The more gas you have on a dive, the more time you have underwater, and the larger a safety margin you have- although for an oxygen rebreather in a non-overhead environment, it mostly adds to dive time. I wanted to be able to carry not one, but TWO disposable oxygen bottles on a dive, so I went ahead and built a “manifold” based on the MAV components from my previous rebreather.
Here is the MAV 2x in the exploded state. With all brass components, galvanic corrosion, should be kept to a minimum. I may also try nickel plating them after polishing, for even more corrosion resistance. Polishing reduces surface area, which also helps combat corrosion.
At the bottom are a couple of off the shelf mini-oxygen bottle regulators. These have a male (thread) B-sized oxygen fitting on them, for an oxygen hose. Since I want to stick these into a manifold and not have the bottles interfere, I needed a rigid connection that lets the two sets of threads be independent. These fittings are right in the middle- one end is NPT and one end is a female B size fitting (P/N WES-123 for the curious). The NPT end is affixed to the manifold, and then the nuts are tightened onto the regulators. Since the threads are on the nuts, and not on the stem attached to the NPT, the bottles can be in any orientation.
This is very similar to the original MAV, but it has been simplified by putting the MAV directly on the cylinders, which will be front mounted on the diver. This simplifies the gas routing, and eliminates a connection. Another improvement is that the bore for the cartridge valve is not a through hole- this means that the back does not need to be sealed up, eliminating an extra seal.
The cost for the reduced leak path count is that chip evacuation is more difficult in the long hole (roughly 4.25″ x .25″ drill- 17xD hole) and there is an additional, difficult to machine cover that retains the cartridge valve. If this is not installed, the cartridge valve will shoot out of the MAV under pressure. It is definitely an area to watch out for when the valve is pressurized. However, with such a long bore, there is not a good way to be able to machine the valve bore from the reverse side. Fortunately, the cross sectional area of the valve is quite small, so even at 500 PSI, which is the tank pressure, the cover only needs to resist ~50 lbs, across four M3 screws.
Of course, not every dive requires two oxygen bottles, and with no gas installed the inside of the regulator would be filled with water. So that the future rebreather can be operated with just one cylinder, a 1X MAV was produced. Cant wait to try it out!
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