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Open any valve catalogue and you will see two rating systems side by side: PN and Class. They describe the same idea — how much pressure a valve can safely hold — but in two different languages. Mixing them up is one of the most common causes of mismatched, leaking or over-specced valves.
PN (short for the French pression nominale, "nominal pressure") is the metric rating used in ISO, EN and DIN standards. The number is the allowable working pressure in bar at 20°C. Common values are PN6, PN10, PN16, PN25, PN40 and PN63. So a PN16 valve is rated for about 16 bar (≈232 psi) at ambient temperature. As the fluid gets hotter, the allowable pressure falls according to a standard rating curve.
Class ratings come from the ASME B16.34 standard, widely used in oil & gas, petrochemical and North American projects. You will see Class 150, 300, 600, 900, 1500 and higher. The number is not a pressure in psi — it is a designation tied to a temperature-pressure table. A Class 150 valve, for example, is rated for about 20 bar (285 psi) at 38°C, but that rating drops as temperature rises.
The trap is assuming "PN16 = Class 150" exactly. At room temperature they are close, but the two systems use different reference temperatures and curves. At higher temperatures the allowable pressures diverge. Always compare the actual pressure-temperature rating for your operating condition, never just the nominal label.
Note: "Approx." because the ratings only line up at specific temperatures. Confirm against the manufacturer's rating curve for your fluid and temperature.
First, follow your piping specification — if the line is built to ASME, use Class; if to ISO/EN/DIN, use PN. Then check the worst-case pressure and temperature (not the average) and pick the rating with margin. When the project mixes standards or the duty is critical, send Reguvale the line conditions and we will confirm the rating and flange standard (e.g. EN1092 vs ASME B16.5) so the valve bolts up first time.
Not exactly. At room temperature PN16 (16 bar) and Class 150 (about 20 bar / 285 psi max at 38°C) are close, but the two systems use different temperature-pressure bases. Always compare the actual pressure-temperature curve for your service, not just the nominal number.
Use PN for projects designed to ISO / EN (DIN) standards, common in Europe, Asia and water/HVAC systems. Use Class (ASME B16.34) for oil & gas, petrochemical and most North American projects. Match the valve rating to your piping specification.
PN25 means a nominal pressure rating of 25 bar (≈363 psi) at 20°C. The allowable working pressure drops as temperature rises, so check the rating curve for your operating temperature.