Scuba Diving on a Closed Circuit Rebreather - How it Works

In this article we are going to discuss the workingsHowever, with a CCR it has the correct amount of
of the Closed Circuit Rebreather (CCR), with a focusloop volume and the integrated BCD set to suit the
on the APD (or Ambient Pressure Diving Limited)current depth. Then, it will not matter how fast or
Evolution and Inspiration models.slow the diver breaths he/she will stay still - Cool:-)
Who makes the APD Inspiration / EvolutionDiving on a Rebreather. CCR's work on fixed Set
Rebreather? Ambient Pressure Diving is based inPoints or Partial Pressures of Oxygen (PPO2). The
Helston in Cornwall, England and owned by Martintwo standard Set Points on the APD units is 0.70 and
Parker. The whole production, assembly and testing1.30 however they can be fully adjusted above or
of their Closed Circuit Rebreathers is conducted all inbelow the surface. A Set Point of 0.70 means that at
one factory. No actual figures are produced regardingthe surface (Sea Level) the diver would be breathing
production numbers but I would estimate in thethe equivalent of 70% Oxygen. If the dive was at 10
realms of 90 to 150 units per month are produced.metres he would be breathing 35% Oxygen because
So, how does a Closed Circuit Rebreather work? Theat 10 metres there are 2 Atmosphere (ATA) of
CCR has several key elements. The diver puts thepressure (0.70 / 2 = 0.35). So at 60 metres there is 7
mouth piece of the breathing loop into his/her mouth.ATA the diver would be breathing 10% Oxygen -
The diver breaths out and the expelled air leaves thenot good, this will not support life but you get the
breathing loop and enters the exhale counter lungidea.
which is located on the right shoulder. Any moistureThis is why we have two Set Points. On a typical 40
or water droplets are removed by a baffle platemetres dive the Diver travels down to 40 metres on
fitted into the entrance of the exhale counter lung.a 0.70 Set Point. Change to 1.30 at depth and
The air now passes from the exhale counter lung tocontinue all the way to his/her Safety Stop at 6
the base of the scrubber unit which is contained inmetres. Then they would change back to 0.70 prior
the back mounted case. As is passes through theto leaving the Safety Stop. However, this all changes
scrubber the CO2 (Carbon Dioxide) is removedwhen doing decompression diving.
converted into heat and moisture. The cleaned airNormally, for dives to a maximum depth of say 45
passes in front of three oxygen cells. These cellsmetres they would have two cylinders fitted into
measure the level of oxygen in the gas comparedtheir rebreather. One of pure 100% Medical Grade
with the amount of oxygen that should be thereOxygen and one of Air or 21% Oxygen. This cylinder
according to the integrated computer - More aboutis referred to as the Diluent, so this set-up would be
this later. An oxygen solenoid adds a precise amountan Air Diluent CCR. For deeper dives the Air Diluent
of oxygen according to the computers requirementswould swapped out for different mixtures of Trimix
and the gas passes to the inhale counter lung,(Helium, Nitrogen and Oxygen). Cylinders for the APD
mounted on the left shoulder. The diver breaths inEvolution and Inspiration are either 2 or 3 Litre in
and draws fresh air from the inhale counter lung viacapacity filled to 200 Bar.
the mouth piece and breathing loop.Longer dives on a CCR - Depending upon depths and
The idea is to have either one lung full in you or onethe particular user the units are capable of diving to
lung full in the unit, never both. This is called loop150 metres (correct training required) for durations of
volume management.2 to 6 hours.
Managing buoyancy when diving on a Closed CircuitThese are amazing pieces of equipment and great to
Rebreather - With conventional scuba you breath inuse for scuba diving.
and go upwards, breath out and go downwards.