Safety Valves in High Pressure Steam Systems

Sizing safety valves after boiler output power in high 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.

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

The tables below can be used for selecting typical safety valves in high pressure systems. Before final design, always consult manufacturing documentation.

Steam Pressure 1000 kPa (10 bar) and 150 psi

Note! The table above is based on high pressure steam of 1000 kPa (10 bar) or 150 psi in imperial units. Latent heat of saturated steam is 1999 kJ/kg (857 Btu/lb).

Steam Pressure 700 kPa (7 bar) and 100 psi

Note! The table above is based on high pressure steam of 700 kPa (7 bar) or 100 psi in imperial units. Latent heat of saturated steam is 2046 kJ/kg (880 Btu/lb).

Steam Pressure 300 kPa (3 bar) and 50 psi

Note! The table above is based on high pressure steam of 300 kPa (3 bar) or 50 psi in imperial units. Latent heat of saturated steam is 2133 kJ/kg (912 Btu/lb).

1 N/m² = 1 Pa = 1.4504 x 10^-4 lb/in² (psi) = 1x10^-5 bar

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