The Pelagian Diver Controlled Closed Circuit Rebreather is exactly what the name suggest - diver controlled. This means that oxygen is added mechanically through a fine metering needle valve at a constant flow set slightly lower than the divers metabolic rate. As the PO2 slowly drops the diver add oxygen manually with a push button. Another similar approach used in other rebreathers is to use a non adjustable orifice instead of the needle valve. The disadvantage with this system is that the regulators 1st stage need to be isolated from the water pressure in order to keep the flow constant, which means that when the water pressure exceed the set intermediate pressure of the 1st stage regulator - the flow stops. As the Pelagian DCCCR is equipped with a needle valve the 1st stage is kept responsive to the water pressure and will raise the mass flow of oxygen during deeper decents. The diver can balance this by turning down the needle valve while confirming the PO2 with the O2 displays. This means you can dive deeper than with an orifice fed rebreather. How deep? Theoretically very deep. The practical limitation is the amount of bail out gas you can carry or stage and the scrubber life.
[ Working principle ] [ Sensor validation ]
[ Trim and balance ] [ Frame work ]