CONTROL VALVE HANDBOOK Episode 1 Part 5 ppt

67 Chapter 4 Control Valve Accessories This chapter offers information on digital valve controllers, analog positioners, boosters, and other control valve accessories. Positioners Pneumatically operated valves de- pend on a positioner to take an input signal from a process controller and convert it to valve travel. These instruments are available in three configura- tions: 1. Pneumatic Positioners—A pneumatic signal (usually 3-15 psig) is supplied to the positioner. The positioner translates this to a required valve position and supplies the valve actuator with the required air pressure to move the valve to the correct position. 2. Analog I/P Positioner—This positioner performs the same function as the one above, but uses electrical current (usually 4-20 mA) instead of air as the input signal. 3. Digital Controller—Although this instrument functions very much as the Analog I/P described above, it differs in that the electronic signal conversion is digital rather than analog. The digital products cover three categories. D Digital Non-Communicating—A current signal (4-20 mA) is supplied to the positioner, which both powers the electronics and controls the output. D HART—This is the same as the digital non-communicating but is also capable of two-way digital commu- nication over the same wires used for the analog signal. D Fieldbus—This type receives digitally based signals and positions the valve using digital electronic cir- cuitry coupled to mechanical compo- nents. An all-digital control signal re- Chapter 4. Control Valve Accessories 68 Figure 4-1. Modern Control Valves Utilizing Digital Valve Controllers W8861 W8119-1 places the analog control signal. Additionally, two-way digital commu- nication is possible over the same wires. Fieldbus technologies benefit the end user by enabling improved control architecture, product capability and reduced wiring. Use of a single, integrated analog I/P positioner or digital controller (figure 4-1) instead of a combination of pneumatic positioner and transducer (two instruments) results in lower installed cost. The ability to embed software com- mands into the memory of the device represents the real difference between digital and analog I/P seg- ments. This allows automatic configu- ration and setup of the valve when equipped with a digital controller. Most importantly, it allows two-way commu- nication for process, valve, and instrument diagnostics. Users purchase digital valve controllers for several reasons: D Reduced cost of loop commis- sioning, including installation and calibration. D Use of diagnostics to maintain loop performance levels. D Improved process control accu- racy that reduces process variability. Two aspects of digital valve controllers make them particularly attractive: D Automatic calibration and config- uration. Considerable time savings are realized over traditional zero and spanning. D Valve diagnostics. Through the Distributed Control System (DCS), PC software tools, or handheld communi- cators, users can diagnose the health of the valve while it is in the line. FIELDVUER instruments enable new diagnostic capabilities that can be ac- cessed remotely. This single element requires a look at the potential impact of the technology as it applies to control valves. An in-plant person, with the aid of the FlowScannert system, can diagnose the health of a valve through a series of off-line tests. The FlowScanner system consists of a portable, ruggedized computer and travel and pressure sensors. The sensors are connected to the valve to enable diagnostic tests, which are conducted with the valve off-line. A skilled maintenance techni- cian can determine whether to leave the valve in the line or to remove the valve for repair. Digital instruments allow an extension of this service with added enhance- ments: D Because sensors are part of the instrument, tests can be run easily