re: Best Valve for Single Cylinder

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Genesis once bubbled...
has the Sea Elite manifolds at any time available for ~$160, in either 200 or 300 bar (choose - no difference in price)

Be careful with eBAY on these - you can often end up paying more in an "auction" than you'd pay just buying the darn things!

The ones on ebay are sold by divers supply.I have seen a few go with no bids or meet the reserve for 120.00.I have seen where divers supply sells them for 160.00 in their catalog.If i can save 40.00 bucks,ill be happy.

They also sell double 95's that include manifold and isolation valve,tank bands and bolts for 640.00.I wanted to get a set PST for doubles but may go this route and use a set of 108's.Anyways im still window shopping for now and keeping my eye out for any bargains.
 
and instead of an answer, get back blabber.

Where is this place Aqua?

And what is it about a tank configuration that leads someone to dive in a place or at a depth they are not qualified for?

Doubles are a perfectly legitimate open water configuration in some circumstances. I am going to try them out myself, not due to intending to do planned deco diving or the like at the present time, but because I often spearfish and when spearfishing we are often "same ocean" buddies more or less by necessity.

As such having a fully reundant kit on my back means that a single equipment failure is far less likely to lead to me needing to do a CESA from 110' - while I might well make it doing that, making it unnecessary is, for me, worth the (relatively moderate) expense and hassle. It also means that I can do two dives on one set of gas provided that I consume no more than half of the supply on the first dive; obviating the need to switch tanks and regulators on my kit during the diving day. The safety factor here is even better than you might expect; here's the logic:

1. I start with doubled AL80s each with 3000 psi.
2. If I was breathing one, I would likely surface with ~500 psi, or 1/6th the capacity of the tank, remaining.
3. If I dive doubles, instead of 1500 psi remaining, I will be surfacing with 1750 psi remaining, assuming I breathe the same cuft of gas.
4. The second dive therefore is commenced with about 93 cuft of gas, which means I have an even greater margin on Dive #2 than I would have by taking a second single full tank!
5. If for some reason I surface with insufficient gas (under 1500 psi) in the doubles, I not only have prevented an OOG emergency from happening on the first dive BUT I simply can skip the second dive or, if I have a third tank and whip on board, transfill the third tank into the doubles. Provided I can get over 1500 psi from that transfill I have sufficient gas for the second open-water dive.

So I win several ways:

1. I have a greater supply of gas, ergo, more time to solve problems underwater.
2. No single failure in my gas supply chain will lead to a need to do a CESA. I can shut down a failed post and in an extreme case isolate, even if my buddy is not within reach.
3. In the event of an inadvertant trip into deco land, I have the gas supply to manage the situation and complete the obligation.
4. In the event that my buddy has an OOA emergency for some reason, I have more gas on my back to give him/her.
5. I don't have to futz around with my kit between two dives on the same day; I can just put it back on and jump back in the water.

The disadvantages are:
1. I have to buy a set of bands (~60) and a manifold (~160 from Diver's Supply).
2. I will have to be satisfied diving the same mix (Nitrox) on two successive dives in the same day. This is not a major consideration from my perspective.
3. The kit weighs more out of the water and has more mass and drag underwater (possibly greater effort to propel myself.)

Never mind that getting comfortable with that configuration means that if/when I take formal decompression training I will be changing fewer things in my dive and will already be familiar and comfortable with the equipment I am using and its configuration.

If I can deal with the added weight and bulk of the doubled tanks underwater and on the deck I see no "lose" to this configuration and plenty of "wins" in the safety column. Since I don't dive on cattle boats whether the doubles will fit in some boat's tank racks is not a concern.
 
The potential downside to doubles or an H-valve is that there are more failure points. If you are skilled in valve manipulation it gives you options while if your not it just gives more places to spring a leak.

Genesis some caves won't let you use doubles unless your fuul cave traained.

I have geotten in the habit of diving my doubles almost all the time. I just like them (as long as I don't have to carry them too far) When I'm diving shallow like when teaching rec courses I can dive all weekend without a fill.

I might dive a single more if I had some steels that weren't doubled up. Aluminum tanks are no fun with dry suits and heavy wet suits.
 
Genesis once bubbled...
The issue with a single tank and "H" valve is that you do not have a truly-redundant gas supply. You can (yes, I know its a VERY unlikely event) lose the tank neck O-ring and neither of your regs will be usable.

Believing you have a redundant system when you do not is a bad idea. First don't fail catastrophically at a rate that is statistically significant. If you are covering the "one in a million" failure, then you need to be careful to insure that you're REALLY covering it, otherwise you're buying false security.

