The purge button is the part of a diving regulator that may be depressed manually to force the regulator to deliver air. This is either a separate part mounted in the front cover or the cover may be made flexible and serves as the purge button. Depressing the purge button presses against the diapragm directly over the lever of the demand valve, and this movement of the lever opens the valve to release air through the regulator.
If a second stage is removed from a diver's mouth underwater, it will fill with water. One way of clearing the water is to operate the purge button just before the second stage is replaced in the mouth, or when it is in the mouth, but with the mouthpiece blocked off by the tongue.
Another use is for putting air into a delayed surface marker buoy or lifting bag. Any time that the purge button is operated, the diver must be aware of the potential for a freeflow and be ready to deal with it.
- Brittain, Colin (2004). "Protective clothing, scuba equipment and equipment maintenance". Let's Dive: Sub-Aqua Association Club Diver Manual (2nd ed.). Wigan, UK: Dive Print. p. 35. ISBN 0-9532904-3-3. Retrieved 6 January 2010.
- Brittain, Colin (2004). "Practical diver training". Let's Dive: Sub-Aqua Association Club Diver Manual (2nd ed.). Wigan, UK: Dive Print. p. 48. ISBN 0-9532904-3-3. Retrieved 6 January 2010.