at appropriate times. Chapter 4. Control Valve Accessories 69 Figure 4-2. Positioner Schematic for Diaphragm Actuator OUTPUT TO DIAPHRAGM RELAY INSTRUMENT BELLOWS FEEDBACK AXIS PIVOT NOZZLE FLAPPER DIRECT ACTION QUADRANT INPUT AXIS CAM REVERSE ACTION QUADRANT BEAM ACTUATOR VALVE STEM CONNECTION SUPPLY 22A7965-A A2453-2 / IL D It is now possible to diagnose the health of a valve remotely via HART or Foundation fieldbus. D On-line diagnostics enable predictive maintenance without disrupting the process. These additional elements are ex- tremely important. The remote capability allows monitoring valves. Those who make, supply and service valves for a living now assist the customer in the diagnosis of valve condition to a level never before possible. Predictive maintenance offers additional savings for the customer. It is now possible to see the performance of the valve as it operates. Watching performance de- cline over time enables the user to predict when replacement or repair is necessary. Other Control Valve Accessories Figure 4-5 illustrates a top-mounted handwheel for a direct-acting diaphragm actuator. This unit can be used as an adjustable travel stop to limit travel in the upward direction or to manually close push-down-to-close valves. Figure 4-6 illustrates a top-mounted handwheel for a reverse-acting diaphragm actuator. This unit can be used as an adjustable travel stop to limit travel in the downward direction or to manually close push-down-to- open valves. Limit Switches Limit switches operate discrete inputs to a distributed control system, signal lights, small solenoid valves, electric relays, or alarms. The cam-operated type (figure 4-7) is typically used with Chapter 4. Control Valve Accessories 70 Figure 4-3. Positioner Schematic for Piston Actuator A1304/IL INPUT SIGNAL BYPASS RESTRICTION ADJUSTING SCREW BYPASS RESTRICTION SUPPLY PORT OUTPUT TO ACTUATOR SUPPLY EXHAUST EXHAUST PORT DIAPHRAGMS W0679-1/IL Figure 4-4. Volume Booster Chapter 4. Control Valve Accessories 71 Figure 4-5. Top-Mounted Hand- wheel for Direct-Acting Diaphragm Actuator W0368-1/IL Figure 4-6. Top-Mounted Hand- wheel for Reverse-Acting Dia- phragm Actuator W0369-1/IL two to four individual switches operated by movement of the valve stem. An assembly that mounts on the side of the actuator houses the switches. Each switch adjusts individually and can be supplied for either alternating current or direct current systems. Oth- er styles of valve-mounted limit switches are also available. Figure 4-7. Cam-Operated Limit Switches A7095/IL W2078/IL Solenoid Valve Manifold The actuator type and the desired fail- safe operation determine the selection of the proper solenoid valve (figure 4-8). The solenoids can be used on double-acting pistons or single-acting diaphragm actuators. Supply Pressure Regulator Supply pressure regulators (figure 4-9), commonly called airsets, reduce plant air supply to valve positioners and other control equipment. Com- mon reduced-air-supply pressures are 20, 35 and 60 psig. The regulator mounts integrally to the positioner, or nipple-mounts or bolts to the actuator. Chapter 4. Control Valve Accessories 72 Figure 4-8. Solenoid Valve W7007/IL Figure 4-9. Supply Pressure Regulator with Filter and Moisture Trap W0047/IL Pneumatic Lock-Up Systems Pneumatic lock-up systems (figure 4-10) are used with control valves to lock in existing actuator loading pressure in the event of supply pressure failure. These devices can be used with volume tanks to move the valve to the fully open or closed position on loss of pneumatic air supply. Normal operation resumes automatically with restored supply pressure. Functionally similar arrangements are available for control valves using diaphragm actuators. Fail-Safe Systems for Piston Actuators In these fail-safe systems (figure 4-11), the actuator piston moves to the top or bottom of the cylinder when supply pressure falls below a