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Control valves

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Control valves

  1. 1. CONTROL VALVES SHIVAJI CHOUDHURY
  2. 2. CONTROL VALVES  Control valves are valves used to control conditions such as flow, pressure, temperature, and liquid level by fully or partially opening or closing in response to signals received from controllers that compare a "setpoint" to a "process variable" whose value is provided by sensors that monitor changes in such conditions.
  3. 3. CONTROL VALVE SIZING  The control valve shall be of globe body design with single port. The valve trim, shall be suitable for quick removal without any cutting or welding.  Sizing shall be accordance with ANSI/ISA 75.01,01.  Valve outlet velocity does not excesed 8 m/sec for liquid service and 150 m/sec for steam services.
  4. 4. CONTROL VALVE SIZING  The valve sizing shall be suitable for obtaining maximum flow conditions with valve opening at approx 80% of total valve stem travel and minimum flow conditions with valve stem travel not less than 10% of total valve stem travel.  All valves shall capable of handling at least 120% of required maximum flow.  Valve body rating shall meet the pressure and temperature requirement as per ANSI B 16.34.
  5. 5. VALVE CONSTRUCTION  Conform to requirement of ANSI for dimensions, material thickness and material specification for their respective pressure class.  All valves shall be globe body design.  All valves connected to vacuum on down stream side shall be provided with packing suitable for vacuum application (e.g double vee type chevon packing).  Extension bonnets shall be provided when the maximum temperature of flowing fluid is greater than 275 deg c.  If the downstream is subjected to vacuum, flow direction of the fluid shall be to close.
  6. 6. TOP GUIDED CONTROL VALVE Top-guided, single-ported valves may be used for tight shutoff applications; however, because these valves are unbalanced, they can require more force from the actuator to achieve shutoff if the flow is under the plug.
  7. 7. CAGE GUIDED VALVES  Cage-guided valves have a cylindrical plug guided through a guide.  The increased guiding area is desirable for high pressure drop, high noise, and anticavitation applications  Unbalanced types can provide a tight shutoff if sufficient  For balanced styles, the plug is vented and the process pressure interacts with the top and bottom side of the plug.
  8. 8. DOUBLE SEATED CONTROL VALVE  Double-seated control valves are used to a lot of industrial applications due to advantages of reduction in actuator force, a great flow capacity and a deal of slurry fluids.  Double-seated valves cannot provide the same shutoff capability as the single-ported types.
  9. 9. Characterized Cages/Trim for Globe valve QUICK OPENING EQUAL PERCENTAGE LINEAR
  10. 10. GLAND PACKING  PTFE if fluid temperature is less than 180 deg C.  Graphite if fluid temperature is more than 180 deg C.  All valves connected to vacuum on down stream side shall be provided with packing suitable for vacuum application (e.g double vee type chevon packing). GLAND PACKING
  11. 11. CAVITATION  Cavitation is a two stage phenomena with liquid flow.  The first stage is the formation of vapor bubbles in the liquid as the fluid passes through the trim and the pressure is reduced below the fluid's vapor pressure.  The second stage is the collapse of the vapor bubbles as the fluid passes the vena contracta and the pressure recovers and increases above the vapor pressure.  The collapsing bubbles are very destructive when they contact metal parts and the bubble collapse may produce high noise levels.
  12. 12. Cavitation  Cavitation in control valves can have four negative effects; • Restricts fluid flow • Causes severe vibrations • Erodes metal surfaces • Generates high noise levels.
