![]() K n NAPIER CORRECTION FACTOR FOR SET PRESSURES BETWEEN 15 PSIG AT 10% OVERPRESSUREĮquation K 0 = 01906 P − 1000 02292 P − 1061Ĭourtesy Teledyne-Farris Engineering Co., Cat. K b = vapor or gas flow correction factor for constant back pressures above critical pressure (see Figure 7-26). ![]() K p = liquid capacity correction factor for overpressures lower than 25% for non-code liquids equations only, (see Figure 7-22). ![]() Isentropic coefficient, n, may be used instead of k. If a value is not known the use of k = 1.001, C = 315 will result in a safe valve size. If this factor is not available, compressibility correction can be safely ignored by using a value of Z = 1.0.Ĭ = gas or vapor flow constant, see Figure 7-25. Z = compressibility factor corresponding to T and P. T = inlet temperature ☏ absolute = (☏ plus 460) Below 30 psig set pressure, delta P = P 1 + 3 – P 2. At 10% overpressure delta P equals 1.1 P 1 – P 2. ΔP = Set pressure + overpressure, psig – back pressure, psig. P = relieving pressure in lbs per square inch abs. A specific gravity at any lower temperature will obtain a safe valve size. G = specific gravity of gas (air = 1.0) or specific gravity of liquid (water = 1.0) at actual discharge temperature. V L = required liquid capacity, gal/min (gpm) This is as defined in the ASME Code and ANSI/API Std 526. ):Ī = required orifice area in square inches. Where (Courtesy of Teledyne Farris Engineering Co.
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