Basic SCUBA (Air Supply) Equipment Faliure: How frequent does it happen?

[Diver0001]

I'm nowhere near as experienced as many of the posters that have already given their lists. I have seen or experienced a few events, though and found that most of the time they are trivially easy to deal with in a Rec environment.

I have had the following:
1) Overflow/dump valve fail on BCD (I had modified an old horse collar and this was my second dive with it.) No big deal, dive with very little or no air in my BCD anyway. Took it home and repaired the valve.
2) Minor freeflows due to cold water. Not full on freeze-ups but some 5 second freeflows here and there. (I've witnessed these, not had them happen to me personally.)
3) O-ring blown on a tank valve at the surface. No big deal, back on the boat, swap tanks and get wet.
4) A couple of minor second stage leaks and a minor first stage leak. Dribbling bubbles isn't a big deal, in my opinion. Watch the pressure gauge and repair during SI.

I keep my dive profiles conservative (as if I had a choice--still an air hog) and know how to service/repair my own gear. That, pre-dive inspections, and keeping a calm demeanor makes all of these equipment malfunctions non-issues.

You don't have to have massive amounts of experience to have a major failure. I've seen students in the pool who weren't even certified who had problems that would have scared the bejezus out of a lot of experienced divers.

The chances that something spectacular will happen obviously increases the more you dive, but it remains a lottery.

R..

 

[boulderjohn]

Since there has been so much talk in the past few posts related to water in the tank and dip tubes, and since I'd be willing to be that a large percentage of divers have never seen the inside of a tank, I thought a little general information might be helpful.

The valve at the top of a tank screws into the threads in the neck of the tank. They are not in there super tight--you can sometimes unscrew it by hand, although even then it isn't easy. At the bottom of the valve is a simple opening that allows the air to enter the valve. Because there is a possibility that air or corrosion could clog that opening when the tank is inverted, a very small pipe called a dip tube, only a few inches long, is inserted into the hole and screwed tight. This means that when the diver is in a head down position, the air enters the hole in the pipe several inches above the neck of the pipe, making it unlikely that anything will clog it.

In my experience, those dip tubes can come unscrewed and fall out if they are not in there really tight. If they do, the only problem should be an annoying noise as it slides around in the tank when it is moved. There should not be any water, rust, or debris in a well-maintained tank, so there should never be any other problem. I know one very well known diver who never puts a dip tube in his tanks because he figures there is no need for it, and it is annoying when they come out.

On the other hand, if the tank is not well-maintained, or if it is filled by a shop using sloppy technique, water, rust, and debris can get in. In that case, you certainly want a dip tube in there, and even that might not be enough in extreme cases. I was once asked to do a visual inspection of a steel tank only a few months after it had gotten its hydrostatic test done. The tank had not been used in that time. When I opened it up, the walls of the tank were lined with loose, powdery rust, the obvious result of improper drying after the hydrostatic test had filled it with water. If the diver had attempted to dive with it, I have no doubt it would have been clogged pretty quickly, even with a dip tube.

Contrary to what many shops will tell you, going out of air on a dive will not in itself put water in the tank. You have to do more than that.

 

[Diver0001]

Contrary to what many shops will tell you, going out of air on a dive will not in itself put water in the tank. You have to do more than that.

Thanks for that good post, John.

I'll just add this. While going out of air may not always be enough to allow water in the tank, it *is* a prerequisite. The easiest and best way to keep the tanks rust and water free is to ensure that you always end the dive with some air in the tank. Moreover, if you *do* go OOA then it is wise to get the tank visually inspected before the next dive.

R..

 

[GrumpyOldGuy]

I had a dip tube clog leaving approximately 1700 psi unusable in the tank.

I had a regulator freeze shut.

I had a regulator first stage freeflow that emptied the tank.

I had an inflator o-ring extrude.

Redundant air is good.



Sent from my SPH-L710 using Tapatalk 2

You were being a bit selective on your quoting. I also said

I have had gear fail, but the normal checks your trained to do before you splash and basic maintenance takes care of 99% of the issues. Freeze flow (1st stage) and extruded o-rings do happen, my time has just never come.

I never said don't get a redundant air supply, I have 3 pony bottles. I just pointed out most of the issues can be addressed with proper gear checks and maintenance.

 

[iluvtheocean]

During a weight belt check in Cozumel 2006 from 6m deep, the inhalation/cracking adjustment knob assembly on my 2nd stage primary long hose reg catastrophically blew-out (reg was an old Oceanic Delta II): and my buddy was nowhere in sight. . .

The skill to perform in such a contingency is called feathering/modulating your tank valve to take a breath as needed --and then shut the valve back down-- as you perform a CESA from depth, while breathing from your back-up reg/octopus (i.e. don't bother attempting to "sip" off the free-flowing malfunctioning reg). Takes some practice to do it properly on a single tank: right hand reaching back to feather the cylinder valve, while the left hand operates the BCD/Wing inflator hose dump valve to control the ascent.

In a non-fixable free-flow scenario, whether diving singles or doubles; in a team or solo; overhead or open water: Do not let precious breathing gas totally expire if you can manage to control it. . .

Also on remember on that reg adjustment knob: righty tighty & leftie loosie !​

this sounds like a sound scenario to do an OW ascent / CESA while loosing as little gas as possible. depending on your depth/NDL, etc you might still be able to do a safety stop depending on if solo or buddy diving -

 

[Adventure-Ocean]

I dove 1000's of dives over 40 years and had only minor problems. The worst I experienced was a free flowing regulator a few times and I had my main regulator line burst. Clearly my fault from lack of maintanance. I started in the 70's so the regulators have improved greatly. The first few years I dove without a BC or vest. Wearing a shorty and using a steel 72, all balanced pretty well. I memorized the tables because we didn't use computers.

If you dive a lot it's easy to slack on looking over your gear. A good maintanance procedure will ensure you'll find any worn or weak spots in the air lines and an annual trip to the dive shop for overhaul on the regulator and a line inspection, should prevent any breakdowns or malfunctions. Adventure-Ocean