type 1346 Overtravel Seating Design 1346 Multiport Design 1347
Bibliography 1347
6.22 VALVE TYPES: SAUNDERS DIAPHRAGM VALVES 1348
Introduction 1348 Saunders Valve Construction 1348
Materials of Construction 1350 Straight-Through Design 1351 Full Bore Valve 1352 Dual-Range Design 1352
Bibliography 1352
6.23 VALVE TYPES: SLIDING GATE VALVES 1353
Introduction 1354 Sliding Gate Valve Designs 1354
Knife Gate Valves 1354 Positioned-Disc Valves 1355 Plate and Disc Valves 1356
Bibliography 1357
INTRODUCTION
In the field of control valve design, the most important developments of the last decade occurred in the areas of electric and digital actuators (Section 6.3), in valve diagnostics (Section 6.8), dynamic performance evaluation (Section 6.9), safety shutdown systems (Section 6.10), fieldbus interaction (Section 6.11), intelligent positioners (Section 6.12), valve status detection and use for control (Section 6.13), and in the increased availability of special valve designs (Section 6.12). Because each of these topics are covered in the noted separate sections, they are not treated in detail in this section.
