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# Low Pressure Steam Safety Valves - Capacities

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

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
CapacityMaximum 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

## Related Topics

• ### Design of Control and Safety Valves

Sizing and dimensions of control valves & equipment in steam and condensate systems.
• ### Risk, Reliability and Safety

Risk, reliability and safety in process control systems.
• ### Steam and Condensate

Design of steam & condensate systems with properties, capacities, sizing of pipe lines, system configuration and more.

## Related Documents

• ### Factors of Safety - FOS

Factors of Safety - FOS - are important in engineering designs.
• ### Heating Systems - Safety Valves Size vs. Boiler Power

Safety valves with boilers ranging 275 to 1500 kW.
• ### High Pressure Steam Systems - Safety Valve Capacities

Sizing safety valves according boiler output power in high pressure systems (kW and Btu/hr)
• ### Pilot Operated Safety Valves in Liquid Systems

Calculate pilot operated relief valves in liquid systems.
• ### Safety Relief Valves - Capacity vs. Pressure

Maximum safety valve free air relief capacity.
• ### Safety Signals - Recommended Colors

American National Standards Institutes schedule for safety colors marking physical hazards.
• ### Safety Valve Standards

The most common used safety valve standards in Germany, UK, USA, France, Japan, Australia and Europe.
• ### Safety Valves in Saturated Steam Systems

Calculate safety valves in saturated steam systems
• ### Spring Operated Safety Valves in Liquid Systems

Calculate spring operated relief valves in liquid systems.
• ### Steam Safety Valves - Installation Guide

Guidelines to safety steam valves installation.
• ### Steam Traps - Safety Factors

Selection of steam traps and their safety factors.

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## Citation

• The Engineering ToolBox (2003). Low Pressure Steam Safety Valves - Capacities. [online] Available at: https://www.engineeringtoolbox.com/steam-safety-valves-d_107.html [Accessed Day Month Year].

Modify the access date according your visit.

8.21.8

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