Critical Properties and Control Valve Sizing 1

[tkdhwjd]

Please pardon my ignorance.
But can anyone please explain to me why critical pressure and temperature data are required to size the control valve? Thanks!!

 

[TD2K]

I haven't had to supply the critical temperature for my instrumentation people but they do want the critical pressure. Fisher (at least) uses the vapor pressure and the critical pressure to calculate what they call a cavitation index and they use that to determine what portion of the actual pressure drop is used for valve sizing.

http://www.rosemount.com/document/index.html

has a control valve handbook somewhere there (couldn't find it, sorry) that is an excellent book to review.

 

[TD2K]

Found it

http://www.documentation.frco.com/groups/public/documents/book/cvh99.pdf