PSV sizing calculator – fire case for liquid filled vessel

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Pressure Safety valve sizing calculator for fire case for a liquid filled vessel. This calculators should be used when gas resulting from boiling of the liquid is discharged through the safety relief valve.

Vessel Diameter m
Vessel Length (TL-TL) m
Vessel height above ground m
Liquid level in the vessel (HHLL-TL) m
Vessel Orientation
Type of head
Area considered for calculation
Environmental Factor
Set pressure barg
Accumulation %
Back pressure barg
Coefficient of discharge Kd (max=0.975)
Rupture disk upstream to PSV ?
Is released fluid steam ?
Relieving temperature 0C
Relieved Vapor Desnity kg/m3
Isentropic coefficient (Cp/Cv)s
Moleculare weight
Compressibility factor (Z)
Latent heat of vaporization kcal/kg
Relieving pressure barg
Exposed area m2
Minimum orifice area requirement cm2
Gas flowrate to be relieved kg/hr

The calculated area is the minimum orifice area required to allow the discharge of gas. The actual orifice area is the next higher available area. Following table presents the standard orifices with their designating letters and corresponding area.

Area (cm2) Designating letter Valve size (inch)
0.71 D 1D2 / 1.5D2 / 1.5D3
1.26 E 1E2 / 1.5E2 / 1.5E3
1.98 F 1.5F2 / 1.5F3
3.25 G 1.5G3 / 2G3
5.06 H 1.5H3 / 2H3
8.3 J 2J3 / 3J4
11.86 K 3K4 / 3K6
18.49 L 3L4 / 4L6
23.2 M 4M6
28 N 4N6
41.2 P 4P6
71.2 Q 6Q8
103 R 6R8 / 6R10
168 T 8T10


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