Nominal pressure is a reference value for a piping system.
It Pressure/vacuum relief valve Pressure/vacuum relief valve is an umbrella term that includes pressure or vacuum relief valve as well as pressure and vacuum relief valve. is specified according to DIN, EN, ISO by the designation PN (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).