Valve Selection Guide FAQ
How to choose the right safety or relief valve for your application. Covers sizing, materials, connections, and application-specific guidance.
How do I determine the right valve size?
Valve size depends on three factors: connection size (pipe diameter, typically 1/4 inch to 6 inch), orifice size (determines flow capacity based on required relieving capacity), and set pressure. Use manufacturer capacity charts to match your required relieving capacity (BTU/hr for steam, SCFM for air/gas, GPM for liquids) to the right orifice.
What connection types are available?
Common types include NPT (National Pipe Thread) for smaller threaded valves, Flanged for larger pipes and higher pressures (150# and 300# ratings), Plain/Weld for direct welding, and Tri-Clamp for sanitary applications. Most valves 2 inch and under use NPT. Flanged connections are typical for 2 inch and larger.
What is an orifice designation and why does it matter?
The orifice designation (D, E, F, G, H, J, etc.) identifies the effective discharge area. Larger letters mean greater flow capacity. The orifice must be large enough to relieve your system maximum overpressure scenario. Getting the orifice wrong means the valve cannot protect your equipment.
What seat material should I choose?
Metal-to-metal seats (stainless steel) for steam above 450 degrees F. Soft seats for air, gas, and liquid at lower temperatures with tighter shutoff: Buna-N works to about 250 degrees F, Viton to about 400 degrees F, PTFE to about 450 degrees F. For most air compressor applications, Buna-N is standard.
What body material should I choose?
Brass is most common for air, gas, and water under 406 degrees F and is economical. Bronze offers better corrosion resistance. Carbon Steel handles high-pressure steam and process applications. 316 Stainless Steel is for corrosive media, chemical, or food/pharma environments.
What valve do I need for a boiler?
Boilers require ASME Section I safety valves with a V code stamp (not UV). The valve must be set at or below the boiler MAWP with capacity to relieve full steaming capacity. Aquatrol 740 Series is designed for Section I boiler applications. Section I valves cannot be field-adjusted.
What valve do I need for a pressure vessel?
Pressure vessels require ASME Section VIII safety valves with a UV code stamp. Set pressure must not exceed the vessel MAWP. Use soft-seated valves for air/gas service and metal-seated for steam. Aquatrol 130 Series and 88/89 Series cover most pressure vessel applications.
Need help selecting the right valve? Use our Configure & Price tool or contact us at sales@safetycontrolvalves.com.