Bailout valves

Switchable mouthpieces for rebreathers.

A Bail Out Valve (BOV) is a Diver Surface Valve (DSV) that has a second stage regulator incorporated into the mouthpiece and is connected to either the onboard diluent tank or the off board bailout tank. In this way the diver has a supply with open circuit breathing gas.

In our rebreather training we all learn the phrase: In case of doubt? Bailout! It must be noted, however, that often a gasproblem can be prevented by flushing. Bailout mouthpieces are rebreather mouthpieces that can be switched to open circuit breathing with a simple action. This is necessary if there is a malfunction in the rebreather or if a temporary sanity break* is required. Rebreather malfunctions come in different forms:

– The entry of water into the loop, so that the scrubber no longer functions

– Massive water entry through a leak or a crack

– Too high a partial oxygen pressure

– Observation of too low partial pressure of oxygen

– Hyperoxia due to shallow breathing, bad gas composition, bad scrubber resulting in dizziness or muscle tension around the mouth or even unconsciousness

– Switching to another cylinder due to gas shortage

– temporarily wanting to breathe a different mixture

Most rebreather divers initially use a separate open circuit regulator mounted on their sidemount cylinder. In practice, however, it takes time and sometimes effort to switch from the normal rebreather mouthpiece, which must first be closed, to the OC regulator in emergency situations. A good bailout mouthpiece can be operated with one hand. It offers security and comfort in the situations mentioned above.

Another big advantage is the possibility to intervene as a buddy and put a diver in distress on open circuit with a simple action.

A special consideration is the choice to connect the OC-BOV to the on-board diluent cylinder or to the off-board cylinder. A defensible choice is to connect the BOV to the onboard, if the sitemounded cylinders also have automatics mounted on them. This gives an extra redundancy whereby the rebreather with a small diluent supply is used for the first emergency. After this, it is easy to return to the circuit or switch to OC bailout. There are many opinions and views on this, but think carefully about this choice.

*Sanity break = easy temporary OC breathing to solve a problem.

The bailout valves shown above are a selection of the many models that have been developed for sport and military rebreathers over the last 20 years. If you have pictures of older or newer models, I would be happy to add them to the page. Please send the picture in the highest possible resolution with technical data! Your contribution is highly appreciated!