re: Best Valve for Single Cylinder

[Rick Murchison]

What are the most common types of gas delivery system failures?
Number One: Unstoppable freeflow (lots of reasons - why doesn't matter - it's number one) - All I can draw on is what I have seen - and using that as a basis I'd say this is way out front of all other gas supply system failures. Solution - shut down that reg. "H" valve or Doubles, same solution.
Number two: Hose failure (2A) high pressure spindle failure - second to uncontrollable freeflow - not as common but far more common than (2B) - LP hose failure or (2C) HP hose failure. Solution - shut down the affected reg. "H" valve or doubles, same solution.
These are the failures you're likely to see in your diving life. (One more, the Yoke O-ring failure is possible if you dive Yokes, but if you're diving doubles or H valves you oughta' be diving DIN) Failures you can dream up but you're unlikely to see or even hear of are a catastrophic first stage failure, or a busted manifold (I have seen one busted manifold - the manifold itself was banged into a beam on a wreck and both sides started spewing air) - and I have *never* seen or even heard of an extruded tank o-ring on a properly maintained and filled tank - indeed the only place I've ever even heard of an extruded tank o-ring has been on this board. (On my list of experiments to perform is to rig a tank with no o-ring and fill that sucker up & see how fast it leaks - I'll bet it isn't very fast)
Bottom line - you are no more likely to suffer a total gas failure with a single/"H" valve than you are with a double/isolation manifold system. So there is no reason to use doubles other than a need for the extra gas. If you don't need the extra gas, carrying doubles makes no sense when you could carry a single with an "H" valve.
Rick

 

[Aquamaniac]

Genesis once bubbled...
That's nice.

They prohibit lights if you do not hold a cavern or cave cert, but nowhere is it mentioned that you cannot use doubles unless you have a full cave certification.

I think I'll call them in the morning.

Perhaps before you make a fool of yourself, you should re-read my post.......
When did I mention you needed full cave to use doubles at Ginney?............

 

[Aquamaniac]

Furthermore, from the link that YOU posted....


Ginnie cavern is among the handful of sites that experts consider sufficiently safe to allow exploration by divers who lack formal cavern or cave diver training. Certified divers of all experience levels may take lights into the water with them at Ginnie Spring and use these lights to explore the underwater cavern.

I think you are getting Devils and Ginney mixed up, but thats OK, I wouldnt expect you to understand.........

 

[kcanty]

The limits are mainly concerned with one issue.

Also they are only for cavern and cave intro level divers.

The progression is : cavern, intro, apprentice,
and full cave for most agencies.

The issue with doubles is the amount of air supply
carried. I have the equivilant of 4 al80's on my
back when I wear my LP120's ( 320cf ). That's a lot of
gas.

A cave-intro diver can have as little as 4 cave
dives all of which are with an instructor. A lot
of people consider the ability for an inexperienced
cave diver to have a huge air supply to penetrate
very deep into the cave system to be an accident
waiting to happen. Thus the prohibition.

BUT, there is also the possibility of having an auxiliary
form, based on your instructors discretion, which allows
the use of doubles at the intro level. Intro divers
using doubles also need to follow the rule of 1/6ths
not 1/3rds.

Also by the way, there is a training path which allows
the use of doubles starting with cavern, again at the
instructors discretion. There is an added caveat with
this path as it requires that full cave be achieved within
a set period of time which I think is 1 year.

Hope this helps clear up this issue a bit.

Kell

 

[JeffAustin]

I like being able to go from singles to doubles and have the same reg. configuration. For me, the" Y "works better than the "H". If they were just available in any kind of quantity, that's the problem, getting your hands on them.

 

[Genesis]

There's not all THAT good of an argument for "littlle tanks". You can double a pair of HP80s and have a small, lightweight package (comparatively) with a lot of gas. The ability to do two recreational dives on one set of tanks without having to touch your rig is a plus. Having the gas to be able to have "an issue" (such as going into deco inadvertantly, or having a problem you can isolate and solve underwater) and be ok is a pretty significant safety enhancement.

I have a friend who has dove on my boat a couple of times with TRIPLE little US Divers (old, old, old!) tanks with a screwball manifold in a flattened "V" configuration. No isolators though.

Its a unique set of tanks and bizarre looking, but the guy has three sets of them and likes the trim and balance.... they gotta be 20 years old....

For spearfishermen I would think the PST HP80s would make a great choice doubled up (you could do the 65s, but they're only 2lbs less in dry weight - probably not significant.) They're -2.5lbs empty, so figure -5 for a double set. Assuming another couple of lbs for the bands and manifold - maybe -7 or -8 total. That means that for people with a moderate level of exposure protection (e.g. 3 mil full wetsuit) and a light (Aluminum) backplate you'd need ZERO lead and even with a fairly heavy amount of exposure protection the weight requirement would be moderate. They'd be too negative for safety for someone diving in a skin or bathing suit - but if you're spearing, you probably want some exposure protection anyway, even if just for abrasion protection around wrecks and rocks, and I find that even in the warm summer water a 3 mil suit is fine - I don't overheat.

The HP100s are STILL shorter than AL80s. Those, doubled, would be "the bomb" for spearing, I'd think. You could do virtually any pair of dives with a reasonable SAC on those within no-deco limits on EANx32 and not run out of gas. The only problem is the additional 5lbs of weight (each); now the kit is starting to get a bit heavy.

 

[Aquamaniac]

Thanks for the Clarification Kell

 

[MikeFerrara]

Rick,
What about a burst disk? I have seen them go.

 

[wetlettuce]

Thanks for the advice.

My reasoning was to protect from a first stage or second stage free flow particularly as we are now in winter diving mode in the UK.

I usually dive with a 15l steel and a 3l pony attached to the tank. In the move to DIR the pony position must change and I was thinking of dropping it altogether.

I aim to move to doubles within the next six months (twin 10's (we measure in litres)) but will do some training first (Advanced Nitrox IANTD)

I was thinking that a H valve may be useful for some training or practice before i moved to doubles.

I 've decided to use a pony if required as a stage cylinder on the left side as per DIR. The H valves don't really seem to help a lot and so I'll save the money.

Thanks for your help.

 

[Rick Murchison]

MikeFerrara once bubbled...
Rick,
What about a burst disk? I have seen them go.

I've seen 'em go too - during an overfill, and a tank in the sun. Never seen one go once the tank's in the water - but I suppose one could. I put that kind of failure (along with the extruded tank o-ring and the ruptured tank) somewhere between the likelihood of having a triple light failure and getting struck by lightning on a clear day. If I'm worried about that one I'd best stay out of the water, off the road and indoors. Still, I do take a buddy along.
Rick