Reg Failures

[Teller]

This isn't going anywhere. Never mind.

BTW, neck o-rings and burst disk are not reg failures they are valve failures. I don't know why people keep mentioning them. Obviously if the valve on the cylinder cant hold pressure than that's a problem with the valve.

 

[halocline]

Manifolded doubles do have additional redundancy vs independent doubles IMO. The reason is that in the VAST majority of cases, a free flow would be caused a reg failure or possibly something in the valve. Burst disc and manifold failures are VERY rare. In the case of a reg failure, you still have access to the gas in both tanks. This means that with a manifold, you are far less likely to lose half your gas than with independent doubles. I think it's perfectly reasonable to consider that additional redundancy.

In the case of both a bust disc/tank neck o-ring failure AND a manifold failure, yes you would lose all your gas. To my knowledge, that scenario has not happened in the real world, although it happens on every single thread discussing this very topic.

I'm sure there are other reasons that sidemount is as popular as it is; trim considerations, easy travel, super easy valve access, but I would not dive sidemount for any perceived increase in safety due to independent tanks. Just my opinion....

 

[Teller]

Manifolded doubles do have additional redundancy vs independent doubles IMO. The reason is that in the VAST majority of cases, a free flow would be caused a reg failure or possibly something in the valve. Burst disc and manifold failures are VERY rare. In the case of a reg failure, you still have access to the gas in both tanks. This means that with a manifold, you are far less likely to lose half your gas than with independent doubles. I think it's perfectly reasonable to consider that additional redundancy.

This is exactly why I am asking this question. You say BM has more redundancy then SM due to the fact that in SM I can loose half my gas if I have a reg failure. I am not sure if I am asking the question clear enough but I will try again. With SM a free flow can be dealt with by feathering the valve and breathing off of the free flowing reg. Knowing that I would like to know what can happen to make a reg not work completely (you can not breath from the reg at all, no free flow). I understand the debris blocking the dip tube and the tank neck o-ring and burst disk but those issues apply to BM as well so lets forget those for right now. One person mention a cracked/smashed second stage. I would imagine that smashed second stage would result in a free flow. Is that not correct?

 

[ianr33]

I would imagine that smashed second stage would result in a free flow. Is that not correct?

No, I don't think it is.

If you crack the body of a second stage there's no reason for it to freeflow. What will happen though is you may be sucking more air than water when you do inhale. If the diaphragm is nor correctly seated you get the same thing. (Been there done that! )

I think the answer to your original question is that although it may be possible for a reg to suddenly stop delivering gas, the chances of that actually happening are vanishingly remote. So I agree with you the "you can lose half your gas in sidemount" argument is a little overdone

Personally I know I feel safer in sidemount. With appropriate gas planning any single failure can not be life threatening,you don't even have to do anything to fix the problem or close any valves. Just turn the dive and head home. That gives me a warm fuzzy feeling.

I know lots of divers that will do solo cave dives sidemount. Suspect very few would do those dives backmount. (at least without a stage/buddy bottle)

 

[dumpsterDiver]

This is exactly why I am asking this question. You say BM has more redundancy then SM due to the fact that in SM I can loose half my gas if I have a reg failure. I am not sure if I am asking the question clear enough but I will try again. With SM a free flow can be dealt with by feathering the valve and breathing off of the free flowing reg. Knowing that I would like to know what can happen to make a reg not work completely (you can not breath from the reg at all, no free flow). I understand the debris blocking the dip tube and the tank neck o-ring and burst disk but those issues apply to BM as well so lets forget those for right now. One person mention a cracked/smashed second stage. I would imagine that smashed second stage would result in a free flow. Is that not correct?

No that is incorrect. Why would a smashed second stage necessarily free flow? A 60 second examination of a second stage would reveal this fact?

 

[Teller]

No that is incorrect. Why would a smashed second stage necessarily free flow? A 60 second examination of a second stage would reveal this fact?

Ok so then I guess a smash second stage would result in a catastrophic failure. Is there anything else?

 

[Fishpie]

Broken or dislodged demand lever.
Broken spring in 1st stage.

........will result in no or very little gas.

I have had both happen.

 

[halocline]

Torn/folded diaphragm or exhaust valve would be another. Anything that causes the 2nd stage to flood. I also would not assume that the debris in the tank is the same for manifolds and independents. The dip tube is a big opening; small debris could easily (and does)pass through it and get into the filter in the reg, which clogs much more easily. In that case, the manifold still gives you the gas in that tank.

You're making a lot of assumptions IMO. I would not assume that you can feather the tank valve successfully in all cases of reg failure; maybe in some, but I wouldn't count on it. I'd also just pick sidemount vs backmount based on what configuration you like diving more, not on any perceived safety margin based on 'what ifs.' Both systems have proven to be very safe, with good training and dive behavior. Sidemount is very hip these days; but lots and lots of great divers use manifolds in all sorts of extreme environments.

BTW, you're worried about "losing" your gas, not "loosing" it. It's already "loose" in the tank....

 

[redacted]

BTW, you're worried about "losing" your gas, not "loosing" it. It's already "loose" in the tank....

At my age, I think I worry about loosing it more than losing it.

 

[Couv]

......I would like to know what can happen to make a reg not work completely (you can not breath from the reg at all, no free flow).....

My DIY friends will have a good laugh at my expense on this one. My very first regulator service attempt caused a complete failure to deliver air. I did not torque down a jam nut on an old Dacor reg and it resulted in the orifice putting so much pressure on the second stage seat no air could flow.

Here are few threads that mention failure modes that fit your criteria:
Warning! Scubapro MK 10 fault [Archive] - ScubaBoard
Scubapro MK20 Cracking Problem Deepens: Undercurrent 08/2005

And one that got the attention of a few of us the: MK 5 turret retainer failure.
http://www.scubaboard.com/forums/regulators/173774-complete-1st-stage-failure-scubapro-mk5.html