The TP2000 is a two-fold experiment. One of the big hassles with using rebreathers in technical diving is the need to carry huge amounts of open-circuit bailout gas, which can make life really complicated. Sometimes, for really deep and long dives, the logistics of bailout gas management end up becoming the limiting factor of the dive. Now, that doesn't make a whole lot of sense, because you've got this machine on your back that will allow you to breathe for 8 hours at 300ft on 20 cubic feet of gas, but if you're, say, in a cave, you've got to carry or stage enough Open Circuit gas to get you back out from the furthest point of penetration.
So, naturally, the answer to this is to carry another rebreather, which solves all of those problems cleanly.
The other design goal of the TP2000 was that I wanted to see how minimalist an effective rebreather could get. I put the whole thing together one evening over a period of a few beers, er, hours. ;)
I used the TP2000 on a few dives, and I liked the basic design very much, so it was quickly replaced by the TP3000, which has a bunch of improvements like triple O2 sensors, automatic diluent addition, and electronic setpoint controls. When I get some time, I'll snap some pictures of the '3000.
That new functionality isn't strictly minimalist for bailout use, but in addition to use as a bailout RB, I'm not taking my "real" rebreather on recreational dive trips anymore - the "big rig" now gets reserved for technical dives.
At 19 pounds fully loaded and charged, the TP is a dream to pack, carry, and dive. Plus pre-dive checks take about two minutes (vs. 20-25 on my "big rig"), and a full end-of-day cleaning and recharging takes about five minutes, vs. 20 minutes.
Work of breathing is surprisingly good, at least as good as any other rebreather I've dived, which makes sense, when you consider that there's nothing to offer resistance besides the scrubber cannister.
How much did it cost to build? For me, not a stinkin' dime, because I had all the parts laying around. But I totalled up what it would cost if I went out to buy all the parts, and I was pretty surprised that it ended up being around $600-$700, although most of that cost is in the tanks, regulators, and mouthpiece.
-Will Smithers, Mar 1999