What fails in the gas delivery system

[jhelmuth]

:06: What fails in the gas delivery system (IE - the mechanical only failures in OOA situations)? If you have a reply, please state whether this failure actually occurred in your presence, or if it's this a story you heard about.
As I am becoming more-and-more familiar with the gas delivery equipment (Cylinder/valve/1st & 2nd stages/SPG), I "sense" that OOA due to equipment failures are rare within recreational limits (I don't not consider extreem coldwater dives in this catagory - for me, anything colder than 60 is not within my training/experience). I have no facts to back this up - just a guess. This is significant to me as I consider when/where I want to use my 19 cu.ft. pony (once I buy it) rig.
The pony is virtually for myself and my buddy, so I understand that we'll have to remain vigilant in making sure that we don't have failures due to human error (it could happen - I know).

 

[scubatim77]

If you are talking about out of air situations only, on the rare occurance of equipment failure would be traced back to faulty guages, or a battery going dead in your computer. O-rings could give way if annual serviced isn't performed (or it is incorrectly), hoses could burst. Most commonly, even in cold water, it is diver error that causes OOA situations. If you properly maintain your equipment, and have high quality equipment, you shouldn't have any problems. As a side note, in cold water, versus warm water, dive preperations will prevent most any accident. These things I have listed I know as I work on eqiupment almost on a daily basis.

 

[jhelmuth]

I certainly was not thinking of equipment which was not maintained. I guess that would be true, but I can't imagine any reasonable diver even considering using equipment which was not properly maintained (especially if it belongs to them), and I'd certainly inspect any rental equipment sufficently. If I thought it were suspicious, no way would I dive with it.

I was looking more at reasons for gear failure where reasonable maintenance was taken. I've hear the stories of a hose bursting ( at least on the posting on this board). Does that happen often? Should you not notice a hose which is "ready to blow" by visual and physical inspection?

 

[Padipro]

I've been diving for over 20 years and in all that time I can't remember ever seeing a hose burst, not once. The most common thing I've seen fail is a tank valve to regulator O-ring, and that's why all my tanks and regs are equiped with DIN valves and adapters. The O-ring is captured inside the valve and is far less likely to fail even under the most extream conditions.

 

[RiverRat]

I'm a fairly new diver here but I would tend to think the tank O-ring is a common failure point. Take a look at my avatar, see the bubbles streaming out from my tank I wanted to replace this O-ring as I spotted the slight leak on the boat, but of course NO one including myself had any spares. The rental tanks really take a beating. Lesson learned, carry spares of everything and don't expect the dive op to have any spare gear.

 

[mddolson]

I agree with you Scott. In my 32 years (guess that makes me old) of diving I too have never seen a hose blow. They do leak around the crimped threaded connections and I have seen a large bubble under the outer jacket burst and then create a steady steam of bubbles. But an out and out burst, NOT!

My only valve/regulator failure was my own stupidity.
I had only been diving two years. we were diving on the Wetmore, in 30 ft water, Fathom Five park, Tobermory, Ontario.
There were some cool openings you could swim through, and even spots where you could push off with your legs and sort of shoot through some arches. (This was before I got educated about the damage I was doing to the wreck).(This is no longer a possibility, storms and diver traffic have pretty well flattened the wreck, only her boilers still stand) I did one of those push-off and glide maneuvers, and didn't quite get low enough and I cranged the yoke hand wheel of my regulator on something. Well I hit it hard enough to bend the yoke and tilt the hand wheel to about 30° out of alignment. The oring seal burst of course and I had full tank pressure roaring out of the valve. I was only in 30 feet of water so I sam to the surface and shut of the tank. BUT the First stage was garbage. It was a USD Calypso 4, which has a cast yoke. I attempted to straighten it in a machine shop, but it cracked when I did.

regards

Mike D

I've been diving for over 20 years and in all that time I can't remember ever seeing a hose burst, not once. The most common thing I've seen fail is a tank valve to regulator O-ring, and that's why all my tanks and regs are equiped with DIN valves and adapters. The O-ring is captured inside the valve and is far less likely to fail even under the most extream conditions.

 

[jhelmuth]

While this is not conclusive (yet), it seems like there is some concensus that properly maintained "gear" (gas delivery system) does not fail much (if at all) beyond the occassioinal worn oring. I've seen that too (why didn't I think of that) in rentals. Not often, but frequently enough. I'd say that in those instances, they were not life threatining, just a nusiance and a waste of gas.
I'll keep following along, but post my next question about "where/when" to strap on the pony.

Thanks to all so far, and those of you who might offer some additional insight!

 

[pipedope]

in one season.

There was no warning on one, just POP and HISSSSSSS!
The other one showed a bubble a few minutes before blowing.

No big deal, change the hose and finish the job in the first.
In the second I didn't have a spare hose at the job site so I removed the hose and put a plug in the first stage so I could finish the job.

I could have finished the job in both cases with the slow leak from the HP hoses but the noise would have had my tender ready to kill me by the time we were done.

The most dangerous time for a mechanical failure of a regulator is right after it has been serviced. Most failures are due to assembly mistakes.

 

[Brian1968]

I'm a fairly new diver here but I would tend to think the tank O-ring is a common failure point. Take a look at my avatar, see the bubbles streaming out from my tank I wanted to replace this O-ring as I spotted the slight leak on the boat, but of course NO one including myself had any spares. The rental tanks really take a beating. Lesson learned, carry spares of everything and don't expect the dive op to have any spare gear.

What locale was this? Was it a typical dive charter company...two tank dives and all that?

If so, it's odd that they had niether extra tanks nor extra O's.

Like you say, the rental tanks take it pretty bad oftentimes, but they do belong to the charter company it's up to them to make sure they have more than adequate reserves on board.

Just my thoughts.

 

[miked]

I heard,then saw, a HP hose "burst" -again once in many years of diving. It was on rental gear, and it was quite an event. I was about 10 'away, and I heard the "pop", and the air. The air escaping looked like the surface bubbles in a hot tub.The diver wearing the rig got quick help from his buddy-a DM: an octo and a safe trip to the surface.
After the dive, the diver involved said "it sounded like a firecracker".
I saw the hose, it had a split near the connection to the first stage.

Mike