Scuba,Diving,Closed,Circuit,Re sports Scuba Diving on a Closed Circuit Rebreather - How Does A Reb
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Rebreathers are a great wayof enjoying longer dives (we had rebreather divers on our boat last week inKota Kinabalu, Sabah who enjoyed a four hour dive!) and getting closer tomarine life as there are no noisy bubbles to scare fish away. Imagine diving insilence except for the crackling from corals.Rebreathers are a greatoption for experienced recreational divers looking to take their divingfurther. One of the first questions we often get asked by our diving customerswhen they see a rebreather on our boat is How does it work?. The rest of thisblog provides a simple overview of the workings of the Closed CircuitRebreather (CCR), with a focus on the APD (or Ambient Pressure Diving Limited)Evolution and Inspiration models. It gets a little technical (as a closedcircuit rebreather is more technical than diving on open circuit) but onceyouve learned how to dive on a rebreather youll have the knowledge to prepareand dive safely on a rebreather and enjoy many long divesSo, how does a ClosedCircuit Rebreather work?The CCR has several keyelements. The diver puts the mouth piece of the breathing loop into his/hermouth. The diver breaths out and the expelled air leaves the breathing loop andenters the exhale counter lung which is located on the right shoulder. Anymoisture or water droplets are removed by a baffle plate fitted into theentrance of the exhale counter lung. The air now passes from the exhale counterlung to the base of the scrubber unit which is contained in the back mountedcase. As is passes through the scrubber the CO2 (Carbon Dioxide) is removed /converted into heat and moisture. The cleaned air passes in front of threeoxygen cells. These cells measure the level of oxygen in the gas compared withthe amount of oxygen that should be there according to the integrated computer(see below). An oxygen solenoid adds a precise amount of oxygen according tothe computers requirements and the gas passes to the inhale counter lung,mounted on the left shoulder. The diver breaths in and draws fresh air from theinhale counter lung via the mouth piece and breathing loop. The idea is to haveeither one lung full in you or one lung full in the unit, never both. This iscalled loop volume management.Diving on a RebreatherManaging buoyancy when diving on a Closed Circuit Rebreather With conventional scuba you breath in and go upwards, breath out andgo downwards. However, with a CCR it has the correct amount of loop volume andthe integrated BCD set to suit the current depth. Then, it will not matter howfast or slow the diver breaths he/she will stay still Cool:-)Diving on a Rebreather.CCRs work on fixed Set Points or Partial Pressures of Oxygen (PPO2). The twostandard Set Points on the APD units is 0.70 and 1.30 however they can be fullyadjusted above or below the surface. A Set Point of 0.70 means that at the surface(Sea Level) the diver would be breathing the equivalent of 70% Oxygen. If thedive was at 10 metres he would be breathing 35% Oxygen because at 10 metresthere are 2 Atmosphere (ATA) of pressure (0.70 / 2 = 0.35). So at 60 metresthere is 7 ATA the diver would be breathing 10% Oxygen not good, this willnot support life but you get the idea.This is why we have two SetPoints. On a typical 40 metres dive the Diver travels down to 40 metres on a0.70 Set Point. Change to 1.30 at depth and continue all the way to his/herSafety Stop at 6 metres. Then they would change back to 0.70 prior to leavingthe Safety Stop. However, this all changes when doing decompression diving.Normally, for dives to amaximum depth of say 45 metres they would have two cylinders fitted into theirrebreather. One of pure 100% Medical Grade Oxygen and one of Air or 21% Oxygen.This cylinder is referred to as the Diluent, so this set-up would be an AirDiluent CCR. For deeper dives the Air Diluent would swapped out for different mixturesof Trimix (Helium, Nitrogen and Oxygen). Cylinders for the APD Evolution andInspiration are either 2 or 3 Litre in capacity filled to 200 Bar.Longer dives on a CCR Depending upon depths and the particular user the units are capable of diving to150 metres (correct training required) for durations of 2 to 6 hours.These are amazing pieces ofequipment and great to use for scuba diving.Find out more about learning to dive on a Rebreather in the tropical waters of Sabah, Borneo.
Scuba,Diving,Closed,Circuit,Re