The function of the Pressure Indicator is to provide visual indication in the event of a rupture disc burst. If the disc has ruptured, the pressure relief valve will have discharged and must be replaced. (refer to Sentry safety device information). Applications The G16 and G20 Pressure Indicators are intended to be used as part of the Henry Sentry safety device assembly. The units are suitable for use with HCFC, HFC, HFO, CO2 and ammonia refrigerants, along with their associated oils.