The R4P™

Silica Mines (42.3 kB) Photo: M. Thomas

Surfacing after a 45 minute dive at the Dinas Rock Silica mines in Wales.


The R4P™ is a prototype sidemount rebreather based upon components from earlier projects.

complete & exploded views (35.1 kB)

The small yellow scubber holds about 1.5 kg of soda lime and its duration is limited to less than an hour depending on workload and depth. A 1 kg lead block is attached to the base of the unit for trim. The single counterlung employs a 10 l water bag - this is vastly over capacity, but complete expansion of the lung is prevented by encasing both the scrubber and counterlung in a 125 mm diameter pipe. Gas flow goes from the mouthpiece (from an RGU-FM) to the base of the scrubber, up through the bed and to the counterlung which is fitted with an overpressure valve (Draeger), P-port (for the OxyGuage) and Halcyon unbalanced P-valve (which is used to form a gas tight seal through which O2 and diluent can be injected directly via the dosing unit below).

dosing unit (32.4 kB)

This is the dosing unit to manually add diluent (lower feed) and oxygen (upper feed with and on/off switch, needle valve for a constant background addition of O2 and a manual bypass).

Trials both in a swimming pool and a couple of dives in flooded mines have demonstrated proof of concept. The position of the counterlung (next to the rib cage) affords good breathing properties in all positions - prone and vertical (upright and inverted) - which are necessary for cave diving. The duration of the scrubber is too short for practical purposes and a larger device (the D5) has been built for future use.

Last updated 28 March 2010 by Duncan Priceback