Step3 First, mean air compressibility is calculated 10 and 20 bara by linear interpolation around the temperature values. For a '4M6' valve suction nozzle is of 4' size and discharge nozzle of 6' size. Referring to the table of standard orifice sizes given in EnggCyclopedia's relief valve sizing calculator.Īvailable valve size is '4M6', which correspond to different nozzle sizes for suction and discharge nozzles of the pressure relief valve. The next higher available orifice area should be selected for the pressure relief valve to be actually installed. Next step is to use the relief valve sizing procedure given in the API part I for critical flow type gas relief valve. Mass flow relieved cannot increase any further, for the given set of flow conditions upstream to the valve. In this case, the actual pressure downstream to the relief valve cannot fall below the critical flow pressure even if much lower pressure exists further downstream to the valve. If the pressure downstream or back pressure of the relief valve is lower than the critical flow pressure, then the flow is said to be of critical type.

For this purpose the critical flow pressure P cf downstream to the relief valve has to be calculated using the following equation from API RP Part I.

The first step is to determine if the flow conditions are critical. The first step is to determine whether the gas flow type is critical or sub-critical. Posts are frequently caught by the spam filter and it may take a few days to notice without contacting one of us.This sample problem for relief valve sizing calculation can be solved in following steps, which are based on pressure relief valve sizing procedures described in API RP Part I.

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Relief valve sizing cases