How much critical is molecular weight for pressure control valve

[cherry123]

I want to know how a PCV (Pressure control valve) works.
Only pressure matters regardless of flow? or the flow as well as gas density also matters?

 

[ash9144]

It regulates the downstream pressure. That is all it is interested in. So assuming it is say a nitrogen line supplying your regulator as the downstream pressure goes down the valve opens to increase the downstream pressure. Could also have on a vacuum system but reverse as pressure goes up valve to suction of vac pump opens.

 

[JimCasey]

The capacity (Cv) calculation for the PCV asks for the density of the gas. The molecular weight determines the density of an ideal gas. You'll also need the ratio of specific heats (k) and the critical pressure Pc for most equations.

 

[dcasto]

Basically it comes down to this, how many pounds/hour or mass rate do you want to flow and what pressure drop do you want. The density or gravity adjusts from standard to flowing conditions and the K (Cp/Cv) adjusts for, molecule size and distance between molecules the speed of sound which places an upper limit on the system.

Generally, if the pressure drop required increases, the port area needed to pass a fixed mass will decrease or at a fixed port opening, an increase in pressure drop will allow more mass to pass through it. However, if the pressure drop through the valve is more than 50% of the inlet pressure, then for a fixed port area, more pressure drop will not allow any more mass to to pass through the valve.