Help needed regarding the maximum allowable pressure drop for control valves
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On our process package, in the data sheet for the control valves, the maximum allowable pressure drop for all control valves is set at the inlet pressure value under normal operating conditions. I think this is problematic, but when I asked others, they said that if the process does not specify this value, then that value should be used anyway. I’m puzzled: if instruments are selected based on this parameter, then if the valve pressure drop becomes too high, flash evaporation will occur in basically all liquid media. I would appreciate it if experienced colleagues could advise me on how to determine the correct maximum allowable valve pressure drop
This post was last edited by Da Chai Shu Sheng on 2009-12-31 at 14:26. The maximum allowable pressure drop is determined from a safety perspective; that is, the pressure drop experienced by the valve must not exceed this value. It is not taken into account in the actual calculations, but it is used in selecting the actuator (the torque output of the actuator is calculated using this value). Since there is a pressure before the valve and a pressure after it, the actual pressure difference can be determined. What is actually used in the calculations is this actual pressure difference. Moreover, as long as the outlet pressure is not lower than the saturated steam pressure, flashing will not occur.
In simple terms, the allowable maximum pressure drop is the pressure that the valve can withstand when it is completely closed; in other words, there is no pressure behind the valve, only pressure in front of it. So the allowable maximum pressure drop is the pressure before the valve.
The third floor said it very well; give the third floor top marks!