  13. 13. ANTI CAVITY TRIM  The anti cavity trim of control valve shall be multi stage ,multi path type.  ISA- RP75.23 – 1995, “Considerations for Evaluating Control Valve Cavitation”, Recommended Practice, June 1995  The High FL Factor ( pressure recovery factor) shall be 0.98 or better.
  14. 14. Cavitation is alleviated by anti-cavitation valve trim
  15. 15. Anti cavitation Trim
  16. 16. Steam conditioning valve steam conditioning valve is primarily used in industrial and utility power plants for the conditioning of auxiliary and process steam,
  17. 17. BODY/TRIM MATERIAL  SEVERE FLASHING/CAVITATION SERVICES BODY MATERIALS- Alloy steel as per ASTM – A217 GR WC 9 TRIM MATERIAL-- 440 C series SS  LOW FLASHING/CAVITATION SERVICES BODY MATERIALS--Alloy steel as per ASTM A – 217 GR WC 6 TRIM MATERIAL- 17-4 PH SS  Non flashing/non cavitation services BODY MATERIALS- carbon steel ASTM A216 Gr WCB Fluid temp below 275 deg C and above 275 deg C – ALLOY STEEL A217 GR WC 9 and 316 SS for DM water service etc TRIM MATERIAL -316SS stellited with stellited faced guide posts and bushings.
  18. 18. Design Practices to Minimize Corrosion  Corrosion in valves can be minimized or eliminated by selecting materials that do not react with the fluid or with the material around them.  Corrosion is the deterioration of a metal by reaction with the environment.  Corrosion is generally controlled by selecting corrosion resistant materials.  Corrosion resistance of a component can be improved by plating, cladding, overlaying, or heat-treating of the wetted surfaces.  The rate of corrosion is influenced by the fluid velocity media and temperature.
  19. 19. Corrosion Ranking for Materials Selection
  20. 20. CONTROL VALVE SEAT LEAKAGE CLASSIFICATION (ANSI/FCI 70-2-1991) S.N LEAKAGE CLASS MAX LEAKAGE ALLOWABLE 1 I --- 2 II 0.5 % of rated capacity 3 III 0.1 % of rated capacity 4 IV 0.01 % OF RATED CAPACITY 5 V 0.0005 ml per minute of water per inch of orifice per psi differential
  21. 21. NOISE  Control valve induced noise shall be limited to 85 db at 1 mtr from valve surface under actual operating condition .  The noise abetment shall be achieved by valve body and trim design or by use of silencers.  Noise calculation shall be as per ISA-75-17-1989.  VALVE with Cage-Style Noise Abatement
  22. 22. END PREPARATION  Valve body ends shall be either butt welded/socket welded, flanged .  The welded ends wherever required shall be butt welded type as per ANSI B 16.25 for control valves of sizes 65 mm and above.  For valves size 50 mm and below welded ends shall be socket welded as per ANSI B 16.11  Flanged ends wherever required shall be of ANSI pressure-temperature class equal to or greater than that of control valve body.
  23. 23. Valve actuators The basic types of actuators are:  · Manual  · Electric motor  · Solenoid  · Pneumatic  · Hydraulic  · Electrohydraulic  · A combination of these types
  24. 24. SMART POSITIONER  smart digital microprocessor based valve positioners and compatibility for remote calibration & superimposed HART signal on input signal 4-20 m Amp & connected with hart management system.
  25. 25. TESTS  i) Non destructive test - ANSI B-16.34  ii) Hydrostatic shell test - ANSI B 16.34  iii) Valve seat leakage- ANSI- B 16.34.  iv) Functional test: The fully assembled valves including actuators control devices and accessories shall be functionally tested .  v) CV test: CV test - ISA 75.02
  26. 26. STANDARDS  ANSI/ISA-75.01.01 (IEC 60534-2-1 Mod) - 2007 - Flow Equations for Sizing Control Valves  ANSI/ISA – SP75.02, 1996, “Control Valve Capacity Test Procedure”, October 1996  ISA- RP75.23 – 1995, “Considerations for Evaluating Control Valve Cavitation”, Recommended Practice, June 1995  ANSI/ISA-75.19.01-2001 (R2007) - Hydrostatic Testing of Control Valves  ISA-75.17-1989 - Control Valve Aerodynamic Noise Prediction  IBR
  27. 27. THANKING YOU

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