Modified C96 for cave use

Whilst I like diving the inspiration and using O/C bail out. I wanted a second rebreather I could use both within UK caves on it's own and as CC bail out. I have modified a C96 Oxygen rebreather for this purpose. It has taken me through the end of the choke in Cheddar (beyond a -55m elbow), from Keld head to Kingsdale Master Cave (an 1800m through trip) and on dives of over 2 hours in france. Its not perfect, but it works.

The credit for this design goes to a number of people, who I have shamelessly stolen ideas from. This rebreather is not home built, there are no home made parts in sight. It is assembled from proven working components. In no particular order thanks to

This is the front View, The original O2 cylinder has been replaced with a DIN version, I have a dumpy 3L cylinder for resurgence use and lighter 2L for cave carries. The C96 has 4 reinforced areas on the sides for cutting holes in .The original O2 inlet has been moved from the middle of the right hand side to the bottom right hand side. The fitting is 3/8 UNF, which makes connecting gas feeds easy. Gordon Smith supplies fittings to convert from 3/8 UNF to swagelok. I have added an inspiration dump valve on the lower right hand side, an inspiration inflator on the center left hand side and 2 Draeger "P" connectors on the center right and at the top. The side "P" Connector is used for the oxygauge, the top "P" connector is used for either an ADV unit, see below, or a second ppO2 monitor (VR3) I have added the KISS O2 injector to provide some level of "automatic" O2 addition.
This is a standard KISS Oxygen addition system, with a swagelok tap added. When the unit is used in "Bail out" mode this tap is turned off, this keeps the injector pressurised and water free, without continuous oxygen injection. The KISS System is at present depth limited to about 70m, I am intending to change the restrictor to increase the depth capability of the unit.
The Top of the rebreather is shown here. You can see the ADV unit. This is a modified version of Bob Howell's Inspiration ADV. It has a "P" connector on the bottom to fit into the bag and a dump valve on the top. With the dump valve fully open, this will keep the bag empty, but at ambient pressure. For "intentional use" or carrying the unit underground, the ADV unit can be removed and replaced with a second O2 monitor. Diluent is then added using the manual injector on the Left hand side. All fittings are inspiration compatible.
As shown, The ADV is completely removable, note the inspiration fitting on the end of the hoze. These fittings are not suitable for O/C use as they are designed to restrict the flow of gas severely, however for a descending rebreather diver needing a "loop top up" they work fine.
The unit can be worn on a standard Dragon cave diving harness with sidemounts, or mounted over inspiration counterlungs. Note the hoze from the ADV running round the right hand side of the unit, to be connected to a female inspiration hoze on my side mounts.

Even without monitoring, this unit would easily allow a 12 Litre cylinder to be extended 3:1 in semi closed mode, with the ADV fitted, this could be accomplished whilst scootering or performing other tasks.

to see how the unit mounts on an inspiration click here. It's big, but it will take me a _long_ way into a cave without the need to stage bail out O/C. I'd also argue that it's smaller than a DIR Diver with 6 stages and a set of doubles :-)) and of course, the inspiration can be removed and the smaller CCR used on it's own further into the cave if needbe.

John Volanthen john@hns.net