Diaphragm 1st stages blowing out at depth?

[Eric Sedletzky]

In another thread, there was a video posted about a 1st stage that blew the diaphragm out at 180’.
I’m pretty sure in was the diaphragm because when the guy got back to the boat they turned the air on and air blew out the HP adjustment hex hole and the only thing in there that could blow would be the diaphragm. IIRC the reg was a Zeagle Flat Head.
So, my question is:
How often does this happen, how does this happen, and what could have gone wrong in the reg internally that could expose the diaphragm to full tank pressure that rapidly that a second stage didn’t even have time to freeflow. Or in that case would a second stage freeflow at all if all the air pressure was escaping through a torn diaphragm?
Maybe there’s a knowledgable reg tech out there that could explain how or why this could happen.
This seems kind of freaky to me. I’m starting to wonder just how vulnerable diaphragm regs really are. I had a buddy years ago who did a tech dive in Monterey. He had completed a 200 ft dive and was in deco at 60’ when all of a sudden one of his backgas second stages let loose and freeflowed wildly. This led to a whole chain of events, but long story short he was fine. When they checked the IP later on his Apeks 1st stage it had soared to over 270 psi. It was at 135 before the dive. This of course could have been an HP seat gone bad or a defect?

Are pistons vulnerable to anything like this? Other than possible squeezing out an O-ring or something? I have several pistons and they are my go to regs.
Now I’m starting to look at my Conshelfs with suspicion, or am I being silly?

 

[RainPilot]

If the diaphragm is torn or holes then it will allow gas to flow to the environmental seal. When that gives way, basically the first stage can never reach IP so the tank empties itself through the diaphragms.

I have had a slow leak through a hole in the diaphragm of a reg I bought used, noticed it because the environmental diaphragm got a slow bulge then popped out overnight.

I’ve never had it on any of my 20 or so diaphragm first stages over the last 18 years

 

[scubafanatic]

Hopefully the usual suspects will chime in here. I dive both piston and diaphragm regs and never took that failure mode as a consideration in purchasing or using. I understand pistons are generally considered as a simpler design so maybe that enhances reliability over diaphragm ?

 

[GJC]

As I understand diaphragm first stages, the possible failure modes are:

-The rubber diaphragm could be either old or defective and ruptured.
-The spring retaining cap was either not tightened enough or overtightened (pushing the diaphragm out of position) resulting in a leak around the diaphragm.
-The HP seat failed causing high pressure to rupture the diaphragm. This one is probably unlikely in this scenario as it should have caused a massive second stage free flow if the seat failed.

I would suspect almost all diaphragm failures occur at one of 2 times:

-After a recent service (done inproperly).
-After not being serviced in a very, very long time (I've heard of one that lasted 38 years without servicing before it failed).

Overall, I think both piston and diaphragm regulators are very safe to use. Both have been around since the 1950s or 1960s without major design changes and regulator failures are pretty much the result of improper maintenance and servicing.

 

[reefrat]

Did the person concerned have their reg checked out after the dive to determine the cause?

 

[Eric Sedletzky]

Did the person concerned have their reg checked out after the dive to determine the cause?

That I don't know.
I believe the diver was none other than Dumpster Diver who unfortunately was banned here.
I saw for split second the name “Fife” written on the SMB that he deployed and that is DD’s last name.

If the retaining ring was loose then there would have been a slower progression of bubbles coming out of the diaphragm hole. This was instant and violent.
I was under the impression that the diaphragm on any reg is never subjected to full tank pressure unless there is some other serious problem.

 

[runsongas]

there is also an oring that can fail at the hp seat crown. that can cause the ip to overshoot and pop the diaphragm iirc.

 

[GJC]

That I don't know.
I believe the diver was none other than Dumpster Diver who unfortunately was banned here.
I saw for split second the name “Fife” written on the SMB that he deployed and that is DD’s last name.

If the retaining ring was loose then there would have been a slower progression of bubbles coming out of the diaphragm hole. This was instant and violent.
I was under the impression that the diaphragm on any reg is never subjected to full tank pressure unless there is some other serious problem.

If the diaphragm slips out if position and the seal is lost, a lot of air will be coming out fast.

Full tank pressure would cause second stage free flow and the diaphragm seal should not be affected unless the second stages get blocked or can't keep up with the hp failure point flow rate.

 

[GJC]

U

there is also an oring that can fail at the hp seat crown. that can cause the ip to overshoot and pop the diaphragm iirc.

Unlikely without second stages free flowing first.

 

[GJC]

U

there is also an oring that can fail at the hp seat crown. that can cause the ip to overshoot and pop the diaphragm iirc.

Unlikely without second stages free flowing first. That o ring gap is small and even if the entire o ring extruded, the flow should be less than what would be released from the second stage free flow.