BQX System Outline


Canadian homebuilder, Gordon Smith, has proven that a good idea and can be more than just a garden shed project. The Jetsam Technology KISS rebreather is fast becoming one of the most popular rebreathers for recreational divers. It works on a very simple system:
  • There is a standard loop consisting of axial scrubber, split, back-mounted counterlungs and a DSV. Added to this is a ppO2 monitoring system: no thinking, no control, just a simple monitoring system.
  • Diluent is added by an ADV.
  • Oxygen is replaced as it is metabolized by a constant flow of pure oxygen.
  • Oxygen can be manually added occasionally as it is required through a by-pass valve.
It is essentially a closed-circuit rebreather which requires the occasional intervention by the diver. The diver cannot relax and "just breathe" but then, what kind of rebreather diver would want to? The Inspiration is fully automatic and yet there have been many fatalaties. Not that I am criticising the Inspiration, only that automation is not necessarily a good thing.

The BQX is based on the KISS idea. However, it is limited by depth. The KISS oxygen regulator is a standard Apeks regulator with a delrin blanking disk to isolate it from ambient pressure. In a normal regulator, the first stage uses water pressure to regulate its outlet (interstage) pressure (known as the IP) to 8-10bar above ambient pressure. For example, at 30m a normal regulator would be supplying gas at 8-10bar above ambient pressure (4bar) i.e. 12-14bar. At 50m this would increase to 14-16bar.

On the KISS, as depth increases the flow of oxygen has to decrease because the oxygen becomes more dense. The 1st stage is therefore blanked off from ambient pressure. This means a constant supply of 8-10bar, not 8-10br above ambient. If the regulator is set to 9bar for example, then at 80m the regulator pressure (the IP) will equal the ambient pressure and the flow of oxygen will stop. That oxygen needs to be replaced. There are a number of options available to the diver, like supplying oxygen manually. Juergensen Marine has developed an electronically controlled oxygen addition valve which would enable a normal regulator to be used for oxygen addition, essentially eliminating the depth restriction. But to me, that is also eliminating the strength of the KISS, its simplicity. My plan for the BQX, which may be totally wrong, is to have it change from closed- to semi-closed circuit at its cut-off depth. The amount of diluent that would need to be added at 90m to maintain a decent ppO2 would be minimal at the surface. The use of a metering valve on the diluent would mean that the oxygen feed would work up to the cut-off depth, the small flow of diluent would be negligible until the depth had increased. It should also enable a standard regulator to be used on the diluent side too. But this is a long way off and may be entirely theoretical. There are many more hurdles to get over before I need to worry about using the BQX on a deep dive. Chances are that I'll be so bored by then that I will end up buying a KISS anyway.
 

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