The Zeagle 330-0233, Isolator Valve is installed between any standard Scuba 2nd stage and the end of the LP hose. Sliding the collar on the Isolator Valve, turns the air supply to the 2nd stage on or off. The Isolator Valve is used in situations where it is extremely important that there is no air loss from the 2nd stage, even if the purge button is accidentally pushed on Rebreathers or in tight quarters (such as those found during cave or wreck diving. The picture below shows the Isolator installed on a Zeagle ZX 2nd stage.