This simple skill is performed so that you will have some first-hand experience of a freeflow (rushing of gas) from the mouthpiece of your regulator’s second stage. This event is rare if regulators are serviced regularly by certified regulator technicians, but sometimes, things happen. You should know what to do if it should happen to you.
To simulate freeflow, start by tilting your head down to the right, and with your finger, press down on the purge button to simulate the freeflow of gas for 15 seconds, and breathe normally. Then check your pressure gauge. Always keep a reserve of 50 bar/750 psi of air so that, with proper planning, you can make a comfortable ascent. (Note: On pressure gauges, the closest reading you could see is 50 bar/700 psi.)
If your mouthpiece freeflows during a dive, you now know how to breathe from it. It is best to secure your buddy’s AAS because your air will escape quite fast through the freeflow. Check your air pressure, signal your buddy or dive professional, and ascend.
You may also be asked to shut down your tank during a simulated freeflowing regulator drill. Attempt this only when breathing from your buddy’s donated long hose (AAS).