What is the nominal pressure class of a valve?

Class：

A combination of letters and numbers used to identify the pressure/temperature capability of a valve in relation to the mechanical and dimensional properties of the valve material. It consists of the letter Class followed by a dimensionless integer. The number following the letter Class does not represent a measured value and should not be used in calculations. The permissible pressure of piping elements depends on the Class value, the material and the permissible working temperature, unless otherwise specified in the respective standard. The permissible pressures are given in the pressure-temperature rating tables of the respective standards.