multiregulator

When diving with a rebreather, or on open circuit SCUBA to great depths, it's common practice to carry one or more tanks with different gas mixes in, due to the issues of Nitrogen narcosis (shallow) and Oxygen toxicity (deeper). Use of the wrong mix at the wrong depth can cause hypoxia or hyperoxia, both dangerous conditions. Normally, multiple DVs (Demand Valve, the mouthpiece) are used, one for each cylinder. In an emergency situation, especially after a sudden loss of main gas supply and/or in a dark/murky environment, picking the wrong DV could be dangerous especially if it goes unnoticed.

The proposed regulator is a long cylinder containing a plunger, with a sealed chamber at one end and the other open to the surrounding water. As the external pressure increases, the gas in the sealed chamber is compressed, and the plunger moves down the cylinder. The position of the plunger can be determined for a range of pressures. The end of the plunger reaches through the sealed chamber and is attached to the line to the DV. The plunger is hollow, with the top end (facing the water) sealed and a narrow ring near the top connected to the central cavity. At points down the cylinder, openings in the walls connect to the first stage regulators atop the various cylinders.

As the diver descends, the plunger moves down the cylinder, moving the opening to the DV between the outlets for the various cylinders. When the diver needs to breath from one of the cylinders rather than his/her primary source, s/he simply needs to breath from the DV, which will be connected to the correct gas mix for the current pressure.

While the described mechanism uses an unsprung plunger, a spring assist or diaphragm-actuated mechanism could also be used. The core of the idea is a valve that changes inputs dependant on external pressure.