Maximum Isentropic Flow of Dry Saturated Steam Through Pressure Relief Valves

The maximum isentropic flow of dry saturated steam using iterative computer techniques with standard (ASME) steam property data is determined. Comparison of this maximum flow with the Napier flow (the calibrating ideal flow for ASME pressure relief valve capacity ratings) reveals significant divergence between the two. A correction factor is developed to be applied to existing ASME safety and safety relief valve capacity ratings to rectify the difference. Experimental flow measurement work verifying the divergence between the maximum isentropic flow and the Napier flow is described.