pre-de- termined value. The volume tank, charged with supply pressure, pro- vides loading pressure for the actuator piston when supply pressure fails, thus moving the piston to the desired position. Automatic operation resumes, and the volume tank is re- charged when supply pressure is restored to normal. Electro-Pneumatic Transducers Figure 4-12 illustrates an electro- pneumatic transducer. The transducer receives a direct current input signal and uses a torque motor, nozzle-flapper, and pneumatic relay to convert the electric signal to a proportional pneumatic output signal. Nozzle pressure operates the relay and is piped to the torque motor feedback bellows to provide a comparison between input signal and nozzle pressure. As shown, the transducer can be mounted directly on a control valve and operate the valve without need for additional boosters or positioners. Chapter 4. Control Valve Accessories 73 Figure 4-10. Lock-Up System Schematic for Piston Actuator 35A6998-C A2285-4/IL Figure 4-11. Typical Schematic of a “Fail-Safe” System 35A6996-C A2283-4/IL Chapter 4. Control Valve Accessories 74 Figure 4-12. Electro-Pneumatic Transducer Mounted on a Dia- phragm-Actuated Control Valve ELECTRO- PNEUMATIC TRANSDUCER W8723−1 Electro-Pneumatic Valve Positioners Electro-pneumatic positioners (figure 4-13) are used in electronic control loops to operate pneumatic diaphragm control valve actuators. The positioner receives a 4 to 20 mA DC input signal, and uses an I/P convert- er, nozzle-flapper, and pneumatic relay to convert the input signal to a pneumatic output signal. The output signal is applied directly to the actuator diaphragm, producing valve plug position that is proportional to the input signal. Valve plug position is me- chanically fed back to the torque comparison of plug position and input signal. Split-range operation capability can provide full travel of the actuator with only a portion of the input signal range. Diagnostics Digital valve controllers incorporate predefined instrument and valve diag- Figure 4-13. Electro-Pneumatic Positioner on Diaphragm Actuator W4930/IL nostics within firmware to provide alerts if there are problems with instrument mounting, electronics, hardware or valve performance. HART-based handheld field communi- cators when connected to the digital valve controllers enable user-config- ured alerts and alarms. These flags provide notification of current status and potential valve and instrument problems. Typical alerts include travel deviation, travel limit, cycle count and travel accumulation. AMS ValveLinkR software allows tests that identify problems with the entire control valve assembly. Using the valve stem travel feedback, actuator pressure sensor and other sensors on the instrument, the health of the control valve can be evaluated while the valve is still in service and fully op- erational. This helps to pinpoint problems before the equipment fails, without disrupting the process. 75 Chapter 5 Control Valve Selection Control valves handle all kinds of fluids at temperatures from the cryo- genic range to well over 1000_F (538_C). Selection of a control valve body assembly requires particular consideration to provide the best available combination of valve body style, material, and trim construction design for the intended service. Ca- pacity requirements and system oper- ating pressure ranges also must be considered in selecting a control valve to ensure satisfactory operation without undue initial expense. Reputable control valve manufactur- ers and their representatives are dedi- cated to helping select the control valve most appropriate for the existing service conditions. Because there are frequently several possible correct choices for an application, it is important that all the following information be provided: D Type of fluid to be controlled D Temperature of fluid D Viscosity of fluid D Specific gravity of fluid D Flow capacity required (maximum and minimum) D Inlet pressure at valve (maximum and minimum) D Outlet pressure (maximum and minimum) D Pressure drop during normal flowing conditions D Pressure drop at shutoff D Maximum permissible noise level, if pertinent, and the measurement reference point D Degrees of superheat or exis- tence of flashing, if known Chapter 5. Control Valve Selection 76 D Inlet and outlet pipeline size and schedule D Special tagging information required D Body Material (ASTM A216 grade WCC, ASTM A217 grade WC9, ASTM A351 CF8M, etc.) D End connections and valve rat- ing (screwed, Class 600 RF flanged, Class 1500 RTJ flanges, etc.) D Action desired on air failure (valve to open, close, or retain last controlled position) D Instrument air supply available D Instrument signal (3 to 15 psig, 4 to 20 mA, Hart, etc.) In addition the following information will require the agreement of the user and the manufacturer depending on the purchasing and engineering prac- tices being followed. D Valve type number D Valve size D Valve body construction (angle, double-port, butterfly, etc.) D Valve plug guiding (cage-style, port-guided, etc.) D Valve plug action (push-down-to-close or push-down-to- open) D Port size (full or restricted) D Valve trim materials required D Flow action (flow tends to open valve or flow tends to close valve) D Actuator size required D Bonnet style (plain, extension, bellows seal, etc.) D Packing material (PTFE V-ring, laminated graphite, environmental sealing systems, etc.) D Accessories required (positioner, handwheel, etc.) Some of these options have been dis- cussed in previous chapters of this book, and others will be explored in this and following chapters. VALVE SELECTION PROCESS DETERMINE SERVICE CONDITIONS S (P 1 , ∆P, Q, T 1 , Fluid Properties, Allow- able Noise, etc). S Select appropriate ANSI Pressure Class required for valve body and trim. CALCULATE PRELIMINARY C v REQUIRED S Check noise and cavitation levels SELECT TRIM TYPE S If no noise or cavitation indication, choose standard trim. S If aerodynamic noise is high, choose Whis- per Trim R . S If liquid noise is high and/or cavitation is in- dicated, choose Cavitrol R III trim. SELECT VALVE BODY AND TRIM SIZE S Select valve body and trim size with required C v . S Note travel, trim group, and shutoff options. SELECT TRIM MATERIALS Select trim materials for your application; make sure trim selected is available in the trim group for the valve size selected. OPTIONS Consider options on shutoff, stem packing, etc. Valve Body Materials Body material selection is usually based on the pressure, temperature, [...]... 780 1, 1 65 1, 9 45 950 35 380 7 65 1, 1 45 1, 910 10 00 20 320 640 9 65 1, 6 05 10 50 20 (1) 310 6 15 9 25 1, 54 5 11 00 20 (1) 255 51 5 770 1, 2 85 11 50 20 (1) 200 400 59 5 9 95 12 00 20 (1) 15 5 310 4 65 770 12 50 20 (1) 11 5 2 25 340 56 5 13 00 20 (1) 85 17 0 255 430 13 50 20 (1) 60 12 5 18 5 310 14 00 20 (1) 50 95 14 5 240 14 50 15 (1) 35 70 10 5 17 0 15 00 10 (1) 25 55 80 13 5 _C Bar −29 to 38 19 50 99 14 9 248 93 16 41 83 12 4 207 14 9 14 37 74 11 2... 7 45 1, 490 2,2 35 3,7 25 300 230 7 15 1, 430 2 , 15 0 3 ,58 0 400 200 7 05 1, 410 2 ,11 5 3 ,53 0 50 0 17 0 6 65 1, 330 1, 9 95 3,3 25 600 14 0 6 05 1, 210 1, 8 15 3,0 25 650 12 5 590 1, 1 75 1, 7 65 2,940 700 11 0 57 0 1, 1 35 1, 7 05 2,840 750 95 530 1, 055 1, 58 5 2,640 800 80 51 0 1, 0 15 1, 52 5 2 ,54 0 850 65 4 85 9 65 1, 450 2, 4 15 900 50 370 740 1, 110 1, 850 950 35 2 75 550 8 25 1, 370 10 00 20 200 400 59 5 9 95 10 50 20 (1) 14 5 290 430 720 11 00 20 (1) 10 0... 51 0 1, 0 15 1, 52 5 2 ,54 0 850 65 4 85 9 75 1, 460 2,4 35 900 50 450 900 1, 350 2,2 45 950 35 3 75 755 1, 130 1, 8 85 10 00 20 260 52 0 780 1, 3 05 10 50 20 (1) 17 5 350 52 5 8 75 11 00 20 (1) 11 0 220 330 55 0 _C Bar −29 to 38 20 52 10 3 15 5 259 93 18 52 10 3 15 5 259 14 9 16 50 10 0 15 1 2 51 204 14 49 97 14 6 243 260 12 46 92 13 8 229 316 10 42 83 12 5 209 343 9 41 81 122 203 3 71 8 39 78 11 8 19 6 399 7 37 73 11 0 18 3 427 6 35 70 10 5 17 5. .. 