Nominal pressure is a reference value for a piping system.
It is specified according to DIN, EN, ISO by the designation PN ( pressure Pressure (gauge pressure) Pressure for which the value is equal to the algebraic difference between the absolute pressure and the atmospheric pressure. nominal) followed by a dimensionless integer indicating the design pressure Design pressure Design pressure is the maximum pressure for which the system or component was designed for continuous usage. in bar at room temperature (20 °C).