PN

   a symbol for "nominal pressure," a measure used for rating piping, valves, fittings, etc. Nominal pressure is essentially the pressure rating of the piping system, measured in bars at a temperature of 20 °C (68 °F). (One bar equals 100 kilopascals or approximately 14.5038 pounds per square inch in traditional English units.) Industrial standards organizations, such as the American National Standards Institute (ANSI), set standards for pipes and fittings based on PN ratings; these standards specify in detail the size, composition, and strength of each component.