O-Ring Questions

[rainmaker]

I just had a tank O-ring fail, luckily it was on the surface (when I was connecting my reg).

It started me thinking; how common are O-ring failures at depth? Anyone here ever experienced one? If so, could you describe what happened?

 

[miketsp]

This subject has been well discussed in various threads, often under the subject of din versus yoke comparative reliability.
When it happened to me at 25m I didn't realise what was going on at first, there was just this tremendous noise as if there was a high revving motorbike right behind me and I was looking for the source. Then when I rolled on my back and saw the enormous cloud of bubbles going up I realised what it was.
My buddy was close by with an alternate air source so no problem.
It does actually take some time for the tank to empty, over 1 minute so no need for immediate panic.

 

[contengo]

The o-ring failure I am used to seeing is during installation. Wrong threading will slice the o-ring bad enough.

 

[String]

It does actually take some time for the tank to empty, over 1 minute so no need for immediate panic.

That does really depend when on a dive it happens. Although not O-ring failiure my tank emptied in about 30 seconds or less purely because it decided to happen near the end of the max depth portion of the dive where there was only about half the gas left

 

[Dive-aholic]

I just had a tank O-ring fail, luckily it was on the surface (when I was connecting my reg).

It started me thinking; how common are O-ring failures at depth? Anyone here ever experienced one? If so, could you describe what happened?

This is why the first thing I do is set up my rig and turn on the air. If it's going to fail, I'd rather it fail on the surface. All too often I hear other instructors tell students to turn their air off until they're ready to get wet, or see DMs on boats go around and turn air off until arrival at the divesite. Turn it on and leave it on.

 

[dougaldiver]

I always turn the air on, check that everyting works (breath from regs, check inflator) and then turn it off but leave the system pressurised.

This means you can check for small leaks by seeing if the SPG drops over a period of time, it also means that, if you do have a leak in the system the only air you will lose is what's in the regs. (I learned this from experience in my early diving days. Turned the air on and left it on until it was time to dive. When I came to kit up just before the dive I checked the SPG and the tank was only about a third full, the rest had leaked out. Fortunately there was another tank available and it was just a bit of a panic changing it over in time to dive.

 

[DA Aquamaster]

Dougaldiver is on the money with the pre-dive on and off pressurization check. It suitably stresses the o-ring so that if it is going to fail it will most likely do so on the way to the dive site and it provides a very sensitive leak check to the entire regulator and valve system.

Many people compare DIN and Yoke and claim DIN is superior as the o-ring is fully contained. DIN is a superior connection from a mechanical stanpoint point and I have personally screwed up badly and allowed my doubles to fall off the bench plant themselves head first on the deck in rough seas with no damage at all. Things would have broken or come loose with a yoke valve.

But to be fair to yoke valves, a properly designed yoke connection in good condition and propery connected will have the same very close tolerances and will in effect also have a captured o-ring. The ones I see fail are either cut or they extrude because the yoke connection was not properly tightened.

In 20 years of diving and probably 1700 dives, the majority of them with yoke valves, I have never had more than a slight leak develop underwater from a tank valve o-ring. In my expereince, if it fails it will fail when it is pressurized or shortly after and will almost always be due to damage or improper installation of the yoke on the valve.

 

[Warren_L]

I always turn the air on, check that everyting works (breath from regs, check inflator) and then turn it off but leave the system pressurised.

This means you can check for small leaks by seeing if the SPG drops over a period of time, it also means that, if you do have a leak in the system the only air you will lose is what's in the regs. (I learned this from experience in my early diving days. Turned the air on and left it on until it was time to dive. When I came to kit up just before the dive I checked the SPG and the tank was only about a third full, the rest had leaked out. Fortunately there was another tank available and it was just a bit of a panic changing it over in time to dive.

I do this too. Pressurize the system at first to check for leaks. And depending on the situation, I may or may not turn the system off. But to add on to this, it is always then doubly important to check your valves before the dive and breath from both second stages while looking at the SPG, which is part of my normal pre-dive check anyway.

 

[String]

I tend to pressurise in car park, test breathe (taste ok, check contents etc) then turn off leaving system pressurised. That way water wont get into the regs even if its a rough boat journey as theyre pressurised and if the kit falls over or gets a knock it cant leak out all your air en route as the cylinder is off.
As an added bonus, if its an unusually gentle journey, check SPG on arrival at dive site and if contents gauge still showing a full tank then you know there are no leaks in the system.

 

[Scottri]

I've never had one fail under water. I've messed a few up on the surface over the years but I've never seen one fail under water.