The simplicity of this device helps make BCD inspections a fairly easy process, especially when compared to overhauling a regulator. On back inflation BCDs, the valves are also located on the lower portion of the BCD, but may face either the tank or the diver. To use a rear deflation valve, a diver must be in a horizontal swimming position. He simply sticks his rear end up a bit and pulls the over pressure valve release. The simplicity of this device helps make BCD inspections a fairly easy process, especially when compared to overhauling a regulator. OV-540 scuba over pressure valve. Suits all current Aquatec diving BCDs and wings. Coarse thread