Intermediate Pressure

[Luis H]

Sorry for my confusion if this answer is stated and I am missing it. I know that IP is added to ambient pressure but I thought that the 2nd stage brings the IP down to ambient pressure. So is gas being delivered to the diver's mouth at ambient pressure or IP plus ambient?

Air is delivered to the diver at ambient pressure. The IP is some pressure above ambient (between around 120 to 150 psi above ambient).

The second stage demand valve has a very flexible diaphragm that will open the demand valve when the diver pulls just the slightest suction below ambient. The suction required to deliver air is around 1 inch of water column (1 in WC = 0.036 psi). Therefore the diver will receive air very close to ambient pressure. So close that it is more convenient to measure it in inches of Water column than psi.

 

[АлександрД]

Someday I would like to test an Apeks or an Aqua Lung Legend underwater with my submersible IP gauge set-up. Those regulators claim to be "over-balanced" which is a miss-use of a technical term. They are actually over-depth compensated (or something like that).

In other words, they have a dry ambient chamber with diaphragms (inside and out) with different "effective area" and a solid a solid pressure transmitting rod between them. The difference in the diaphragm "effective areas" created slight IP increase as a function of depth.

This has been discussed a lot in the past, but I haven't had a chance to actually measure one.

You can buy sealed IP mini gauge Mini Gauge
Once I try it - it works! it increase IP with depth!
Yes, it has one problem - it shows "near-absolute" pressure, and increase with the depth.

...there is SEALED LP Gauge: Mini Scuba Gauge, PG-JH2-LP - AROPEC SPORTS CORP.

it has 3/8 thread, as normal hose. Just screw it in reg and use underwater
I used it - it works

And small add-on for "Overbalanced" regulators:
At this moment only one scheme is realized - with two membranes - main, and sealed dry chamber membrane (only with plunger between. with liquid, like Pioneer or Mares - it will not work too). Without dry chamber, or using simple single-piston scheme - no way to make overbalanced reg.
But it also require (for better reliability) using balanced 2nd stages. On the deeeeepth standard non balanced 2nd stage can start freeflow.

 

[buddhasummer]

I did some playing with an Apeks FSR and a tuned as lightly as I could (1.2") conshelf and it started to leak at an increase of around 11psi. So I figured I would be good using the FSR/conshelf combo to depths of around 50m. Having said that I ended up unsealing the FSR for the sake of simplicity.

Any excuse to post this photo, it looks so pretty.

I never took the sealed FSR/Conshelfs to 50m but did to around 42m and it was fine.