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Vapor Control Valve Calculation


VAPOR CONTROL VALVE HELP

Vapor control valve calculations are used with the permission of ISA, the Instrumentation, Systems and Automation Society. The calculations are from ANSI/ISA-75.01-1985 (R1995), Flow Equations for Sizing Control Valves. © Copyright 1995, ISA - The Instrumentation, Systems, and Automation Society. For information, contact ISA Standards, www.isa.org.


I used the vapor control valve sizing calculations in section 6 (pages 14 and 15).


These calculations will allow preliminary sizing but in general the control valve vendor should take responsibility for sizing. Further Cv and Xt values should be taken from the vendor's catalogue. The representative values below can be used for preliminary sizing only.



REPRESENTATIVE VALUES OF VALVE CAPACITY FACTORS (Selected from Table D-1 of ANSI/ISA-75.01-1985)
Valve Type Trim Type Flow Direction Xt Fl Fd Cv/dČ
GLOBE Single Port Ported Plug Either 0.75 0.9 1.0 9.5
" Contoured Plug Open 0.72 0.9 1.0 11
" " Close 0.55 0.8 1.0 11
" Characterized Cage Open 0.75 0.9 1.0 14
" " Close 0.70 0.85 1.0 16
" Wing Guided Either 0.75 0.9 1.0 11
GLOBE Double Port Ported Plug Either 0.75 0.9 0.7 12.5
" Contoured Plug Either 0.70 0.85 0.7 13
" Wing Guided Either 0.75 0.9 0.7 14
GLOBE Rotary Eccentric Spherical Plug Open 0.61 0.85 1.0 12
" " Close 0.40 0.68 1.0 13.5
ANGLE Contoured Plug Open 0.72 0.9 1.0 17
" " Close 0.65 0.8 1.0 20
" Characterized Plug Open 0.65 0.85 1.0 12
" " Close 0.60 0.8 1.0 12
" Venturi Close 0.20 0.5 1.0 22
BALL Segmental Open 0.25 0.6 1.0 25
" Standard 80% Port Either 0.15 0.55 1.0 30
BUTTERFLY 60° Aligned Either 0.38 0.68 0.7 17.5
" Fluted Vane Either 0.41 0.7 0.7 25
" 90° Offset Seat Either 0.35 0.60 0.7 29

Notes:

  • Flow direction tends to open or close the valve, i.e. push the closure member away from or towards the seat.
  • In general an Fd value of 1.0 can be used for valves with a single flow passage. An Fd value of 0.7 can be used for valves with two flow passages, such as double-ported valves and butterfly valves.
  • In this table d may be taken as the nominal valve size, in inches.

    References:

  • "ANSI/ISA-75.01-1985 (R1995), Flow Equations for Sizing Control Valves," ISA - The Instrumentation, Systems, and Automation Society (1995).

    Vapor Control Valve Calculation
    Copyrighted 2001, 2003
    Last updated 04May03