A closed circuit system means that the breathing gas is continuously recycled in a closed loop. This is in contrast to conventional open circuit diving in which the bulk of the exhaled breath is wasted by venting it out into the surrounding water. With the Evolution/Inspiration Closed Circuit Rebreather, exhaled air is directed into the right hand counterlung then over the shoulder into the bottom of the scrubber unit. It then passes through a Sofnolime filter which absorbs the carbon dioxide before entering a mixing chamber where 3 individual oxygen sensors measure the partial pressure of oxygen (ppO2).

A. Exhaled breath leaves the diver's lungs and is directed into a one-way loop or closed circuit starting at the Inspiration/Evolution's Exhale counterlung.

B. It then travels, via a water-trap, over the right shoulder into the scrubber unit where is passes upwards through a chemical (Sofnolime) filter stack. This effectively scrubs the breathing gas of carbon dioxide.

C. Inside the mixing chamber, three independent oxygen sensors (specifically developed for the inspiration) measures the PO2 of the mix enabling the electronic controller to accurately maintain a constant target level or PO2 setpoint - by injecting pure oxygen when the oxygen pressure drops due to the diver's metabolism or ascent.

D. Scrubbed and refreshed the breathing gas returns via another water-trap on the left shoulder into the inhale counterlung ready for use in the next cycle.

Weighing the same as a 15 litre (95cu ft) air cylinder with regulator and BC, the Inspiration is easy to handle on land and is a dream in the water. The stream-lined casing makes it feel like a 10 litre (80cu ft). Buoyancy control is slightly different to open circuit but soon mastered.

The Inspiration Closed Circuit is a specialist piece of diving equipment. Units will only be sold to divers who have successfully carried out a suitable training course. At present, training TDI, IART, ANDI, RAB and SSI guidelines.