When describing the nominal pressure of a valve, we often see PN16, PN100, or Class150, Class400. PN and Class are both nominal pressure identification methods for users, but the difference is that they represent the pressure under different temperature, which represents commonly used methods of two “nominal Pressure” system. Among the two commonly used pressure class identification, PN (DIN/GB) refers to the pressure at 120 ℃ corresponding to the pressure, while Class (API) generally refers to the pressure at 454 ℃ corresponding to the pressure.

Pressure Class & PN (Nominal Pressure)

Note: PN is an approximation to the corresponding pressure class, and should not be used as an exact standard.

PN vs. Class

For the valve nominal pressure common identification system, PN is represented by Germany at temperature (120 ℃) as the benchmark, mostly used in ISO, DIN, EN, BS standards. Class (API) is represented by the United States to the temperature of the allowable working pressure as the representative of the temperature – pressure system, mostly used in AMSE and other standards.

The Class series (i.e., pounds) in API valves is calculated according to ASME B16.34 after combining the temperature and pressure for a particular metal. Due to the different temperature reference between the pound class and the nominal pressure, they don’t correspond one to the other. It means that direct pressure conversion is not quite correct in the engineering conversion.

For instance, Class 300 should be 2.1MPa by pressure conversion. But if you consider into the temperature, the corresponding pressure will increase. It is equivalent to 5.0Mpa according to the temperature of the material pressure test measurement.In the meanwhile, other levels are based on 454 ℃ but the Class150 is based on 260 ℃ when in the temperature-pressure system of U.S.