Having completed the rEvo rebreather instructor training, I couldn’t resist congratulating myself by equipping my rEvo with a triple dil-oxy-dil offboard block (as they call it in the factory) or a clarinet (as we nickname it).
As you see on the pictures, it integrates well with the unit without compromising the free chest area – this was a primary consideration to me.
The gas block, made out of a solid block of Delrin, has a sound operational feeling. The recessed O2 injection makes it easy to get to the right button, making mistakes by pushing the wrong button fairly unlikely.
Inboard O2 and DIL injection
Although I feel that the usual manual injection buttons on the back are easy to operate, even with several bailout tanks, the manual addition of O2 and DIL by the gas block, with one hand at the front, is really convenient. The injection comes with an easily controlled flow and allows for good pO2 management. The flow rate is comparable to the output of the manual injection in the back: inboard DIL ± 200 L/min at surface, inboard O2 ±- 120 L/min at surface, offboard DIL ± 170L/min at surface.
Offboard gas injection
The possibility of being able to inject offboard gas (ie. gas from a cylinder you or your team carries) was my main reason to get a clarinet. The offboard gas is connected to the gas block by a standard MP hose (like for the BCD). It offers more possibilities to stay on your rebreather in case of loss of inboard DIL or O2.
Also, specific to the hybrid rEvo, you could plug in a hybrid unit (with open orifice and constant MP oxygen regulator) a small tank with oxygen and a variable MP reg. This allows for manual O2 injection by the gas block in the deeper part of the dive (from 80m), where the orifice and the inboard injection (on the constant pressure regulator) would no longer work. In the shallower part however (<80m), you continue having the advantages of the orifice.
Paul advises to flush the gas block after diving by diluent flushing pushing both the diluent and the offboard gas injectors.
Of course the gas block is also an extra possible failure point. A malfunctioning injector could bleed gas in the loop, or one of the connections could leak. I feel that this risk is acceptable and that it can be countered by good awareness and proper training.
I hope this review was helpful to those considering a gas block, and I welcome your opinion or experiences here below.
thinkblue.eu – Sven De Vos