Unknown Problem

[Jeff Buetemeister]

During a recent Live-Aboard trip to Palau we were doing our final dive of the week at Chandelier Caves - normal a fairly shallow 15-20 minute dive. During the dive there are 4 chambers we surface in where we can take our regs out and take several pictures.

At the start of the dive I had 3040 psi (80 ct ft tank) as I did my initial decent, as usual I watched my computer (air integrated) to monitor decent rate and as a triple check to ensure air was on. Everything went fine during the dive, we entered each of the chambers. After decending out of the 4th air pocket I swam along the bottom toward the opening to get a good picture of the light streaming in with the divers. --- This is where the problem was noticed...
My reg began breath hard so I immediately checked my air (didn't after initial decent due to the short/shallow dive) --- 160 psi! so I signaled a nearby diver who came to my aid, a few breaths after he approached - no air - so I followed training, secured his alternate and we swam out - did a safety stop and surfaced. I immediately checked my tank valve which was open, then check my pressure which was now showing 2800 psi! once I re-boarded the boat I tried to recreate the problem to no avail.

When I returned home I printed out my dive profile and when I started the dive it showed 3040 psi with a linear decrease to zero psi at 14 minutes where it stayed until I was out of the water. There were to pressure rises in the graph when I was in the air pockets breathing cave air or while I was breathing my buddies alt.
I took this info to my dive shop and we took apart the reg's 1st stage which was in perfect condition. I contacted the manuafacture, several VERY experienced divers and they had nothing. Since then I have nervously dove with the reg about 10 times with no problems.

Data:

Water Temp 84 degrees
23 prior dives that week with same tank (32% EANX)
1st Stage: Dive Rite R2500 (about 160 dives on it - serviced at 90)
Depth - Max: 54 feet (that was near the end - most of the dive was 20 feet)
Time: 14 minutes to no air
Starting psi 3040
Ending psi 2800 not counting the problem
No prior problems

At this point I'm probably going to but a new 1st stage...

Any Ideas???

Thanks!

 

[james croft]

May be possible that you did not have your air turned on fully at the tank. At depth it was not delivering enough air but worked OK at surface.

 

[Jeff Buetemeister]

That was the first thing I thought too bit I checked it when I surfaced and it was open. Also, while in the air pockets and during the swim out using my buddy's alt I would have expected to see an increase in pressure by my comp didn't record any increases...

Thanks

 

[Cacia]

Crud stuck in the reg when you inverted?

Usually people suck some sludge when that happens though.

I almost always try and invert a rental tank at a shallow depth before inverting in an overhead....or going deep. Generally you only invert the tank like that when crawling "into' something.

 

[Jeff Buetemeister]

We checked that too, the screens in my 1st stage inlet were clean and I had used this tank for 23 back roll entries during the week... unless something "broke" loose inside the tank?

An interesting thought is that this entire issue could be explained (mostly) if I had used maybe a 6 cubic foot tank instead of an 80...

 

[Otter]

What if the crud was big enough to partially or completely obstruct the dip tube in the tank (assuming there was one) and hadn't made it to the first stage? You sure you used the SAME tank each time? As you stated, its possible that it just chose that time for something to come loose.

 

[japan-diver]

The symptoms sound like the tank valve was not fully open so shut the air off at 2800 or so - explaining the remainder of the air in the tank. If it was not the valve turned off partily it may be a problem with the valve. If you have had the regs checked by a good shop and they can find nothing wrong - being that you have dove 10 times more with them- I doubt it was a reg problem. There is not much in a first stage that would duplicate the symptoms you describe. This was a valve problem either not turned all the way on (which is what I expect) or something else broken on the valve.

 

[Cacia]

I would not want to be in Chandelier Cave sharing air, tight quarters, ugh. That must have been enough to make you a little paranoid. I've had the partially open valve cut me off at 70 ft solo and it shook me up for awhile. *Helpers* can twist your valve as you step off and you never even know. I wonder if doing a viz on the tank would show anything.

 

[Jeff Buetemeister]

I'm 99.9% certain it was the same tank. During the week all we do is disconnect the first stage after a dive then between dives they refill the tank and before we dive we check our EANX and reconnect the 1st stage.

I do agree that the only possible explanation is a valve that was partially closed... I know I opened it per my usually ritual but between my buddy checking it and the boat crew checking right before we roll I someone may have gone the wrong way...

Yeah - it was a bit unsettling, especially since it was high tide so, had i not found my buddy, I doubt I would have found the air chambers around all the stalactites...

The really odd thing is, the night before a group of us were talking about redundant air sources... hmmm... suddenly the conversation takes on all new meaning

Thanks for everyone's insight!

 

[redacted]

If I'm understanding this correctly, the regulator never failed to deliver gas, so it may not be a regulator problem at all. The tank valve is a prime suspect but you checked it. And the monotonic drop in pressure even when the tank was not being breathed just doesn't go with that cause. It might be time to take a hard look at your computer as a suspect.