CAVITATION DUE TO VALVE CLOSURE

[tmc1]

The problem I face in plant is to determine the maximum angle of closure from full open before the valve starts to cavitate. I am working on a project to implement partial stroke test on valve on-line and need to determine to what max. angle the valve is allowed to stroke before cavitation kicks in. The fluid is hydrocarbons like isobutane and hexene-1. Any software programs that can do this job? Appreciate comments or guidance. Thanks.

Rgds,
Chng,TM

 

[stanier]

Try the Tyco water software.

 

[quark]

I think it may be possible if you know the temperature of the fluid and pressure drop across the valve at each position. You have to check that the (line pressure-the pressure drop) should always be more than the saturation pressure of the fluid at the fluid inlet temperature.

Regards,


Eng-Tips.com : Solving your problems before you get them.

 

[JNieuwsma]

The Crane TP-410 software might also be helpful. I'm not sure if the current version can handle partially closed valves. Available at

http://www.cranvalves.com

Jonathan Nieuwsma

 

[Scotsinst]

Cavitation is a function of pressure drop, downstream pressure, vapor pressure and valve pressure recovery factor.
The valve pressure recovery factor is highest for wide open valve (Fl, Kc is lowest) so closing the valve more will not cause cavitation in itself.
What causes the cavitation is the system hydraulics; when you close the valve the downstream pressure falls and cavitation occurs.
You just need to calculate the downstream pressure at different valve openings (different Cv's) and using the pressure recovery factor for these openings, calculate the onset of cavitation. You can use Fisher First or other commercial control valve software from Masoneilan, Valtek etc.
By the way, most partial stroke tests to verify operability (for safety system testing) for clean fluids use 10% as the stroke which normally would not cause any problems with upsetting the process flow).