Safety underwater pressure regulator

Provided is an underwater pressure regulator comprising a high and a low pressure chamber, an inlet to the high pressure chamber and at least one outlet port associated with the low pressure chamber. A valve assembly including a valve seat is interposed between the high and low pressure chambers to control the flow of air between the chambers. A coil spring maintains the valve in open position when pressure in the low pressure chamber decreases. An oil reservoir responds to ambient water pressure via a flexible diaphragm to maintain the outlet pressure, i.e., the secondary pressure at a constant level above the ambient pressure at different depths. A piercing member serves to perforate the diaphragm upon excessive expansion of the latter due to high pressure leakage within the regulator system, oil being discharged, under pressure, through the perforated diaphragm, whereupon the regulator then becomes a conventional water-filled unit.