Low Pressure Steam Safety Valves - Capacities

Sizing safety valves after boiler output power in low pressure systems (kW and Btu/hr).

Sponsored Links

The main purpose of a safety valve is to prevent the pressure in a system to exceed the certification pressure. Above certification pressure, no one can guaranty the systems safety - and especially for a steam system with very hot gas with huge amount of latent heat, the consequences can be dramatically.

The size of the safety valve depends primarily on the maximum boiler output and the operation pressure of the system. The safety valve shall as minimum have the evacuation capacity of all the vapor the boiler can produce running at full power at working (or certification) pressure.

The table below can be used to select a typical safety valve based on boiler output. Before final design, always consult the manufactures documentation.

Low Pressure Steam Safety Valves - Capacities
Pipe Size DN		Capacity		Maximum Boiler Output
(in)	(mm)	(kg/h)	(lb/h)	(kW)	(Btu/h)
1/2	15	38	86	23	81 270
3/4	20	82	185	50	174 825
1	25	145	324	89	306 180
1 1/4	32	249	557	152	526 365
1 1/2	40	360	807	220	762 615
2	50	536	1 199	328	1 133 055
2 1/2	65	901	2 012	551	1 901 340
3	80	1 244	2 779	761	2 626 155
4	100	2 397	5 355	1 465	5 060 475

Note! The table above is based on low pressure steam of 100 kN/m² (1 bar) or 15 psi in imperial units. Latent heat of saturated steam is 2201 kJ/kg (945 Btu/lb).

1 N/m² = 1 Pa = 1.4504 x 10^-4 lb/in² (psi) = 10^-5 bar

For higher pressure, steam is compressed and require less volume - required size of the valve reduced
For lower pressure, steam is expanded and require more volume - required size of the valve increased

Capacity of low pressure steam safety valves chart