Safety Valves in Low Pressure Steam Systems

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

The main purpose of the safety valve is to prevent the pressure in the systems to exceed 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 the working (or certification) pressure.

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

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) = 1x10^-5 bar

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

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