SIZING CALCULATIONS FOR GASES AND VAPORSKnown Volume:
A = SCFM X
√ MW X
√ Ta
6.32 X C X PaS X Kd
Known Flow Area:
SCFM = 6.32 X C X PaS X Kd X A
√MW X
√ Ta
Where:
A = Orifice area in square inches
SCFM = Standard Cubic Feet Per Minute
MW = Molecular Weight of Gas or Vapor
Ta = Temperature, degrees F, Absolute (460 + degrees F)
Kd = Coefficient of Discharge 0.859
C = Change of State Coefficient (Where N = 1.25 tp 1.30, USE 345)
PaS = Set Pressure, PSI Absolute (set pressure + 14.7) or
(set Pressure + overpressure + 14.7) as required
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SIZING CALCULATIONS FOR LIQUIDS
Known Volume:
A = GPM X √ SG
38 Kd X √ P1 - P2
Known Flow Area:
GPM = 38Kd X √ (P1 - P2) X A
√ SG
Where:
A = Orifice area in square inches
GPM = Flow rate, gallons per minute
Kd = Coefficient of discharge 0.674
P1 = Pilot Set Pressure
P2 = Back Pressure on discharge side of the valve
SG = Specific Gravity of Liquid at flowing temperature
(Water = 1 @ 70 Degree F)
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