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Control Valves

A short presentation on control valves. Just to get you started.

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Control Valves

  1. 1. Control Valves  A Control Valve is a power-operated device used to modify the fluid flow rate in a process system.  There are two basic types of control valves Control Valve a) Rotary motion valves having ball, butterfly or plug type closures. b) Linear motion valves having globe , diaphragm or pinch type closures.
  2. 2. Control Valve Classification Control Valve Linear Rotary Motion Motion Globe Diaphragm Pinch Ball Butterfly Plug Control Valve Globe Angle 3 way Single Double Seated Seated
  3. 3. Linear Motion  Types Of Closure 1.Globe 1.1. Single Seated 1.2. Double Seated 1.3 Three way 2. Diaphragm 3. Pinch  Linear Valve Features Control Valve i. TORTUOUS FLOW PATH ii. LOW RECOVERY iii. CAN THROTTLE SMALL FLOW RATES iv. OFFERS VARIETY OF SPECIAL TRIM DESIGNS v. SUITED TO HIGH-PRESSURE APPLICATIONS vi. USUALLY FLANGED OR THREADED vii. SEPARABLE BONNET
  4. 4. Single Seated Globe Valve  Features o Large amount of force required to drive the stem o Tight shut off o Used in small diameter applications  Applications Control Valve o Used for controlling large range of process parameters hence used in oil and gas production, power generation
  5. 5. Double Seated Globe Valve  Features o Stem can be driven with small amount of force o Can not achieve perfect closure resulting in leakage o Used in larger diameter applications o Body parts wear out due to Control Valve erosion and cavitations which results in annoying noises  Applications o Used for high flow and high pressure services
  6. 6. Three Way Valves  Features o High flow capacity o Valve used for mixing and diverting liquids. o High rangeability o Leakage capability consistent with normal Control Valve single seated globe valve  Applications o Used in textile industries
  7. 7. Diaphragm Valves • Features o Consists of a saddle or seat upon which the diaphragm closes the valves. o Can handle corrosive fluids.  Applications o Used as shut off Control Valve valves in food and beverage , pharmaceutical and biotech industries
  8. 8. Pinch Valve • Features o Tight shut off o The flexible sleeve allows the valve to close drop tight around solids , solids that would typically be trapped by the seat or Control Valve stuck in crevices in globe, diaphragm, butte rfly, gate or ball valves. • Applications •Best used in controlling corrosive
  9. 9. Rotary Motion  Types Of Closure 1. Ball 2. Butterfly 3. Plug  Rotary Valve Features i. STREAMLINED FLOW PATH ii. HIGH RECOVERY Control Valve iii. MORE CAPACITY iv. LESS PACKING WEAR v. CAN HANDLE SLURRY AND ABRASIVES vi. FLANGELESS vii. INTEGRAL BONNET viii. HIGH RANGEABILITY
  10. 10. Ball Valve  Features o Tight Shut Off o Minimum obstruction for the flowing media. o High flow capacity o Can withstand high pressure and temperatures Control Valve  Applications o Used for hazardous and corrosive fluids
  11. 11. Butterfly Valve  Features o High flow capacity o Unlike ball valve the disc is present in the flow of the liquid and hence a pressure drop is always induced in the flow. Control Valve o Tight shut off  Applications o Used in Steel , Sugar and textile industries
  12. 12. Actuators In control valve we have seen that , the operation of a control valve involves positioning its movable part (the plug, ball or vane) relative to the stationary seat of the valve. The purpose of the valve actuator is to accurately locate the valve plug in a position dictated by the control signal. The actuator accepts a signal from the control system and, in response, moves the valve to a fully-open or fully-closed position, or a more open or a more closed position The major types of actuators are : 1. Pneumatic type 2. Electric type
  13. 13. Pneumatic Actuators They are basically of two types 1. Piston actuator 2. Diaphragm actuator These actuators are designed so that with a specific change of air pressure, the spindle will move sufficiently to move the valve through its complete stroke from fully-closed to fully-open.
  14. 14. Piston Actuator  They can withstand higher input pressures.  Can offer small cylinder volumes.  They are generally used where the stroke of a diaphragm actuator would be too short or the thrust is too small.
  15. 15. Diaphragm Actuators • They have compressed air applied to a flexible membrane called the diaphragm • They are single acting i.e. air is supplied from single side of the diaphragm
  16. 16. Diaphragm Actuators
  17. 17. Electric Actuators  Electric actuators use an electric motor with voltage requirements in the following range: 230 Vac, 110 Vac, 24 Vac and 24 Vdc.  There are two types of electrical actuator 1. VMD (Valve Motor Drive) 2. Modulating.
  18. 18. VMD ( Valve Motor Drive )  This basic version of the electric actuator has three states: I. Driving the valve open. II. Driving the valve closed. III. No movement • The controller positions the valve by driving the valve open or closed for a certain time, to ensure that it reaches the desired position. Valve position feedback may be used with some controllers.
  19. 19. Modulating  In order to position the control valve in response to the system requirements a modulating actuator can be used. These units may have higher rated motors (typically 1 200 starts/hour) and may have built-in electronics.  A positioning circuit may be included in the modulating actuator which accepts an analogue control signal (typically 0- 10 V or 4-20 mA). The actuator then interprets this control signal, as the valve position between the limit switches.  To achieve this, the actuator has a position sensor (usually a potentiometer), which feeds the actual valve position back to the positioning circuit. In this way the actuator can be positioned along its stroke in proportion to the control signal.
  20. 20. Control Valve Thank You