Inline Shut-Off Valves
The Oxygen Shutoff Is a Mixed-Bag
Frequently seen after market modifications to rebreathers are installing inline shutoff slide valves on the oxygen supply to the solenoid and/or constant flow orifice to enable the ability to isolate the breathing loop from the oxygen supply used to automatically maintain setpoint. The reasoning is this can be very handy for quickly diagnosing and more easily managing specific types of failures of the rebreather. In certain types of unavoidable yo-yo depth profile changes seen in cave diving it also allows the diver to prevent the rebreather from unnecessarily adding oxygen. However, In our opinion these after market modifications are deleting safety in favor of convenience.
Oxygen isolator valves increase the risk that the diver will inadvertently shut off the oxygen supply or forget to open the supply once isolation is no longer desired. Because the slide valve is much easier to close than a normal handwheel operated valve, there is the possibility of something briefly rubbing or brushing against the slide valve, causing it to close. If the diver does not notice the oxygen isolator is closed, hypoxia may occur if the diver is not maintaining ideal loop volume and not properly monitoring their PO2. The risk of hypoxia is even greater if the breathing loop includes an automatic diluent valve (ADV) that remains open while the oxygen isolator is closed. Dive Gear Express does not recommend installing after market oxygen isolator valves on rebreathers.