When I first started thinking about building a rebreather, I wanted a Cis-Lunar clone which would do everything for me, automatically controlling my breathing gas so I could dive blissfully unencumbered by worries about PPO₂, END and the rest of those pesky numbers. My early ideas for building an electronically controlled closed circuit rebreather are detailed in my page about an Electronically Controlled Closed Circuit Mixed Gas Rebreather. While the information is generally accurate, my philosophy regarding rebreathers has evolved, leading me to shy away from anything that would automatically control my PPO₂ based solely on an electronic gizmo's interpretation of one, three, or a dozen oxygen sensors. My current philosophy is much closer to that of Gordon Smith of K.I.S.S. fame, who uses electronics to monitor the PPO₂ but physics and brain cells to control it. I also admire the clean design and compact size of Gordon's rig. Here's how I am building my version, guided by the principle of Keep It Simple, Stupid!

Here's a first look at my "KISS Tribute" rebreather:

Back view of the unit. O2 bottle on the right, diluent bottle on the left. Bottles are ~12 cu ft @ 2015 PSI Survivair 5 minute SCBA bottles. Scrubber shell is constructed from 5" Schedule 40 PVC electrical conduit. Mouthpiece is a 1" PVC ball valve drilled axially to accept 3/4" thinwall PVC adapter to SCUBA mouthpiece. Inlet/outlet check valves ~1-3/16" diameter from a dust respirator. No, I didn't copy Dr. Bob's or Patrick Duffy's - I thought I had invented it until I saw their sites. I guess form follows function. I did, however, buy and install a purge valve from Patrick. I expect that anything deeper than oxygen depths will require a somewhat larger bore - a 1 1/4 inch version of the ball valve is sitting on the shelf awaiting conversion.

Front view. Gray tubes are the counterlung shells of 4" thinwall PVC sewer pipe. The white part is a heat-formed piece of PVC which holds the whole thing together and has studs for mounting to a standard backplate. Also visible is the hose running from the oxygen first stage to the "diluent" ADV, since for the immediate future the rig is being operated as an O₂ CCR.

Side views.

Top view. The auto diluent add valve is an AquaLung LPO (Low Profile Octopus) (Thanks Bob Howell!) with the mouthpiece and exhaust ports plugged with epoxy putty (Thanks Tom Rose!) mounted to the top section of the canister. There is no manual add valve (other than the purge on the LPO).

Bottom view, showing the overpressure valve / water trap drain on the bottom of the scrubber canister, as well as the oxygen and diluent first stage regs and the red counterlungs (2 liter Hydromedary Bags, MSR's Camelback-type hydration pack bladders).

Overall dimensions are 20" high, 13.5" wide and 7.75" deep. Weight is 27 lb. empty. Currently the rig is set up in a minimal configuration as an O₂ CCR. Since these photos were shot, I've added a temporary diluent manifold (consisting of a regulator hose coupler and a low pressure tee) to feed the wing and suit inflators and an OC bailout reg.

First Test Dive July 19, 2003

Dive site: Wreck of the F. Morrell off Grand Island, Lake Superior.
 
Depth: 11 feet.

 Water temperature: 52°F

 Configuration: Rebreather mounted to backplate & wings. Short fill (2 liters) of SodaSorb. 12 cu. ft. oxygen, 12 cu. ft. air for wing & suit inflation. Dry suit & dry gloves.

 Bottom time: 45 minutes.

 First impressions: I need more weight! Especially with the light load of lime, the rig was a bit buoyant for the weight belt I was wearing. Work of breathing was a bit disappointing at first until I got used to the slight negative pressure and quit trying to take excessively deep breaths. The auto add valve worked fine; balance was good. The water trap worked fine, easily holding the mouthful of water I accidently blew into the loop. There's no easy way to pressurize the loop (the auto add valve is out of reach) so it's tough to drain any water which may get into the rig. The trap did its job though, keeping the sodalime dry.

 What's next: A big brass diluent manifold to replace the LP tee will clean up the hose routing, as well as moving some weight from my waist to the rig and serving as lifting handle. More dives! (Including a photo dive.) Eventually I'll be adding a KISS-type oxygen metering valve and O2 monitoring.