1, 720 11 00 20(2) 3 05 610 9 15 1, 52 5 11 50 20(2) 2 35 4 75 710 1, 1 85 12 00 20(2) 18 5 370 55 5 9 25 12 50 20(2) 14 5 2 95 440 7 35 13 00 20(2) 11 5 2 35 350 58 5 13 50 20(2) 95 19 0 290 480 14 00 20(2) 75 15 0 2 25 380 14 50 20(2) 60 11 5 17 5 290 15 00 20(2) 40 85 12 5 2 05 _C Bar −29 to 38 19 50 99 14 9 248 93 16 43 85 12 8 213 14 9 15 39 77 11 6 19 3 204 13 36 71 106 17 7 260 12 33 66 99 16 5 316 10 31 62 93 15 5 343 9 31 61 92 15 3 3 71. .. 15 00 Psig 200 2 35 620 1, 240 1, 860 3,0 95 300 2 15 56 0 1, 120 1, 680 2,7 95 400 19 5 51 5 1, 0 25 1, 54 0 2 ,57 0 50 0 17 0 480 955 1, 4 35 2,390 600 14 0 450 900 1, 355 2, 255 650 12 5 4 45 890 1, 330 2,220 700 11 0 430 870 1, 3 05 2 ,17 0 750 95 4 25 855 1, 280 2 ,13 5 800 80 420 8 45 1, 2 65 2 ,11 0 850 65 420 8 35 1, 255 2,090 900 50 4 15 830 1, 2 45 2,0 75 950 35 3 85 7 75 1, 160 1, 930 10 00 20 350 700 1, 050 1, 750 10 50 20(2) 3 45 6 85 1, 030 1, 720... 12 .12 311 12 . 25 314 12 .37 80 3 298 11 . 75 311 12 . 25 318 12 .50 333 13 .12 337 13 . 25 340 13 .37 10 0 4 352 13 .88 3 65 14 .38 368 14 .50 384 15 .12 394 15 .50 397 15 .62 15 0 6 4 51 17. 75 464 18 . 25 473 18 .62 489 19 .24 50 8 20.00 51 1 20 .12 200 8 54 3 21. 38 55 6 21. 88 56 8 22.38 58 4 23.00 610 24.00 613 24 .12 250 10 673 26 .50 686 27.00 708 27.88 724 28 .50 752 29.62 755 29.74 300 12 737 29.00 749 29 .50 7 75 30 .50 790 31. 12 819 ... 1, 1 75 1, 7 65 2,940 700 11 0 57 0 1, 1 35 1, 7 05 2,840 750 95 5 05 1, 010 1, 51 0 2 ,52 0 800 80 410 8 25 1, 2 35 2,060 _C Bar −29 to 38 52 10 3 15 5 259 18 52 10 3 15 5 259 14 9 16 50 10 0 15 1 2 51 204 14 49 97 14 6 243 260 12 46 92 13 8 229 316 10 42 83 12 5 209 343 9 41 81 122 203 3 71 8 39 78 11 8 19 6 399 7 35 70 10 4 17 4 427 78 20 93 6 28 57 85 14 2 Chapter 5 Control Valve Selection Cast Chromium-Molybdenum Steel (ASTM A 217 ... A 216 Cast Iron Valves (in accordance with ASME/ANSI B16 .1) CLASS 12 5 TEMPERATURE CLASS 250 ASTM A 216 ASTM A 216 Class A Class B Class A NPS 1- 12 NPS 1- 12 NPS 14 -24 −20 to 15 0 17 5 200 200 16 5 2 25 Class B NPS 1- 12 NPS 1- 12 NPS 14 -24 15 0 400 50 0 300 19 0 13 5 370 460 280 15 5 18 0 13 0 355 440 270 250 15 0 17 5 12 5 340 4 15 260 2 75 14 5 17 0 12 0 3 25 3 95 250 300 14 0 16 5 11 0 310 3 75 240 3 25 13 0 15 5 10 5 2 95 355 230... ASTM A 217 Grade WC9 Valves (in accordance with ASME B16.34) WORKING PRESSURES BY CLASS, PSIG TEMPERATURE, _F 15 0 300 600 900 15 00 −20 to 10 0 290 750 1, 50 0 2, 250 3, 750 200 260 750 1, 50 0 2, 250 3, 750 300 230 730 1, 455 2 ,18 5 3,640 400 200 7 05 1, 410 2 ,11 5 3 ,53 0 50 0 17 0 6 65 1, 330 1, 9 95 3,3 25 600 14 0 6 05 1, 210 1, 8 15 3,0 25 650 12 5 590 1, 1 75 1, 7 65 2,940 700 11 0 57 0 1, 1 35 1, 7 05 2,840 750 95 530 1, 0 65 1, 59 5 2,660... 250 RF (CI) CL 300 RF (STL) mm in mm in mm in 15 1/ 2 18 4 7. 25 19 7 7. 75 19 0 7 .50 202 7.94 203 8.00 203 8.00 20 3/4 18 4 7. 25 19 7 7. 75 19 4 7.62 206 8 .12 206 8 .12 206 8 .12 25 1 184 7. 25 19 7 7. 75 19 7 7. 75 210 8. 25 210 8. 25 210 8. 25 40 1 1/ 2 222 8. 75 2 35 9. 25 2 35 9. 25 248 9. 75 2 51 9.88 2 51 9.88 50 2 254 10 .00 267 10 .50 267 10 .50 282 11 .12 286 11 . 25 284 11 .37 65 2 1/ 2 276 10 .88 289 11 .38 292 11 .50 308 12 .12 . 2 ,11 5 3 ,53 0 50 0 17 0 6 65 1, 330 1, 9 95 3,3 25 600 14 0 6 05 1, 210 1, 8 15 3,0 25 650 12 5 590 1, 1 75 1, 7 65 2,940 700 11 0 57 0 1, 1 35 1, 7 05 2,840 750 95 530 1, 0 65 1, 59 5 2,660 800 80 51 0 1, 0 15 1, 52 5 2 ,54 0 850 . 7 15 1, 430 2 , 15 0 3 ,58 0 400 200 7 05 1, 410 2 ,11 5 3 ,53 0 50 0 17 0 6 65 1, 330 1, 9 95 3,3 25 600 14 0 6 05 1, 210 1, 8 15 3,0 25 650 12 5 590 1, 1 75 1, 7 65 2,940 700 11 0 57 0 1, 1 35 1, 7 05 2,840 750 95 530 1, 055 1, 58 5. 4 05 8 05 1, 210 2, 0 15 850 65 3 95 790 1, 190 1, 980 900 50 390 780 1, 1 65 1, 9 45 950 35 380 7 65 1, 1 45 1, 910 10 00 20 320 640 9 65 1, 6 05 10 50 20 (1) 310 6 15 9 25 1, 54 5 11 00 20 (1) 255 51 5 770 1, 2 85 11 50