High Pressure Steam Systems - Safety Valve Capacities

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

The main purpose for a safety valve is

to prevent the pressure in a system to exceed certification pressure

Above certification pressure no one can guaranty the systems safety - and especially for a steam system with a very hot gas with a huge amount of latent heat the consequence with a failure can be dramatically.

The size of a safety valve depends primarily on the maximum boiler output and the operation pressure of the system. The safety valve must 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 a higher pressure the steam is compressed and requires less volume and the size of the valve can be reduced
for a lower pressure the steam is expanded and requires more volume and the size of the valve is increased

The tables below can be used to select a typical safety valve in a high pressure system. Before the final design - always consult manufacturing documentation.

Steam safety valves capacity chart

Steam Pressure 1000 kPa (10 bar) and 150 psi

High Pressure Steam Systems - Safety Valve Capacities - 10 bar
Pipe Size		Capacity		Maximum Boiler Output
in	DN (mm)	kg/h	lb/h	kW	Btu/h
1/2	15	220	498	122	426 786
3/4	20	472	1 070	262	916 990
1	25	827	1 875	459	1 606 875
1 1/4	32	1 421	3 222	789	2 761 254
1 1/2	40	2 058	4 668	1 143	4 000 476
2	50	3 065	6 954	1 702	5 959 578
2 1/2	65	5 144	11 670	2 856	10 001 190
3	80	7 108	16 124	3 947	13 818 268
4	100	13 694	31 067	7 604	26 624 419

Note! The table above is based on steam with pressure 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

High Pressure Steam Systems - Safety Valve Capacities - 7 bar
Pipe Size		Capacity		Maximum Boiler Output
in	DN (mm)	kg/h	lb/h	kW	Btu/h
1/2	15	159	346	90	304 480
3/4	20	342	743	194	653 840
1	25	599	1 302	340	1 145 760
1 1/4	32	1 030	2 238	585	1 969 440
1 1/2	40	1 792	3 242	1 018	2 852 960
2	50	2 222	4 827	1 263	4 247 760
2 1/2	65	3 730	8 101	2 120	7 128 880
3	80	5 153	11 193	2 929	9 849 840
4	100	9 929	21 566	5 643	18 978 080

Note! The table above is based on steam with pressure 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

High Pressure Steam Systems - Safety Valve Capacities - 3 bar
Pipe Size		Capacity		Maximum Boiler Output
in	DN (mm)	kg/h	lb/h	kW	Btu/h
1/2	15	79	193	47	176 016
3/4	20	169	414	100	377 568
1	25	296	726	175	662 112
1 1/4	32	509	1 248	302	1 138 176
1 1/2	40	737	1 807	437	1 647 984
2	50	1 099	2 695	651	2 457 840
2 1/2	65	1 844	4 522	1 093	4 124 064
3	80	2 547	6 248	1 509	5 698 176
4	100	4 907	12 038	2 907	10 978 656

Note! The table above is based on steam with pressure 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 = 1.4504×10^-4 lb/in² (psi) = 1×10^-5 bar