info request

I am new to the discussion group thing, so I'm not sure exactly how to proceed. So here goes. My name is Tim Garton, I live in Ketchikan, Alaska. I am in the design phase for an ambient pressure submersible. I have most of the details worked out, and I have made a small model to test weight positioning, buoyancy chamber placement, etc. I found this PSUB thing and I thought: man this is weird! There are actually other people out there who are as crazy as me! My neighbors think I'm nuts, and everybody wants to take out life insurance on me! Nice friends huh? Well, I'm hoping that there is somebody on this discussion system who has an ambient sub, most of the emails I've seen so far have dealt with 1 ATM machines. I haven't had a chance to experiment with an idea I had to use a regular SCUBA reg with a float valve to keep the air in the main chamber at a constant level (mostly because I dont have the main chamber yet), so I'm hoping to see if anybody would want to tell me what they did to overcome this. I tried to figure out a formula using a CFM figure, but I'm not sure it would be fast enough. The air would need to be added on descent as the water level rises in the main chamber. To compensate for air expansion on ascent, I have devised an exhaust system that would have the air escape at the desired level. Any information on these things would be appreciated.