Tank Valve Issue - Out of Air Incident

[pxguru]

Hi,

Just wanted to relate an issue I had last week and which I don't yet fully understand.

I was on my 14th dive of a 6 day trip to Siapdan, Borneo (Sabah -East Malaysia). It was a routine 22metre dive to do some macro photography. The weather was wonderfully clam and the water a toasty 29 deg C

Approx halfway through my dive (30 mins), I suddenly experienced an out of air stuation. One breath through my Zeagle reg was fine, the next - nothing..the horrible realisation that sucking on the reg gives nothing...I quickly checked my Suunto D9 (which hass a wireless tank pressure transmitter) and my analog pressure gauge. The transmitter said zero air, the gauge said 100 bar. I swam over to my buddy and calmly suggested my tank valave may not be open fully ( i had a quick suspicion that the boatman who ahd changed over the gear from dive 1 to dive 2 may not have fully opened the valve when I asked him to do it - the wireless D9 transmitter needs to pair with the dive computer when gearing up so the tank valve remains closed until I put on my BC and I open the air), but he failed to register this suggestion, so I indicated out of air. The buddy breathing was fine and we found the DM who fiddle dwith the tank valve and hey presto, air back into my reg.

The rest of the dive proceeded fine.

On the surface the DM noted the tank valve was fully open (ie it hadnt been backed of 1/4 or 1/2 turn as I would normally do. He muttered something about a venturi vale sticking as the air pressure in the tank dropped. Frankly I didnt understand what he was on about and told him to get the tank valve checked out anyway.

So a few comments and questions: (note I qualified in 1992, have 400+ dives and am advanced level - have dived US, Caribbean, and all over Malaysia, Thailand, Indonesia, Phillipines)

1. I should have immediately signalled out of air and tried to solve the problem while I was breathing! I didnt panic and was more puzzled than anything - too much thinking !!

2. I should have opened and checked my own air valve on the tank

3. having checked my computer download log from the D9 I have confirmation of zero air pressure for approx 90 seconds. I assume the analog gauge remained pressured up fromthe residual air in the hose, giving a potentially misleading reading (even though I knew there must be half a tank of air in the cylinder)

4. Does anyone know the workings of a cylinder valve - if it was "over opened" would it have caused this problem. If not, any other suggestions as to what could have happened ?

Cheers,
Steve

 

[t-mac]

Wow. This is truly bizarre. I agree 100% with your analysis (esp alway check your own air!). I do not believe that "over" opening a tank can have an adverse effect like this. The quarter-turn back is more to avoid potentially damaging the valve, which is made of soft brass, but I do not think that would allow it to close itself back off and cut off your air. The venturi explanation definitely doesn't sit right either. That can effect how hard/easy the reg breaths, but not cut the air off altogether. My suspicion is some crap in the tank (rust or other debris) that stopped things up. Manipulating the valve freed it back up. Even that is hard to imagine, though. Were you at any time head-down such that debris could have come from the bottom of the tank into the valve? Glad you made it through and congratulations on your composure in handling this! I hope I could do the same if put in the same situation.

 

[Wookie]

It is possible, although I've never heard of it happening, that the teflon insert of the valve came apart from the brass seat and plugged up the works. I have had the teflon inserts come apart, but it typically allows the tank to not close tightly, not to cut off air flow, bui I wouldn't put anything past anything to screw up. Out of curiosity, did the crew disassemble the valve while you could see it? Did the cylinder remain in service with no other problems?

I think your reaction was splendid. No panic, no drama. Head to your buddy and get the problem fixed, and continue the dive. I might have aborted, as an unknown problem that fixes itself is merely a warning to go affect a real solution, but kudos to you anyway.

 

[ianr33]

Does the computer readout show a very rapid drop of pressure?

I'm going with the crud in the diptube theory.

