Relieving capacity of PRV

[v8landy]

Hi

In the following equation
A=(13160W?TZ) / CKP1Kb?M

A = Minium effective discharge area,square millimters
C= Coefficent determined from an expression of the specific heats of gas or vapour at standard condtions (if not known use 315)
K= Effective coefficent of discharge K= 0.975
Kb= Capacity correction factor due to back pressure = 1 for atmospheric
M= Molecular weight of the gas or vapour from standard tables
P1= Reliveing pressure, KiloPascals absolute. This is the set pressure (kPa) + overpressure (kPa) + atmospheric pressure (kPaa)
T= Absolute temperature at the valve inlet, degrees Kelvin (C + 273)
W= Relieving capacity, Kilograms per hour
Z= Compressablity factor. Use Z = 1.0 if value unknown
What would W relate to ? a % of tank volume?

Thanks

 

[lizking]

W is the required relieving flowrate (at relief conditions) established from an overpressure scenario analysis.

 

[v8landy]

Thanks I have just found that myself.

Is A - Minimum effective discharge area,square millimeters

The area of the flange on tank or exit erea of PRV?

 

[lizking]

A is in mm's. It is the relief valve orifice area. Check out API 526 for relief valve body sizes vis-a-vis orifice size.

 

[MortenA]

About A

The way i understood it A is actually more like a nominal area that makes it possible to compare valves from different makers. Ther actual free area may differ but the manufactor will then know how to compensate.

Best regards

Morten