×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

How much critical is molecular weight for pressure control valve

How much critical is molecular weight for pressure control valve

How much critical is molecular weight for pressure control valve

(OP)
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?

RE: How much critical is molecular weight for pressure control valve

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.

RE: How much critical is molecular weight for pressure control valve

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.  

RE: How much critical is molecular weight for pressure control valve

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.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources