Manifold failures

[James-S]

Hi Everyone,

At the moment I'm diving independent 12 liters, partly because I can't afford a manifold and also because I like having 2 completely separate gas sources. I've always reasoned that if for some incredibly unlikely event that something really heavy clouted the manifold then it would be possible that the seals at both ends of the manifold could go and lose all of the gas from both cylinders. However, I've been thinking - has this type of failure ever happened? Has anyone ever had, or know of a case where a manifold has completely failed and both cylinders were leaking gas?

Cheers for any replies

 

[DA Aquamaster]

No. Never happened.

The most likley "lose all the gas" with a manifold scenarios would involve blowing a burst disc and then not being able to isolate because:

1. You broke the isolator valve
2. Lost the knob off it, or
3. Are in a restriction where you can't reach it.

When I used to dive very cold water (32-35 degrees F), I preferred independent doubles - or a manifold with the isolator closed - as in the event of a freeze flow, while it was desireable to shut off the offending reg, it was not actually required. But it was also a moot issue as I never actually had a freeze flow under those conditions.

 

[RoyN]

Didn't have a failure of my manifold but my dive shop said my manifold's O-ring was going to blow so they fixed it. Just my 2 cent.

 

[halocline]

Didn't have a failure of my manifold but my dive shop said my manifold's O-ring was going to blow so they fixed it. Just my 2 cent.

Modern manifolds have either 2 or 3 consecutive o-rings on each side, so that all of the ones on one side would have to go for air to leak out that side. So I'm not sure what your shop was talking about.

When you're evaluating risk, you have to look at the likelihood of specific failures. Regulator failure is many times more likely than valve or manifold failure. If both regs fail on independent doubles, there goes the gas in both tanks. (Same is true, of course, for manifolded tanks) This is actually much more likely to happen than a manifold failing in at least two places, which is what's required to lose the gas out of both tanks. Logically, since the 'problem' that independent doubles addresses is the LEAST likely scenario BY FAR, the added safety is miniscule at best in that specific regard.

However, what is much more likely is a single regulator failure, and this is where manifolds do provide a distinct advantage, that being access to the gas in both cylinders. It's very difficult to successfully argue against this tipping the scale in favor of manifolds, from a purely mechanical perspective. Regulators are far more complex than tank valves, and must open/close hundreds of times each dives, while tanks valves get opened once. So designing a system to give maximum protection against regulator failure simply makes more sense.

There is the human factor, though, and operating an iso manifold adds a level of complexity and task loading. So there is an undeniable added risk, but I have no idea how you would calculate it. I know how you would minimize it, practice your valve drills!

 

[Cave Diver]

Hi Everyone,

At the moment I'm diving independent 12 liters, partly because I can't afford a manifold and also because I like having 2 completely separate gas sources. I've always reasoned that if for some incredibly unlikely event that something really heavy clouted the manifold then it would be possible that the seals at both ends of the manifold could go and lose all of the gas from both cylinders. However, I've been thinking - has this type of failure ever happened? Has anyone ever had, or know of a case where a manifold has completely failed and both cylinders were leaking gas?

Cheers for any replies

I seem to recall an incident involving Jill Heinreth where the van carrying their dive gear was in an accident, flipped and tanks got thrown clear. If memory serves me, a manifold was bent, but still held gas.

 

[PfcAJ]

I've personally bent two manifolds after they flew out of my truck bed. One of them looked like a shallow S. No leaks whatsoever.

 

[knowone]

A few leaks with face to face captured o ring crossover.
No leaks with triple o ring crossover, slightly bent.
No leaks metal to metal crossover, more bent.
No leaks metal to metal O2 type crossover
No leaks with rarely used suicide bars.
Leaks and bending contributed to by improper carrying and in the back on the bed sliding bashing and crashing and rocks and steel.

 

[Akimbo]

You probably won't need breathing gas anymore after experiencing an impact great enough to fracture a manifold — a body bag maybe. Invert one or both of your independent tanks valve-down if you are concerned over damage to your regulator hoses; and wear a hard hat.

 

[halocline]

You probably won’t need breathing gas anymore after experiencing an impact great enough to fracture a manifold — a body bag maybe. Invert one or both of your independent tanks valve-down if you are concerned over damage to your regulator hoses; and wear a hard hat.

+1. And stop diving in bomber ranges!

 

[Superlyte27]

I have a hat i'll lend you. It's got a brand new snoopy.