GB/T 1048-2005 "Definition and Selection of Piping Components PN (Nominal Pressure)" is defined as follows:
Nominal Pressure: An alphanumeric designation for reference purposes related to the mechanical and dimensional characteristics of a piping system element, consisting of PN followed by a dimensionless number.
Nominal pressure and nominal size are one of the important parameters when carrying out valve technical design -
Unless otherwise specified, the number following the nominal pressure PN does not represent a measured value and is not used for calculation purposes.
The allowable pressure of pipeline components depends on the PN value, material and design of the component, and the allowable operating temperature. The allowable pressure value is given in the pressure and temperature grade table of the corresponding standard.
In engineering applications, the CLASS (CL) pressure level system of Britain, the United States and other countries and the K-level system of Japanese standards are often used. CLASS (CL) pressure level consists of the letters "Class" followed by a dimensionless integer number. The number following "Class" is the same as PN and does not represent a measured value and is not used for calculation purposes. The allowable pressure value depends on the valve material and application temperature. The specific value depends on the pressure-temperature rating table. Since the temperature bases of the nominal pressure PN and CL pressure levels are different, there is no strict correspondence between them.
