Axelson Orifice

A common question we are asked pertains to orifice selections on Axelson Valves.
Following, please find an Orifice Selection Chart:

AVAILABLE ORIFICE SIZES FOR TYPE HF, HD, AND HL PILOT OPERATED RELIEF VALVES

VALVE COEFFICIENT, 0.859

orifice-charts

Known 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

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)