Pressure Instruments – Overrange Protection

Pressure instruments should withstand the maximum operating pressures encountered. Under unusual conditions, such as thermal expansion, the instrument may exceed its range. Most instruments can withstand overpressures up to 1.4 times their maximum range. Instruments exposed to a vacuum should be selected to withstand full vacuum. Certain pressure elements can withstand high overrange. Diaphragm elements with capsules backed up by a metal housing have a high overrange capacity, and many modern electronic pressure transmitters can withstand extreme overpressure. Pressure limiting valves, or “gage savers,” block the inlet pressure at a preset limit, but are rarely used.