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Safety Valves in High Pressure Steam Systems

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

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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 Pressure 1000 kPa (10 bar) and 150 psi

Pipe SizeCapacityMaximum Boiler Output
inDN (mm)kg/hlb/hkWBtu/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

Pipe SizeCapacityMaximum Boiler Output
inDN (mm)kg/hlb/hkWBtu/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

Pipe SizeCapacityMaximum Boiler Output
inDN (mm)kg/hlb/hkWBtu/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 x 10-4 lb/in2 (psi) = 1x10-5 bar
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