Class 150 vs Class 300 Valve
Pressure-Temperature Ratings, Flange Dimensions & How to Choose the Right Class
What Does Valve "Class" Actually Mean?
"Class 150" and "Class 300" are ANSI/ASME B16.34 pressure classes that define a valve and its flanges' allowable pressure at a given temperature — they are not the literal pressure rating in bar or psi. The actual allowable pressure depends on both the class and the material, and it drops as temperature rises.
Specifying the wrong class either over-engineers your piping (unnecessary cost and weight) or under-rates it (a safety risk). This guide compares Class 150 and Class 300 valves so you can confirm the right class against your project's design pressure and temperature.
Class 150 vs Class 300 — Side by Side
| Parameter | Class 150# | Class 300# |
|---|---|---|
| Approx. rated pressure (ambient, WCB) | ~19.6 bar / 285 psi | ~51 bar / 740 psi |
| Flange thickness | Thinner | Thicker — roughly 1.4–1.6x Class 150 |
| Bolt circle diameter | Smaller | Larger, for the same nominal size |
| Number of bolt holes | Fewer | Equal or more, larger bolt size |
| Typical use case | Utility water, low-pressure process lines | Higher-pressure process, steam, refinery lines |
| Cost | Lower | Higher, due to more material and machining |
| Weight | Lighter | Heavier for the same nominal bore |
Figures shown are approximate, for Carbon Steel (ASTM A216 WCB) at ambient temperature, per ASME B16.34. Always confirm exact ratings for your material and operating temperature before finalizing a specification.
Class 150 Is Usually Right For…
- Utility water and low-pressure service lines
- HVAC, plumbing, and fire-fighting systems
- Cooling water circuits and general plant utilities
- Projects where the piping class specifies 150# flanges
Class 300 Is Usually Right For…
- Higher-pressure process and refinery piping
- Steam lines and boiler feed systems
- Oil & gas transmission lines with elevated design pressure
- Projects where the piping class specifies 300# flanges
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Frequently Asked Questions — Class 150 vs Class 300
Class (also written 150# or 300#) refers to the ANSI/ASME B16.34 pressure-temperature rating class of the valve and its flanges. It is not a literal pressure number — the actual allowable pressure depends on the material and operating temperature, per the ASME B16.34 rating tables. Higher class numbers mean the valve is rated for higher pressure at a given temperature.
For carbon steel (A216 WCB) at ambient temperature, Class 150 is rated to roughly 19.6 bar (285 psi) and Class 300 to roughly 51 bar (740 psi). Both ratings drop as temperature rises — always check the ASME B16.34 pressure-temperature table for the exact material and temperature you are working at, rather than relying on the class number alone.
No. Class 300 flanges are thicker, have a larger bolt circle, more bolt holes, and often a different gasket face than Class 150 flanges of the same nominal size. They are not physically or dimensionally interchangeable — mating flange class must match on both sides of a joint.
Class selection depends on your line's design pressure and design temperature, as specified in your piping class or P&ID. As a rule of thumb, utility and low-pressure water lines commonly use Class 150, while higher-pressure process, steam, and refinery lines often require Class 300 or higher. Always confirm against your project's piping specification rather than assuming.
Yes. We supply Gate, Globe, Ball, Butterfly, and Check Valves in Class 150#, 300#, 600#, and higher, in Cast Iron, Carbon Steel, Stainless Steel, and Alloy Steel, with hydrostatic test certificates and material test reports on request.