Calculating Allowable Leakage for air tests on Control Valves

[CarlosEstinos]

Hello All,

I am calculating the allowable leakage for control valves using OEM stated Cv value that is a liquid coefficient.
Using the liquid Cv value, this gives me the allowable leakage as per the specific gravity of the fluid (in this case water)

How can you calculate the allowable leakage of a valve when doing an air test if you are using the liquid flow coefficient?

Any guidance or information would be much appreciated.

Thanks in advance

 

[btrueblood]

You really can't make an exact conversion, the flow regimes for the two leaking fluids are just too far apart. That said, some manufacturers use air testing for leakage because it is a more stringent test (air due to lower density, lower surface tension, and lower viscosity will in general leak at a greater volumetric rate than water), is quicker and easier to run with near zero "cleanup". Some manufacturers may have correlation data that will give equivalent water leak rates for a measured air leak rate, given a particular sealing design geometry and materials.