The following formulas are frequently required in calculating and converting pressure relief valve flow capacities.
To calculate the valve capacity at any set pressure for any gas:
W = CKAP (sqrt) (M/T)
WHERE:
W = flow of gas, lb/hr
C = constant for gas (function of specific heats)
K = coefficient of discharge
A = actual discharge area, sq. in.
P = (set pressure x 1.10) plus 14.7 psia
M = molecular weight
T = absolute temp. at inlet (deg. F +460)
To Convert from lb/hr to SCFM:
SCFM = W x (6.32/M)
Where:
W = flow of gas, lb/hr
M = molecular weight
To calculate the valve capacity for air at 60 degrees F:
SCFM = 18.33 KAP
Where:
K = coefficient of discharge
A = actual discharge area
P = (set pressure x 1.10) plus 14.7 psia
