Pressure difference design before and after the pressure relief valve
Thread Content
There is a valve closing pressure difference between the pressures before and after the pressure relief valve. When determining this pressure difference, it is necessary to consider not only the maximum pressure difference under the process conditions but also whether there is a sufficient margin; what is generally considered to be this margin?
Select the operating pressure of the valve according to the design pressure of the pipeline. Then consider the requirements of the process for cutting. If internal leakage is allowed, select the valve based on the allowable pressure difference for that operating condition ； If internal leakage is not allowed, it should be selected such that the allowable pressure difference equals the operating pressure.
The maximum pressure difference before and after the valve should be determined based on the pressure drop across the entire piping system. If the valve is closed, even if it cannot be closed tightly, but if the pressure behind the valve cannot be maintained, then the minimum pressure value behind the valve needs to be taken into consideration; this requires consideration from the process engineering team, as the instrumentation team may not address it properly. The maximum pressure difference for the control valve in low-pressure pipelines can sometimes be determined based on the pressure before the valve, with little cost involved; however, when the upstream side of the valve is the pump outlet, it is necessary to use the maximum pressure at the pump outlet as a reference. However, in high-pressure pipelines, the above considerations cannot be applied outright; otherwise, the actuator of the control valve will become very large. A comprehensive analysis is necessary, and hasty decisions should be avoided to prevent unnecessary waste.