Pressure rating is the single most misunderstood number on a valve nameplate, and the source of many wrong orders. A PN16 valve and a Class 150 valve look similar at room temperature, but they come from different standards systems, behave differently as temperature rises, and must match the flange standard on your line. This guide explains what pressure rating really means, how PN and Class compare, and what to check before you place an order.
What Pressure Rating Actually Means
A valve pressure rating is not the maximum pressure the valve can hold at any temperature. It is a reference value defined at a baseline temperature: room temperature for DIN/EN PN ratings, and 100°F / 38°C for ANSI/ASME Class ratings. As temperature rises, the allowed working pressure drops, and every standard publishes a pressure-temperature (P-T) curve for this purpose. When you specify a valve, always state both the design pressure and the design temperature together.
The PN System (DIN / EN)
The PN system (from the German Nenndruck, nominal pressure) is used across Europe, China and most of the world. PN values are round nominal pressures in bar at the reference temperature: PN6, PN10, PN16, PN25, PN40, PN63 and so on. A PN16 valve is rated for about 16 bar at room temperature. PN does not map linearly to temperature: at 200°C a PN16 cast-iron valve may safely hold only around 10 bar, and at 300°C even less.
The ANSI / ASME Class System
The Class system (ANSI/ASME B16.34) is used in the USA and by many international oil and gas projects. Class values are not pressures in bar or psi: Class 150, 300, 600, 900, 1500 and 2500 are logarithmic steps defined by flange bolt patterns. At room temperature Class 150 body ratings for stainless steel roughly sit around 19-20 bar, but at 400°C the same Class 150 flange may be limited to about 5 bar. Never read "Class 150" as "150 psi" for a stainless steel body; always consult the P-T table for the actual material.
Quick Comparison (Approximate, at Room Temperature)
| DIN/EN PN | Approx. ANSI Class | Approx. bar (room temp, stainless) |
|---|---|---|
| PN10 | Class 125 / 150 (wcb) | ~10 bar |
| PN16 | Class 150 | ~16-20 bar |
| PN25 / PN40 | Class 300 | ~25-40 bar |
| PN63 / PN100 | Class 600 | ~63-100 bar |
These are approximations for quick orientation only. PN and Class are different standards families with different flange drilling and different P-T curves; there is no exact interchange. When in doubt, ask the manufacturer for the specific P-T table of the valve body material you are buying.
Temperature Changes the Rating
- Carbon steel (WCB / A105) loses allowed pressure steadily above 200°C and is usually limited below 425°C
- Stainless steel (CF8 / CF8M, 304/316) holds rating to higher temperatures, but soft seats (PTFE, RPTFE) become the limiting part above 200-250°C
- Cast iron is limited to lower temperatures and pressures and is unsuitable for steam above about 200°C
- Alloys for high temperature (WC6, WC9, F11, F22) are specified with their own Class ratings for boiler and superheater service
Common Buying Mistakes
- Mistake 1: reading Class 150 as "150 psi" and under-rating the valve at high temperature
- Mistake 2: buying PN16 to replace Class 150 without checking flange drilling — the bolt circles and numbers differ, so the flanges will not mate
- Mistake 3: rating by room temperature only, then being surprised when the seat or body rating at operating temperature is lower
- Mistake 4: ignoring the seat material temperature limit — a body rated for 40 bar is useless if the PTFE seat melts at 180°C
Ask a Manufacturer Before You Spec
Langtuo Valve, a Shenzhen-based manufacturer founded in 2009, supplies ball, gate, globe, butterfly, check and control valves in GB, API, ANSI and DIN standards to export customers in more than 30 countries. Every batch ships with a documented test report, and our technical team can confirm the pressure-temperature rating and suitable materials for your exact steam or pressure application. Send your specification (size, pressure, temperature, medium) through the contact page or by email, and we will reply within one business day.
Pressure rating is the single most misunderstood number on a valve nameplate, and the source of many wrong orders. A PN16 valve and a Class 150 valve look similar at room temperature, but they come from different standards systems, behave differently as temperature rises, and must match the flange standard on your line. This guide explains what pressure rating really means, how PN and Class compare, and what to check before you place an order.
What Pressure Rating Actually Means
A valve pressure rating is not the maximum pressure the valve can hold at any temperature. It is a reference value defined at a baseline temperature: room temperature for DIN/EN PN ratings, and 100°F / 38°C for ANSI/ASME Class ratings. As temperature rises, the allowed working pressure drops, and every standard publishes a pressure-temperature (P-T) curve for this purpose. When you specify a valve, always state both the design pressure and the design temperature together.
The PN System (DIN / EN)
The PN system (from the German Nenndruck, nominal pressure) is used across Europe, China and most of the world. PN values are round nominal pressures in bar at the reference temperature: PN6, PN10, PN16, PN25, PN40, PN63 and so on. A PN16 valve is rated for about 16 bar at room temperature. PN does not map linearly to temperature: at 200°C a PN16 cast-iron valve may safely hold only around 10 bar, and at 300°C even less.
The ANSI / ASME Class System
The Class system (ANSI/ASME B16.34) is used in the USA and by many international oil and gas projects. Class values are not pressures in bar or psi: Class 150, 300, 600, 900, 1500 and 2500 are logarithmic steps defined by flange bolt patterns. At room temperature Class 150 body ratings for stainless steel roughly sit around 19-20 bar, but at 400°C the same Class 150 flange may be limited to about 5 bar. Never read "Class 150" as "150 psi" for a stainless steel body; always consult the P-T table for the actual material.
Quick Comparison (Approximate, at Room Temperature)
| DIN/EN PN | Approx. ANSI Class | Approx. bar (room temp, stainless) |
|---|---|---|
| PN10 | Class 125 / 150 (wcb) | ~10 bar |
| PN16 | Class 150 | ~16-20 bar |
| PN25 / PN40 | Class 300 | ~25-40 bar |
| PN63 / PN100 | Class 600 | ~63-100 bar |
These are approximations for quick orientation only. PN and Class are different standards families with different flange drilling and different P-T curves; there is no exact interchange. When in doubt, ask the manufacturer for the specific P-T table of the valve body material you are buying.
Temperature Changes the Rating
- Carbon steel (WCB / A105) loses allowed pressure steadily above 200°C and is usually limited below 425°C
- Stainless steel (CF8 / CF8M, 304/316) holds rating to higher temperatures, but soft seats (PTFE, RPTFE) become the limiting part above 200-250°C
- Cast iron is limited to lower temperatures and pressures and is unsuitable for steam above about 200°C
- Alloys for high temperature (WC6, WC9, F11, F22) are specified with their own Class ratings for boiler and superheater service
Common Buying Mistakes
- Mistake 1: reading Class 150 as "150 psi" and under-rating the valve at high temperature
- Mistake 2: buying PN16 to replace Class 150 without checking flange drilling — the bolt circles and numbers differ, so the flanges will not mate
- Mistake 3: rating by room temperature only, then being surprised when the seat or body rating at operating temperature is lower
- Mistake 4: ignoring the seat material temperature limit — a body rated for 40 bar is useless if the PTFE seat melts at 180°C
Ask a Manufacturer Before You Spec
Langtuo Valve, a Shenzhen-based manufacturer founded in 2009, supplies ball, gate, globe, butterfly, check and control valves in GB, API, ANSI and DIN standards to export customers in more than 30 countries. Every batch ships with a documented test report, and our technical team can confirm the pressure-temperature rating and suitable materials for your exact steam or pressure application. Send your specification (size, pressure, temperature, medium) through the contact page or by email, and we will reply within one business day.