Atomic ST1 and Z2..I found this interesting...

[Shabaday]

I have an IP digital gauge that I use inline with the BC hose. I will check my regs periodically. I have an Atomics ST1 and Z2 Octo. I was getting odd readings with it. It would start at 138psi...then go to 136 psi...then it would count down from 136 to around 121 PSI and then go back up again and then count down again...none of my other regs would do that. So I figured at first there must be some major issue wrong with my first stage....so I put my M1 regs after removing all the original items on the ST1 first stage and I had no fluctuation....so then I had to go item by item....once I got to the Z2 octopus then it would exhibit this IP changes. I remove the Z2 and all is well...so I changed the hose on the Z2 and nothing changed...still fluctuating IP...I then take off the face plate and the diaghphram make sure everything is clean and still have the same pattern from the IP gauge....I try a second IP gauge and same thing....so what would cause this in the second stage of the Z2? Regulator has been used 18 times...doesn't appear to leak UW....I tried to upload the video of the IP but says the file doesn't have an allowed extension...it is a .mov....no idea how to change it...tried mp4 as well also not supported

 

[Scared Silly]

You probably do not see it leak underwater because you are breathing from the other second stage. So the IP is not building up so to cause a leak.

The issue is probably the LP seat on the second not sealing. The easy solution is to adjust the orifice. It is easiest to do with an inline tool. But one can remove the second stage from the hose and use a screw driver to adjust it, then put it back on and test.

 

[lexvil]

To add to the previous, it may only be an adjustment, have you tried turning the adjustment knob a turn and seeing if the same thing happens? There is a micro adjuster inside the knob that you can tune if the previous test helps.

 

[Shabaday]

I thought the same thing so I adjusted the knob midway and all the way in and still causing the IP gauge to drop

 

[lexvil]

I thought the same thing so I adjusted the knob midway and all the way in and still causing the IP gauge to drop

Then it’s probably time for a new seat.

 

[Shabaday]

It’s a new regulator. About 8-9 months old

 

[lexvil]

It’s a new regulator. About 8-9 months old

And it has a seat saver but…

 

[Open Ocean Diver]

Try putting the Z2 in a bucket of water and see if you detect any bubbles.

 

[rsingler]

@Open Ocean Diver and @Scared Silly have it right. There's an infinitesmal leak in the octo. There is enough "sticktion" in the first stage that a very slow leak is not enough to trigger first stage valve opening until (in your case) you get a 10+psi difference between IP and tuned setting. Then the valve opens; gas flows up to tuned IP and the valve closes. Then the process starts again.
If retuning, or @lexvil 's suggestion of a new seat doesn't cure it, there's probably a tiny manufacturing flaw in the orifice. Easy diagnosis in the sink, and then examining the orifice under a microscope.

 

[Rusty Shackleford]

I had an issue with a G-250 caused by the wrong size O-Ring on the orifice. The orifice was a bit loose in the air barrel and would slowly unscrew itself and start to leak. This took many dives. A 70-75ish duro viton 010 O-ring on the poly orifice fixed it. Likely swapped the wrong o-ring when I serviced it.

I wonder if similar could be the culprit here?