purposes of manifold

[H2Andy]

ok... i've been diving with doubles for a bit now, and
i've been thinking (and thinking) about the advantages
of a manifold

basically, i come up with one:

should one tank somehow blow, you can
isolate the tanks and prevent the contents of
the healthy tank from being drained away too

are there other benefits? other uses for the manifold?

 

[wedivebc]

ok... i've been diving with doubles for a bit now, and
i've been thinking (and thinking) about the advantages
of a manifold

basically, i come up with one:

should one tank somehow blow, you can
isolate the tanks and prevent the contents of
the healthy tank from being drained away too

are there other benefits? other uses for the manifold?

If you are asking what the benefits of the manifold over independants are then I have wondered the same thing. Basically I seen no benefit, in fact quite the opposite.
I do see a manifold (isolation) as a benefit to the old style without isolator but still see the independants as a safer setup than a manifold.
Although the risk of damage to a manifold is extremely rare I look at it this way. When the manifold is open, you have basically one large single tank until you perform an action, such as shut the isolator. With independants you have 2 isolated completely redundant systems that as long as you manage the gas properly will always get you home in the event of a failure.

 

[UTdiver]

Another benefit of having doubles with an isolator manifold as opposed to a set of independent singels is that you do not have to repeatedly switch which reg you are breathing from. If you are diving independent singles you would want to breath the air from each tank at the same rate. In other words, you would not want to breath one tank empty before switching to the other tank. For example, you might want to breath a third of the air from one tank, then switch and breath and third of the air from the other tank and keep switching back and forth so as to keep similar pressures in each tank. The reasoning for this is to avoid a situation where you have breathed one tank dry and then have a valve or first stage failure of the second tank and now you are underwater with no air. With a set of doubles and a manifold you automatically breath down the pressure in both tanks equally without having to switch regs and you can isolate one side if necessary. However, bot styles work and it mostly depends on the situation and what gear is available. Happy Diving

 

[scubafool]

Am I correct in assuming that you are comparing an isolation manifold to a non-isolation manifold?

 

[Hyper-limits]

One other benefit of the manifold is that you can breath the gas from both tanks from one post. Let say the reg on the right post start free flowing you isolate that post go to your back up regulator and you still have lot of gas to exit the water or get to your first deco stop. But saying that if you dive independants and use the right procedure you should have plenty gas left to safely return to the surface.
I use a manifold because I like the simplicity of it, you need to practice shut down to get it done quick, after all an Al80 will drain in about 80 seconds with a free flowing regulator.

 

[H2Andy]

Am I correct in assuming that you are comparing an isolation manifold to a non-isolation manifold?

hmm... welll... not really... but i guess you have to, by default, compare
the isolation manifold to its alternatives

i was basically thinking what the benefit(s) of the isolation manifold are

 

[WarmWaterDiver]

Although I'm not cave certified, I thought I'd chime in that I agree with wedivebc. We've discussed this a few times on this board, but never in the cave forum (for me at least).

The worst rig I think is that flexi-thing 'universal scuba manifold'. Hoosier and I agreed that at least the old 'cheater bar' things had rigidity.

http://www.scubaboard.com/showthread.php?t=122676

I dive independant doubles on occasion, and I've never had any problems with switching between tanks. Kind of gives 'on the job' training as part of the routine dive, rather than as a separate exercise.

 

[DA Aquamaster]

Manifolds with valves for each post protect you against regulator failures, while the isolator valve provides additional protection against tank related failures such as blown burst discs, neck o-rings, and manifold o-rings.

Gas management with independent doubles is actually pretty simple and only involves two reg switches. You breathe 1/3 from the first tank, then switch to the second tank and breathe 2/3rds from it and then switch back to the first tank to use the 2nd 3rd from it.

This means that at the mid point of the dive/point of maximum penetration you will have used 1/3 from each tank and will have 2/3 rds left in either tank. The implication is that if either reg or tank fails at that point, you have enough gas in the other tank to get you back out or to the first deco tank. It also means you will have a 1/3 reserve at the end of the dive.

The thing I like most about independent doubles is that if I have a freeflowing reg, there is no immediate imperative to do anything with it. As long as I manage the gas properly, if I lose all the gas in one tank, I still have enough gas in the other tank to get home. It's adviseable to close the valve on that tank and preserve the air, but it is not absolutely essential to do so. With manifolded doubles, you absolutlely have to close the isolator or one of the tank valves (depending on where the failure is at) or you will lose all of the gas in both tanks.

On the other hand if you have a reg failure with manifolded doubles, you can still access all the gas in both tanks. Just don't have the failure in a restriction where you cannot get to the isolator valve or you are screwed.

 

[WarmWaterDiver]

I liked the UK article using one tank of EAN36 and one tank of air for independant doubles flexibility - not something you could do with manifolded doubles (at least I wouldn't want to). But a great idea for 'travel mix - bottom mix' at places where manifolded doubles aren't handy to rent and the dive profiles aren't necessarily square.

http://www.scubaboard.com/showthread.php?t=122321

 

[scubafool]

hmm... welll... not really... but i guess you have to, by default, compare
the isolation manifold to its alternatives

i was basically thinking what the benefit(s) of the isolation manifold are

Well, if all you are interested in are the benefits of an isolation manifold, my take on it would be as follows.

An isolation manifold allows you to attach two tanks together and breathe the gas that they both contain from either of two regulators. These regulators are attached to two different posts, either of which you can shut off at any time.This allows you to shut off the gas supply to a regulator if it malfunctions, while allowing you to breathe all of the gas that both tanks contain from the other regulator. Independent doubles, worn on the back, do not offer this. Sidemount independents might possibly, if you are willing to switch regulators underwater. Not a nice thought, but better than the alternative. An isolation manifold also allows you to isolate the tanks one from the other, an invaluable quality in the admittedly unlikely event that a tank neck ring or burst disk fails. A non isolation manifold does not offer this option.

BUT there are a few potential drawbacks, BUT you only asked for the benefits.