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Valve Selection & Sizing
Valve Selection & Sizing
Valve Selection & Sizing
Valve Selection & Sizing
Valve Selection & Sizing
Valve Selection & Sizing
Valve Selection & Sizing
Valve Selection & Sizing
Valve Selection & Sizing
Valve Selection & Sizing
Valve Selection & Sizing
Valve Selection & Sizing
Valve Selection & Sizing
Valve Selection & Sizing
Valve Selection & Sizing
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Valve Selection & Sizing

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Brief description about sizing consideration of valves in process industries & selection as per control strategy.

Brief description about sizing consideration of valves in process industries & selection as per control strategy.

Published in: Education, Business, Technology
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Transcript

  • 1. Valve Sizing & Selection Ranjeet Kumar M.Tech – Chemical
  • 2. Steps in Sizing
    • Science with many rules of thumb
    • Define the System.
    • Maximum Pressure Drop for the Valve.
    • Calculate the valve Characteristics (C v ).
    • Preliminary valve selection.
    • Check the C v and stroke percentage at minimum flow.
    • Check the gain across applicable flow rates.
  • 3. Define the System – Key Variables
    • Total pressure drop,
    • Design flow,
    • Operating flow,
    • Minimum flow,
    • Pipe diameter,
    • Specific gravity
  • 4. Maximum Allowable Pressure Drop
    • The usual rule of thumb is that a valve should be designed to use 10-15% of the total pressure drop or 10 psi, whichever is greater .
    • Investigate the Pump & its maximum available head.
    • MAPD = NPHSA – NPSHR.
    • Trade off-
      • larger pressure drops increase the pumping cost (operating) &
      • smaller pressure drops increase the valve cost because a larger valve is required (capital cost).
  • 5. Valve Characteristics – C v
    • Note – Check thumb rules before referring valve chart or characteristic curve.
  • 6. Preliminary Valve Selection
    • Thumb Rules –
      • Never use a valve that is less than half the pipe size.
      • Avoid using the lower 10% and upper 20% of the valve stroke. The valve is much easier to control in the 10-80% stroke range.
    • Select the type of valve & use its corresponding valve chart.
    • Valve chart is supplied by manufacturer.
    • Check C v for minimum flow with selected size of valve & check for minimum flow should not fall below 10% of valve stroke.
  • 7. Valve Chart / Characteristics Curve Table 1 – Chart for Equal Percentage Globe Valve
  • 8. Gain across applicable flow rates
    • Gain #1 = 85/38 = 2.2 Gain #2 = 40/12 = 3.3
    • Acceptance criteria :–
      • Gain should never be less than 0.5.
      • Gain#2 – Gain#1 < 50% of (max of Gain#1 or Gain#2)
        • Here 0.5 (3.3) = 1.65 and 3.3 - 2.2 = 1.10.  Since 1.10 is less than 1.65 so it can be a choice
    85 – 73 = 12 150-110 = 40 85 150 73 110 73 – 35 = 38 110 – 25 = 85 35 25 Change in stroke (%) Change in Flow(GPM) Stroke (%) Flow (GPM)
  • 9. Choke Flow F L
    • At max restriction – flow rate is max & pressure is minimum.
    • Vapor bubbles flashes if liquid pressure falls below Vapor Pressure of liquid.
    • Bubbles has (a) no effect on flow, (b) increases pressure drop across valve, (c) cavitations
            • Decreased efficiency
            • Noise
            • Vibration
            • Material loss – sand blasted surface
    • F L checking is recommended when difference in Max & Min flow exceed 90% of Max flow.
  • 10. Basic Valve Types – mechanical characteristics
    • Ball valves;
    • Diaphragm valves;
    • Gate valves;
    • Globe valves;
    • Butterfly valves;
    • Plug valves;
    • Check valve;
    • Safety/relief valve
  • 11. Basic Valve Types – control / openness
    • Equal Percentage :  equal increments of valve travel produce an equal percentage in flow change.
      • Large changes in pressure drop are expected
      • Minimum pressure drop due to valve
      • In temperature & pressure control loop
    • Linear :  valve travel is directly proportional to the valve stoke
      • In liquid level or flow loops
      • Pressure drop across valve is almost constant.
    • Quick opening :  large increase in flow with a small change in valve stroke
      • For frequent on-off services
      • Instantly large flow is needed.
  • 12. Gate Valve
    • Best Suited Control:  Quick Opening
    • Recommended Uses:
      • Fully open/closed, non-throttling
      • Infrequent operation
      • Minimal fluid trapping in line
    • Advantages:   
      • High capacity
      • Tight shut off, Low cost, Little resistance to flow  
      •                      
    • Disadvantages:
      • Poor control
      • Cavitate at low pressure drops
      • Cannot be used for throttling
    • Applications:   Oil, Gas, Air, Slurries, Heavy liquids, Steam, Non-condensing gases, and Corrosive liquids
  • 13. Globe valve
    • Best Suited Control:   Linear and Equal percentage
    • Recommended use-
      • Throtteling services/flow regulation
      • Frequent operation
    • Advantages:
      • Efficient throttling
      • Accurate flow control valves
      • Available in multiple ports  
      •                       
    • Disadvantages:
      • High pressure drop
      • More expensive than other  
    • Applications :   Liquids, vapors, gases, corrosive substances, slurries
  • 14. Ball valve
    • Best suited control – Quick opening linear .
    • Recommended uses –
      • Fully open/closed limited throttling
      • Higher temperature fluids
    • Advantages –
      • Low cost
      • High capacity
      • Low leakage & maintenance
      • Tight sealing with low torque
    • Disadvantages –
      • Poor throttling characteristics
      • Prone to cavitation
    • Applications – Most Liquids, high temperatures, slurries
  • 15. Butterfly valve
    • Best Suited Control:   Linear, Equal percentage
    • Recommended Uses :
      • Fully open/closed or throttling services
      • Frequent operation
      • Minimal fluid trapping in line
    • Advantages :
      • Low cost and maint.
      • High capacity
      • Good flow control
      • Low pressure drop
    • Disadvantages –
      • High torque required to control
      • Prone to cavitation at lower flows
    • Applications :  Liquids, gases, slurries, liquids with suspended solids

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