DA Aquamaster:
The thing is I have yet to see any actual data to support this claim nor have I seen any design or engineering evidence inside an Apeks or Aqualung first stage that would lead me to conclude that increasing depth would increase the IP beyond what normally occurs in other first stage designs where the IP relative to ambient pressure remains the same as depth increases.
The advertised “overbalanced” first stage is easily accomplished with the newer sealed diaphragm first stages. The only thing required is that the effective area of the outer diaphragm be slightly larger that the internal pressure diaphragm.
The above description only applies when a rigid plunger (pushing device) is used to transmit outside pressure to the inner diaphragm. With the old environmental chamber that were fluid filled, the fluid just transmitted the same pressure as exposed to on the outside of the flexible chamber (ignoring any minor stiffness on the rubber chamber or outer diaphragm).
IMHO the overbalanced was accomplished by accident or because it was too difficult for the engineers/ designers to determine the exact effective area and instead of correcting and precisely matching the effective area of the two diaphragms someone decided to advertise it as an improved feature.
Depending on the diaphragm edge clamping condition and the stiffness of the diaphragm itself, it can be difficult to precisely determine the effective area of a high pressure diaphragm. It may require empirical testing, but if the diaphragm is replaced during service it could affect it slightly.
I totally agree that this whole concept of “overbalanced” is a bad idea being used as an advertising gimmick.
The argument about denser air is so overplayed, IMHO it is ridiculous. To explain this comment it would require a lot more time. Let me just mentioned that density and viscosity are not linearly proportional. Also viscosity affects flow and flow drag, not static pressure.
On a related subject: I have being wanting to set up a submersible IP gauge to check how the IP of several regulators actually track with depth. Since I can’t find a waterproof IP gauge (0 to 300 psi) I may just add holes to a gauge and read differential pressure (to surrounding ambient) rather than gauge pressure (were the reference is 1atm).