I always turn my valves full on. (No 1/4 turn back)
That way they are either ON or OFF. Both of which are immediately obvious. No possibility of being OFF but turned ON a 1/4 turn. That can cause a reg to breathe OK on the surface but not at depth. (happened to a buddy of mine)

 

[eelpout]

1. I should have immediately signalled out of air and tried to solve the problem while I was breathing! I didnt panic and was more puzzled than anything - too much thinking !! If you were calm enough to try to figure out what was wrong I see no reason to give your buddy the out of air signal till you need his/her air. It seems you had a preety good ascent with no issues.

2. I should have opened and checked my own air valve on the tank. I always turn my air on, and jsut to make sure if itis on a 100% breathe off your 2nd stage and look at your SPG and see if the needle moves. That is usually a dead giveaway if your valve isn;t turned on all the way.

3. having checked my computer download log from the D9 I have confirmation of zero air pressure for approx 90 seconds. I assume the analog gauge remained pressured up fromthe residual air in the hose, giving a potentially misleading reading (even though I knew there must be half a tank of air in the cylinder) That is sorta strange because the air in the line would have been consumed as you were running low on air.

4. Does anyone know the workings of a cylinder valve - if it was "over opened" would it have caused this problem. If not, any other suggestions as to what could have happened ? As mentioned above, mechanically even if that seat broke apart, it will usually cause the valve to leak when it is turned off.
You never know what you get when you dive with rental tanks. I tried to rebuild our rental tank valves as soon as they feel different when you turn them on/off. After filling tanks for 32 years you get the the feeling doww pat. Kudos to your response to the out of air situation. I will admit that I have in the past jumped into the water without my air turned on. It is embarrassing and darn right stupid. I will admit at one given time I was a stupid diver : )

 

[TSandM]

What baffles me about this story is the inconsistency between what the SPG was showing, and what the transmitter was indicating. Transmitters fail, but that doesn't cause a problem with air to the regulator. But if there is, for example, a dip tube blockage, as you attempt to remove air from the system, pressure will fall to ALL ports. I can't think of a situation where the two high pressure ports would be seeing a different pressure, unless something blocked the orifice to one of them, which means a major problem inside the first stage.

I'm assuming this was your regulator, since you had a transmitter on it. Have you taken the first stage in for service?

 

[ianr33]

If the hose going to the spg had a smaller pinhole in it than the hole in the transmitter it MIGHT hold pressure longer. The hose will also be holding more gas so would hold pressure longer.


Agree it's odd.

 

[Couv]

Welcome to Scuba Board and congratulations on keeping your head.

You were probably diving with a near closed valve. I.e. not turned on all the way.

Because of the small orifice in the HP hose and given hose length, it acts as an accumulator. That's why you can turn your air off-purge, but when you remove the regulator from the tank, you still get that psst. I don't think the gage is suspect because a 100 bar (if my math is close is ~ 1450 psi) error would surely be noticed.

I do have a question though. Once you suspected your valve was not all the way on, why didn't you reach back and ensure that it was open?

Couv

 

[dumpsterDiver]

I suspect that the valve was barely opened. The DM cranked it open for you and then lied about it to sheild his co-workers from any liability. I know that is what i would have done, but i might have blamed it on a flux converter, rather than a venturi.

 

[Hetland]

Were you close to an up/down/travel line? I'm thinking rolloff.

I (now) always dive with my valve 100% open. If a divemaster dials it back, I open it up again. It is your responsibility to ensure that your valve is turned on, and that you have a sufficient gas supply for your planned dive. There is no excuse for diving a valve that isn't 100% open. I know many folks teach the 1/4 rollback, but what are your real-life choices here? The very distant possibility that a valve might be damaged one day, or the very real possibility that a half-opened valve will cause you to take a breath that isn't there?

Part of my pre-dive is looking at my gauge/computer as I breathe on the surface. I watch for the change in pressure before I hit the water. If I'm doing a shore entry I do a second check to ensure the exhaust valve is working properly.