bouncing inhale on Scubapro D350

[ericpitar]

I have a question on the abnormal breathing on a used SP D350 I recently acquired and did a pool test on.

When I make a *sudden* gasp for air (especialy if I begin the inhale by saying "t"), it feels like the diaphragm, poppet, or something inside "bounces" a few times, thus causing the air delivery to "bounce" as well. (I did the same breathing scenario on my R190 but that did so on demand, sufficiently, and continuously, thus I don't think this D350's performance is normal.)

So, during one big *sudden* inhale, this is what I feel with the D350's air delivery, in more detail:
1) it's hesitant to deliver air at the very beginning
2) catches up on air delivery,
3) gets "short" again, then catches up....
4) short once again, then catches up...

If I were to imagine whats happening inside based on what I could feel, this would be my hypothesis in order:
1) at the very beginning of the inhale, as I make the *sudden* gasp (more noticeable when I say "t" in the beginning), the diaphragm is sucked in (i actually seem to feel it "flip" inwards to push the lever) but is rather slow in moving the lever to open the valve.
2) now that the valve is open, even though I'm just past the beginning and in the middle of my big inhale phase, the diaphragm starts to return to the "rest" position (thereby causing the beginning of valve shutdown), thus prematurely lowering the air delivery
3) before the valve completely shuts, the diaphragm "bounces back in" or is sucked in once again and opens the valve, once again increasing the air
4) repeat steps 2 and 3 above once or twice
5) the rest of the inhale phase feels fine as the air demand is not as large as the beginning and middle.

If I do take a large but gradual breath though, it seems to breathe fine...No "bouncing"....( fyi, I have my MK25 set to 140psi right now.)

In a "field test" for the cracking pressure, the D350 was around 1.3" probably--it starts hissing when the waterline almost reaches that "S" etched at the back of the reg--well after the side exhausts are submerged.

Anyone experienced this or have any feedback?

 

[DA Aquamaster]

My initial thought is that there is a bit too much play in the lever. A tiny bit snugger may resolve the problem. If you shake the second stage and can hear/feel the lever moving, it probably has too much play.

Thought number two is that you may want to try adjusting the venturi on it. The standard position is one click closed from full open. A bit more or less back pressure may eliminate any resonance that is occurring.

Thought number three is a possible lubrication problem with the poppet o-rings causing the poppet to stutter a bit.

 

[ericpitar]

DA....You are awesome! I forgot to mention that when I switch it to Dive mode, there is something moving inside when shook. The sound disappears once it's off Dive mode but I don't specifically remember if I got the same stuttering then. Thanks much for the input!

E