Older Pressure Relief Devices
Older pressure relief devices have a diaphragm and a relief pin that is destroyed each time the device operates and must be replaced.
Replacement parts of an older pressure relief device must be replaced with exact duplicate parts; otherwise, the operating relief pressure of the device will be wrong.
The relief pin determines operating pressure; a number, which is the operating pressure, normally appears on top of the pin. Check your specific transformer instruction manual for proper catalog numbers. Do not assume you have the right parts or that correct parts have been previously installed—look it up. If the operating pressure is too high, a catastrophic tank failure could result. On older units, a shaft rotates, operates alarm/trip switches, and raises a small red flag when the unit releases pressure. If units have been painted or are more than 30 years old, they should be replaced with the new model as soon as it is possible to have a transformer outage. Once each year, and as soon as possible after a through-fault or internal fault, examine the indicator flag to see if the device has operated. The flags must be examined from a high-lift bucket if the transformer is energized. A clearance must be obtained to test, repair, or reset the device. See the instruction manual for your specific transformer. Test alarm/trip circuits by operating the switch by hand.
Check to make sure the correct annunciator point activates. Every 3 to 5 years, when doing other maintenance or testing, examine the top of the transformer tank around the pressure relief device. If the transformer has a conservator and oil is visible, the device is leaking, either around the tank gasket or relief diaphragm. The gasket and/or device must be replaced. Before ordering, make sure that the new device will fit the same tank opening. Most devices are made by the Qualitrol Company; contact the manufacturer to obtain a correct replacement.