Solving the water evacuation problem in RBs

zzzzzzzz

Dear List,

It is astounding as to why this issue hasn't been solved. The explanation will be prefaced by the key experimental observation that led to this solution.

As most of you profess to be fastidious with Rebreather cleaning and maintenance, you will be appalled by the following experiment: Replace the exhalation hose with a transparent version. You will notice that water accumulates on the downstream side of the mouthpiece exhalation flapper valve. This comes as no big surprise since many water evacuation strategies help deal with this problem, even if this requires considerable effort, especially when compared to the solution.

What is astounding about this little experiment is that the cleaning products blend with the water and act as surfactants. The result is that water moves through the system in the form of bubble films percolating throught the hoses. This is how the T-pieces are defeated and water is allowed to flow throughout the system. The corrugations in the hoses contribute to the effect by increasing the surface area and creating the transitions that facilitate bubble film creation from the interaction of gas flow and water deposition through condensation.

We can appreciate that the diver in a rebreather acts as a condenser. This is due to the diver being a constant temperature machine. Condensation occurs mainly in the mouth, and flows to the mouthpiece where it accumulates on the downstream side of the flapper.

The solution therefore is to install a tap at this point in the mouthpiece using a barbed fitting and connect it to a positive displacement pump via a thin flexible tube.

The attached image shows how this can be done. The bottom portion of the picture shows the mouthpiece barb fitting with the clear tube. The pump is at the top. The pump has ample capacity to perform this function, and uses spring loaded ball check valves to provide positive cracking pressure. This immobilizes the plunger when not in use. The ring allows the diver to insert a finger for easy actuation and to minimize grasping effort. The pump is usually mounted inverted on the lower right side along the backplate. This allows the pump to be easily actuated while in the swimming position with the arm resting along the body. FYI, the equipment on display is TIG welded 316 SS.

A quick release fitting allows the tubing to be easily disconnected when maintaining the rebreather. The thin tubing anf the finite cracking pressure of the check valves also prevent gas leaks.

The system works quite well, and can be easily fitted to any rebreather. The best analogy is that of the dentist. When the dentist has the vacuum pump in your mouth and asks you to close your mouth, the effect is instantaneous. This pump arrangement is just as effective.

Evacuating the water is as easy as it can be, virtually zero effort, and no annoying percolation sounds. Remember that it only takes a few inches of water to increase the breathing resistance.

Finally, by removing water from the system where it naturally pools before it is allowed to move elsewhere, a reduction in the overall presence and accumulation of water in the system is achieved.

Standard disclaimers apply.

Attached Images

rpump01.jpg (45.6 KB, 151 views)