In a significant new patented design, the Poseidon DSV/ADV/BOV Mouthpiece gives you the ability to switch from closed-circuit to open-circuit operation in one simple motion. This compact, switchable mouthpiece is lightweight and easy to breathe from, giving you high performance in both open-circuit and closed-circuit modes. In DSV mode the mouthpiece supports fully closed-circuit bubble free diving with low work-of-breathing. In BOV mode the mouthpiece incorporates a high-performance lightweight open-circuit regulator, based on Poseidon's reliable pilot-operated upstream demand valve design, that allows you to breathe it just like standard scuba. With a simple quarter-turn of an easy-to-operate switch, the mouthpiece switches between DSV (closed-circuit) and BOV (open-circuit) modes.

The mouthpiece also contains a patented system that integrates an automatic diluent addition valve (ADV), which compensates for depth-related compression of the counterlung breathing volume during descents. This ensures a full breath automatically, allowing for hands-free descents. The ADV functionality is incorporated into the mouthpiece with a special mechanism that adjusts the trigger tension on the open-circuit second stage when diving in closed circuit mode, so that gas is only added when the counterlung volume is insufficient to provide a full breath on inhalation.