Protects the transformer tank from an overpressure generated suddenly or gradually up to a determinate value. (8, 10 or 12 PSI). Relieves the overpressure avoiding that the transformer tank breaks. (14.22 PSI).
The operating principle is that with an increase in pressure in the tank, the valve is pushed out; moving the microswitch needle, pushing the expansion board when a certain level of pressure is reached, and the plate is lifted and evacuates the pressure, closing the contacts of the microswitch.