Dive Rite O2ptima Owner's Manual download pdf (Page 10)

O ptima FX Owner’s Manual

Ch. 1 Pg. 5

None of the exhaled gas is reused, so the breathing circuit is said to be “open”, hence the term

“Open-Circuit Scuba”.

The original open-circuit scuba regulator was a two-hose style regulator and was based on

previous designs of closed-circuit Oxygen systems. Inhaled gas comes over the right shoulder

entering the first of two flexible breathing hoses, past a non-return or "one-way" valve and into

the mouthpiece. The exhaled gas travels out the mouthpiece past another non-return valve,

through the other flexible breathing hose and vented to the surrounding water through a final

non-return valve. Eventually this system evolved into a single hose gas supply with a single non-

return located in the mouthpiece. This design change significantly increased regulator

performance. Today even budget regulator systems outperform the best early regulator designs.

Open circuit systems have many limitations, the most notable are:

• Gas selection must be chosen prior to the dive, and with one gas mix per open-

circuit system, additional gases require additional open-circuit systems.

• Gas supply is limited, with low efficiency and poor weight to duration ratios.

• Breathing gas is inspired at ambient temperature reducing the diver’s body

temperature and is dry leading towards dehydration.

However, due to low cost, simplicity and ease of use, the Open-Circuit breathing systems is the

most widespread breathing system in the world.

Semi-closed Circuit Rebreathers

The breathing circuit is similar to the previously described two

hose open-circuit types, except exhaled gas is retained in the

system by means of a counter-lung or breathing bag. The exhaled

gas contains less Oxygen and increase Carbon Dioxide (CO ). The

gas need to pass through a chamber containing a chemical

compound to remove the CO before being inspired once again.

This chamber is commonly called a scrubber, and may be made up

of packed granules or a manufactured cartridge. Since this is a

continual process, oxygen is being slowly depleted along with a

decreasing breathing volume.

Metabolized Oxygen, and lost volume in the most common SCR

design is replaced by means of a flow control valve that

continually bleeds a constant flow of replacement gas (usually

nitrox) into the loop. This valve is set and matched to a specific oxygen concentration, maximum

depth of the dive, and to the oxygen requirements of the user. Most systems require this to be

determined before the dive, however there are designs that allow adjustments on-the-fly. The

second type of SCR dumps a fixed percentage of gas on each exhale and refills the loop from

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Dive Rite O2ptima Owner's Manual Page 10