Diver Dave's Royal Navy CDBA Teardown
The British Royal Navy CDBA (Clearance Divers Breathing Apparatus) is certainly the most highly developed rebreather using the pendulum system of operation. This system uses a single breathing hose, with the scrubber located between the breathing hose and the counterlung. The advantages of this system are several, among them no one-way flapper valves, increased scrubber efficiency due to the granules of scrubber media being presented to the gas on both sides of the grain, and simplicity of design. Disadvantages include the need for the diver to be aware that shallow breathing patterns will result in rebreathing gas that has not fully passed through the scrubber.
The CDBA is quite a complex system that was obviously designed for heavy-duty use by military divers. It relies on a constant mass flow of gas, which can be either a nitrox mixture or pure 02. It contains an integrated weighting system, a bypass valve system, and a bailout gas system in addition to the main cylinders. In order to simplify the presentation of the various sub-systems, I've chosen to break the teardown into smaller areas.
NOTE! This is an EXTREMELY graphics-intensive page. The photographs are all high resolution, and may be downloaded and enlarged for detail study. Be patient, the results will be worth it!
Chassis (vest), counterlung, and weighting system.
Scrubber system and components.
Back-Mounted main cylinders and valving system.
Front-Mounted bailout cylinders.
This rebreather is worthy of serious study, as it uses a system of operation that is unique in it's application to rebreathers other than simple oxygen types. The CDBA was well liked by the divers who used it, and I've received several emails from ex-forces divers who though it was a reliable and comfortable piece of equipment. These rebreathers are not common in civil ownership, as the Royal Navy generally does not offer them as surplus.