Questions about safety valves
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When calculating the relief volume of a safety valve in a calculation sheet, how should the value of the liquid’s vaporization potential q be determined at the relief pressure?
The heat of vaporization under discharge conditions is used, as the relief by the safety valve occurs under such conditions; the discharge pressure is higher than the setting pressure, so the temperature is naturally different from the operating temperature. To be precise, the heat of vaporization released varies due to the presence of overpressure. Chapter 8 of the standard HG-T 20570.2-95 \"Installation and Selection of Safety Valves\" specifies the heat of vaporization under discharge conditions in case of a fire. Since the heat of vaporization decreases as temperature rises, it is most appropriate to use the value of heat of vaporization at the maximum discharge pressure (set pressure plus maximum overpressure). However, considering that the actual discharge area is an integer multiple of the calculated area, the heat of vaporization under the triggering condition can be used directly.