Dear All,

DEP 31.38.01.11-Gen (February 2012), Section 2.3.4, states that for slow valve closing speed surge pressure can be calculated as below:

P_surge = (0.02 * L * density * fluid_velocity * valve_closure_speed) / DN

where L is the piping lenght between pump and valve and DN the nominal diameter in pipe.

The same section states as below:

"The maximum surge pressure develops when the valve closes rapidly relative to the piping lenght. Using SI units, the maximum surge pressure is calculated by the Joukovski formula:

P_surge = system_sonic_velocity * density * fluid_velocity "

I tried to use both formulas, and Joukovski yields a higher value of surge pressure. With such value my system fails, whereas with the surge pressure I get from the first formula the system pass.

Since the slow valve closing speed is exactly my case, do you think I can use the first formula rather then Joukovski even if it's less conservative?

Thank you for your valuable opinion.