Formula source of flow capacity of pressure relief deives for gas cylinders in CGA S 1.1 -2019

[yanxingqing]

Hi everyone, I am doing some pressure relief device calculations to gas cylinders according to CGA S 1.1-2019. There are two equations for flow capacity of PRD, Qa=0.154Wc for other PRD except PRV, and Qa=0.00154PWc for PRV. Qa is the flow capacity in ft3/min of free air, Wc is water capacity of the cylinder in pounds, and P is flow rating pressure in psia. I am confused about the deviation of these two equation. Why Qa is irrelevant to P for other PRD except PRV but is relevant to P for PRV? Could anyone tell me the devation of the euqations? or tell me where I can find the information on this. The information like documents, standards that require payment can also be accepted.
Thanks in advance for the help.

 

[The Obturator]

I think your question would be answered in a different forum such as 'gas compression engineering'. Although your question relates to pressure relief devices, this safety relief valve forum is more for the oil and gas industry type valves following ASME and API codes and standards.

 

[yanxingqing]

I think your question would be answered in a different forum such as 'gas compression engineering'. Although your question relates to pressure relief devices, this safety relief valve forum is more for the oil and gas industry type valves following ASME and API codes and standards.

Thanks, and maybe you are right. I will try to find the answer in different forums.