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A modern rebreather, the A.P. Diving Inspiration Vision, popular with technical divers. The corrugated hose leading from the mouthpiece over the diver’s right shoulder is the ‘exhale’ hose of the breathing loop. The corrugated hose leading over the left shoulder to the mouthpiece is the ‘inhale’ hose. The wrist-mounted computer handset is in the foreground. © Bob Anderson

Rear view of a popular closed circuit rebreather (CCR).

The diver’s exhaled breath moves from the mouth through the exhale hose that runs over the right shoulder and into the bottom of the central stack between the two cylinders. From there the exhaled breathing gas passes upwards through a canister holding the ‘scrubber’ sofnalime material, which strips the dangerous carbon dioxide out of the exhaled breathing gas.

After passing through the scrubber, the cleaned, exhaled gas passes into a chamber at the top of the stack, where three or more oxygen sensors analyse the resulting breathing gas to determine how much oxygen the diver has metabolised in the last breathing cycle. Two electronic controllers (essentially minicomputers) then trigger a solenoid (switch) that injects the correct amount of high-pressure oxygen into the breathing mix to raise the depleted oxygen level back up to the desired level (the PO2 ‘setpoint’).