Basis of sizing compressor Surge control valve
Basis of sizing compressor Surge control valve
(OP)
I am trying to understand on what basis is a centrifugal compressor surge control valve sized. So far I have seen the following basis:
a) 1.8 to 2.2 times the CV at surge control line
b) 0.9 to 1.1 times CV calculated at intersection of horizontal line from design point with 105 % speed.
c) Valve sized for design control point
As all of the above provide different CV values, is there an industry standard? or are there more rules of thumb than I have looked at.
a) 1.8 to 2.2 times the CV at surge control line
b) 0.9 to 1.1 times CV calculated at intersection of horizontal line from design point with 105 % speed.
c) Valve sized for design control point
As all of the above provide different CV values, is there an industry standard? or are there more rules of thumb than I have looked at.





RE: Basis of sizing compressor Surge control valve
perhaps you should make inquiries to other surge control system mfg's for their recommendations. also, different valve mfg's provide Cv values for their valves. Oh! other considerations are actual operating modes for the compressor (i.e. start-up, normal mode, process upset, min/max flow/pressure conditions, shutdown, predicted frequencies for any previously stated conditions, etc.). the case may be where major process upset condition may frequently(?) be expected/predicted, thus the user/operator may need a larger valve (Cv) to adequately meet those requirements.
sorry, i am not familiar with other industry stds, but i hope the aforemention information is helpful. each application is unique and sometimes requires careful and meticulous thought.
feel free to respond and good luck!
-pmover
RE: Basis of sizing compressor Surge control valve
A system with an undersized valve is never capable of preventing surge and could lead to damage. However a greatly oversized valve (bigger is never better) could result in a choked flow condition at the very worst or an unstable operation in general.
The most common approach I think is to use 1.8 to 2.2 times the calculated Cg calculated at the point on the operating curve where the surge line intersects the max speed performance curve.
BTW, the speed of response is also important in the selection of the controller and process transmitters. For the later we never use the Rosemount smart transmitters in this application.