The "H" valve protects an extremely unlikely failure but leaves another extremely unlikely failure unprotected. That makes no sense to me.
The chances of a total gas supply failure are at least as high with manifolded doubles due to all the extra plumbing as they are with a single "H" valve, so the "not truly redundant gas supply" is a red herring. The chances of a total gas supply failure on either rig are so miniscule as to be no consideration beyond having a buddy anyway - and I know of ZERO instances of total gas supply failure with a single tank and "H" valve. Can you cite just ONE? There are documented total failures of manifolds, which would make the single/"H" valve more truly redundant than doubles! Just because your eyes see two tanks doesn't mean that gas is more secure than having it in one.
The catastrophic failure of a first stage is extremely rare, true - but that's not the failure mode we're really concerned with. The failure modes are (1) unstoppable freeflow (2) ruptured hose - all other failure modes are statistically insignificant - but either of those can be handled easily with an "H" valve rig.
Rick
 
is no more secure than is a manifold and I would argue that it trades one very unlikely failure for another, along with introducing a third problem that cannot be managed or controlled.

Both contain O-ring seals between the valves, and both can fail in virtually identical ways. There is one extra valve and one more double-O-ring seal in a set of manifolded doubles - right in the middle of the potential failure point (where the O-ring seals are between the valves), but unless the isolation valve ITSELF fails it PROTECTS the other failure points in the manifolds from becoming catastrophes. An H-valve ADDS a double-O-ring seal and then FAILS to protect THAT seal from becoming a catastrophe.

You are trading first-stage protection for a soft, unprotected connection between the valves.

I would argue it is a poor trade.

If you have a leak from the connector with an H-valve you're screwed as you cannot isolate the leak. This is exactly the same failure you are preaching about with a manifold's O-rings failing, except that you CAN protect the gas supply if it fails with a manifold.

Second and perhaps even more important, the H-valve leaves a rather heavy and nice lever-arm (the second valve and first stage) supported by nothing more than the double-O-ring connector piece. That's extraordinarily bad engineering. If you bang that against something you could lose the connector integrity, which is a catastrophic failure. A manifold which loses ONE SIDE is not catastrophically damaged (you can isolate it) AND the manifold is supported on BOTH ENDS, which makes it far more mechanically secure, as the largest thing(s) that are subject to impact (the first stages) are physically on top of the tanks (no lever arm to impart a moment to the crossbar and perhaps rupture its seals)

An H-valve protects against one very rare situation but introduces another failure of an equally rare caliber and fails to protect against the third "very rare" situation (tank valve O-ring failure.) It also, in an overhead environment, adds an unsupported and highly pressurized piece of hardware sticking out where it can be damaged, and leaves the diver no way to isolate the gas flow from that damage if it occurs.

In any situation where I might be "required" (by some agency, etc) to use such a valve I would argue that any safety gain is illusory at best and that the proper solution to the problem, assuming it is real in the first place, is doubles.
 
Genesis once bubbled...
and instead of an answer, get back blabber.

Where is this place Aqua?

And what is it about a tank configuration that leads someone to dive in a place or at a depth they are not qualified for?



(Big Sigh....)

Once Again, right or wrong, I didnt say I agreed with it....ANYWHERE in this thread!

Peacock and Ginney springs, are two that I know of, there may be more.
The reasons are based on wheather or not your proficient in roll off and valve shut down proceedures, before you go jumping into those caverns with your doubles?

Its not back blabber, its facts. But Im sure your YEARS of experience would know better huh?


Dave
 
That's nice.

I guess Ginnie Springs and Peacock don't want anyone who has a cavern cert, or who is taking training, in their cave system. Either you're "full cave" or you're not going to dive there with protected gas.

Fair enough - sounds like a couple of places NOT to patronize, provided you are accurately categorizing their policy.

I don't think you are.

Here is the link to Ginnie's diving policies:

http://www.ginniespringsoutdoors.com/dive.html

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.

It makes no sense to disallow a cavern diver, or any diver who wants to use it, use of a protected back gas supply.

As for "valve shutdown procedures", you are no less safe not knowing them then not having them available at all! A diver with a single tank who shuts down HIS (only) post has nothing to breathe at all! Finally, the right post doesn't roll off - it rolls ON. Simple physical reality here in the way the valve turns.

That argument holds no water; I fail to see how you can be LESS safe diving doubles, even if you don't know how to do valve shutdowns or isolations (you're no WORSE off than a diver with a single tank and valve in the event of a failure)
 
Genesis, sometimes I get crosseyed reading your stuff but it's worth it. The branched valves are peculiar, almost a Rube Goldberg (known for his hilarious and complex contraptions). Too bad that the industry doesn't make a narrow twin manifold that would allow a properly spaced, light weight set of small dia 45's for well heeled and safety conscious rec divers. Spearfishermen would like them, I bet. If there was a market, PST might be persuaded to make some 5.5 inch dia tanks out of 9791 alloy/3500 psi. That would give twin 60's with relatively low drag and reasonable weight. Regardless, if one needs a truly redundant rig, doubles are the real answer.
 
Genesis once bubbled...
is no more secure than is a manifold
Nor any less.
Find one failure.
Find one.
Just one will do.
Without one, all the "what ifs" in the world are without meaning.
Just find one single little total gas failure with an "H" valve.
Without a failure, there is no lack of redundancy.
Rick
 

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