ABSTRACT
Zero-Voltage-Fired SCR Controllers 1371 Controlling Infrared Tungsten Heaters 1372 Common SCR Limitations 1372
Ignitron Tube 1373 Power Amplifier 1374 References 1374 Bibliography 1374
7.3 LINEAR AND ANGULAR POSITIONING OF MACHINERY 1375
Open-and Closed-Loop Positioning 1376 Positioning System Components 1376
Motors and Actuators 1377
Electric Motors 1377 Motor Drivers 1378 Controllers 1378 Sensors for Feedback 1378
Communication Protocols 1380 Conclusions 1380 References 1380 Bibliography 1381
7.4 PUMPS AS CONTROL ELEMENTS 1382
Rotodynamic or Centrifugal Pumps 1384 Radial-Flow 1384 Axial-and Mixed-Flow 1385 Peripheral or Regenerative Turbine 1385
Positive-Displacement Pumps 1386 Rotary Pumps 1386 Gear Pumps 1387 Reciprocating Pumps 1387
Air Pumps and Air Lifts 1388 Condensate Pumps 1388 Air Lifts 1388
Design of Pumping Systems 1388 Head Requirements 1388 NPSH Calculation 1389 Specific Speed 1390 Horsepower 1390 Installation Considerations for Wastewater
Pumping Stations 1390 Metering Pumps 1391
Plunger Pumps 1391 Diaphragm Pumps 1392 Pneumatic Metering Pumps 1393
Installation Considerations 1393 NPSH and Pulsation Dampening 1395
Opposed Centrifugal Pumps 1395 Bibliography 1396
7.5 REGULATORS-FLOW 1397
Introduction 1398 Purge Flow Regulators 1398 Flow Regulators for Chromatographs 1399 Variable-Orifice Flow Regulators 1399
HVAC Balancing Flow Regulators 1399 Oil Flow Regulator 1401 Industrial Flow Regulators 1401
Thermal Mass Flowmeters 1402 Bibliography 1403
7.6 REGULATORS-LEVEL 1405
Introduction 1405 Float-Type Level Regulators 1405
The Phenomenon of Offset 1406 Span, Dead Band, and Hysteresis 1406 Power Generated by the Float 1406 Specific Gravity and Temperature Effects 1407 Stuffing Boxes 1408 Installation 1408 Conclusions 1409
Diverter Valves 1409 Altitude Valves 1410 Bibliography 1411
7.7 REGULATORS-PRESSURE 1412
Introduction 1413 Regulators vs. Control Valves 1414
Control Valves 1414 Regulator Applications 1414
Gas Industry Applications 1415 Liquid Pressure Regulation 1415 Gas Station Safety Regulators 1416 Pressure Surge Relief Valves 1416
Pressure Regulator Designs 1416 Weight-Loaded Regulators 1418 Spring-Loaded Regulators 1418 Pilot-Operated Regulators 1418
Regulator Characteristics and Sizing 1419 Seating and Sensitivity 1419 Droop or Offset 1420 Noise 1421 Cavitation 1422 Sizing and Rangeability 1422
Stability 1422 Safety 1423 Installation 1423
Bibliography 1423 ISA Specification Form (Table 7.7s) 1425 Instructions for ISA Form S20.51 1425
7.8 REGULATORS-TEMPERATURE 1426
Introduction 1427 Control Quality 1427
Types of Temperature Regulators 1428 Direct-and Pilot-Actuated 1428 Remote or Internal Element 1428 Accessories and Special Features 1429
Thermal Systems 1430 Bulbs, Wells, Fittings 1430 Vapor-Filled System 1431 Liquid-Filled System 1434 Hot Chamber System 1435 Fusion-Type System (Wax-Filled) 1435
The Regulator Valve 1436 Single-and Double-Seated Valves 1436 Three-Way Valves 1436 Valve Features 1438
Conclusions 1438 Bibliography 1438
7.9 THERMOSTATS AND HUMIDISTATS 1440
Introduction 1441 Accuracy of Thermostats and Humidistats 1441
Conventional 1441 Advanced 1441
Thermostats 1441 ElectroMechanical Designs 1442 Electrical/Electronic Design Features 1442 Microprocessor-Based Units 1443 Control by Phone 1443 The Proportional-Only Controller 1443 Thermostat Action and Spring Range 1445 Thermostat Design Variations 1445 Special-Purpose Thermostats 1446
Humidistats 1450 Relative Humidity Sensors 1450 Humidistat Design Features 1452
Bibliography 1453
7.10 VARIABLE-SPEED DRIVES 1454
Introduction 1455 Transportation Efficiency 1455 Characteristics of Variable-Speed Drives 1455
Electromechanical Drives 1456 Mechanical Variable-Speed Drives 1456 Hydraulic Variable-Speed Drives 1458 Magnetic Variable-Speed Drives 1459
Variable Voltage 1461 Pole-Changing AC Motors 1461 Solid-State Variable-Speed Drives 1461
Underlying Semiconductor Technology 1461 Drive Circuit Topologies 1462 Variable-Speed DC Motors 1462
Thyristor DC Drives 1464 Variable-Frequency Drives 1465 Comparison of Solid-State Drives 1468 Efficiency of Solid-State Drives 1469 Recent VFD Developments 1469
Efficiency of Variable-Speed Drives and Pumps 1469
Evaluation of VSD Efficiencies 1470 Conclusions 1471 Bibliography 1471
INTRODUCTION
Dampers and louvers are used to control the flow of gases and vapors. These streams usually flow in large ducts at relatively low static pressures. There are both “commercial” and “process control” quality dampers on the market. Commercialquality units are used for the less-demanding applications,
such as heating, ventilation, and air conditioning (HVAC), while the process control-quality units can handle higher pressures, higher temperatures, and corrosive vapors. The process control-quality units also can provide superior leakage and control characteristics.
