Quote: (Originally Posted by solocavediver)
OK folks so let's express this mathematically (excuse me I'm a mathmo). What I call an "unbalanced" regulator and Joe calls an "uncompensated" regulator produces a roughly constant second stage pressure of 14 bar. So, below 130m nothing will flow out of it - not usually a problem with the recreational divers who buy this kind of reg, since they stop somewhere around 40m. <snip>.
As far as I am aware, you can't buy (what I call) a
non-depth compensating first stage - this functionality is achieved by doing a home made modification to the first stage to fix the IP and prevent it increasing (absolutely) with depth.
All first stages that you pick up off the shelf AFAIK are designed such that the surrounding water pressure changes the (absolute) pressure passed through the reg such that there will always be a considerable pressure above ambient. Whether the gubbins inside is a piston, a diaphragm, sealed, exposed the concept is the same. I agree that different reg designs have slightly different characteristics regarding the linearity of the pressure increase over ambient that they generate, but the result in a normal OC world is the same (ignoring things like flow, density and sonic limitations) - gas comes out at pretty much any depth.
You don't want this in an MCCR, unless you have a depth compensating orifice to maintain a constant molecular flow of oxygen into the loop. IMO it's easier to fix the IP to not compensate with depth, then fix the size of the orifice and accept that there is a limitation on it's use...