Coffee Break Training: Automatic Sprinklers: Aboveground Sprinkler Pipe Air Pressure Changes [open pdf - 485KB]
"Dry pipe and double interlock preaction sprinkler systems should be subjected to a 24-hour air pressure leakage test at 40 pounds per square inch (2.8 bar) before they are placed in service or after significant changes to the pipe network. The pressure readings often are recorded from the Bourdon gauges that are mounted on the sprinkler riser. A Bourdon gauge is made of a hemispherical tube that is linked to a small, internal coiled spring. As the pressure changes in the tube (due to temperature or water pressure changes), the internal spring is either loosened or more tightly coiled. An attached pointer or needle moves across the face of the gauge where air or water pressure is calibrated."
Coffee Break Training - Fire Protection Series No. FP-2013-17
United States Fire Administration: http://www.usfa.fema.gov/