Diving with two tanks

[aquaregia]

I am sorry guys... I still dont get it

Why do you need two first stages? Why not connect the two tanks together (but still be able to open and close each tank separately) and use only one 1st stage?

One of the more likely ways to lose your gas is due to regulator freeflow. If you only have one regulator, a freeflow causes you to lose all your gas very quickly if you don't turn it off, but if you turn it off you don't have any way to breathe. If you have two regulators, and one freeflows, you can turn it off and use the second one.

 

[elmer fudd]

I am sorry guys... I still dont get it

Why do you need two first stages? Why not connect the two tanks together (but still be able to open and close each tank separately) and use only one 1st stage?

Nowadays, doubles are almost exclusively used by the tech diver crowd. These are folks who will be either diving in an overhead environment or with a decompression obligation. By having two first stages it allows you to keep breathing even if one of them fails.

It used to be that doubles, (and triples), were commonly used by divers who had no intention of going into decompression. They just either wanted more than 72 cf of air or they wanted a better trimmed or balanced rig. Things changed with the advent of single hose regulators and larger steel tanks however. With the old double hose regs you needed the regulator positioned down by your shoulder blades in order for it to breathe comfortably. This, (along with low pressure fills), limited the size of tanks available.

Now, you can get single tanks with capacities up to 149 cf. and even if you're a Hoover, that's enough air to keep you underwater for a long time.

 

[NC Wreck Diver]

The first 2 post manifold that became common was the Sherwood in the early 1970's:

The center post was retained so that it could be used with the double hose regs. The first two post manifold, that I remember, with both posts over the tanks was the Sherwood Genissis manifold which was used with the first 3500 psi steel tanks. These came out in about 1988/89 or so.

Wow.........Somebody has a picture of my first doubles manifold. We all dove Sherwood Selpac's. Ours were bought in 1986. I thought I would have to scan the Smithsonian to get a shot of these. Thanks.

 

[rcolsen]

This might be another head banging question but I have to ask it. If you needed to, could you remove your first stage off one trank and put it on another tank while under water? Or would this mess everything up. Of course I was planning on purging my second stage.

 

[AfterDark]

Is it possible to connect the two tanks and only use one regulator or do you need separate regulators, one for each tank?

OK, so you need two regs, do you use an alternate air source/octopus (four 2nd stages)?

Hehe, you guys must be banging your heads in the wall when reading this...

I use independent doubles with a regulator on each tank. I dive solo often and use a lot of gas. I use 2 regs no octo as the reg I'm not using is my octo. If one reg would fails (not likley) I'd turn around and abort the dive. If I'm doing a dive where aborting isn't an option then I'd add my pony bottle with a 3rd reg. I haven't needed to do that yet.

 

[a22shady]

as others said yes you can have 2 tanks hooked up together. You would need to use a manifold of some type. You do not need 4 second stages you would still only use 2, But would need to 1st staes. The reason for this is redundancy. If there is a malfunction or free flow with one of the regulators you can shut down that one Reg while switching to the other. So in a free flow you would turn the air off to the free flowing reg while allowing the manifold to still tranfer air from both tanks to the other reg. Here are some photo's of them and how some people dive them.

Manifolds

Manifolds are designed to connect two cylinders together to allow divers access to either or both cylinder. As divers continued to explore deep and overhead environments, it became necessary to maximize access to their gas supply, which was accomplished by attaching two first stages to one manifold. Should the regulator, o-ring, or hose fail, the diver merely shuts down the supply to that regulator, thereby preventing any further loss of gas. Because the valve knob nearest the regulator only controls flow to that first stage, the diver, through the manifold, still has access to the gas in both cylinders.

In the very unlikely event of a catastrophic failure of the tank neck o-ring or the burst disk, the diver can close the isolator valve and interrupt the airflow to that side of the manifold, thereby protecting the gas supply in the other cylinder. Manifolds should have barrel-style o-rings, no face seals, and should be adjustable. The 300 bar manifold provides more threaded depth and a more secure attachment. Valves should face straight, with no angles. Manifolds that place regulators at an angle increase their exposure and elevate the risk of breaking DIN connections.

 

[aquaregia]

This might be another head banging question but I have to ask it. If you needed to, could you remove your first stage off one trank and put it on another tank while under water? Or would this mess everything up. Of course I was planning on purging my second stage.

You would at least blow your SPG. I can't see any reason why it wouldn't work under Bob's "donkey's ass" scenario.

 

[NC Wreck Diver]

This might be another head banging question but I have to ask it. If you needed to, could you remove your first stage off one trank and put it on another tank while under water? Or would this mess everything up. Of course I was planning on purging my second stage.

Keep asking questions.........that's how you learn. We will worry about the Tylenol for the headbanging! The answer to your question is 'no.' Don't feel bad, we ALL asked this question as we started to dive doubles. If you are not asking questions, you're not learning anything. Post others if you like. That's what SB is all about. Safe diving to you.

 

[Aigtbootbp]

Hmmm....
I am just starting to dive a pair of old 53CuFt steels with an old USDivers manifold (the manifold I got from Paladin54 here) and I have to tell you the balance is perfect. Using those tanks on a backplate, a horsecollar BC, modern set of regulators and a 3/2 full wetsuit I needed no weight and no air in the BC to maintain perfect bouyancy. I felt much more free underwater, far closer to "flying" than ever before. It was great.

Reading this thread made me wonder. If someone were to connect two primary regulators with a short piece of hose via the HP ports, would that allow air to feed from both tanks?

 

[MikeSK]

I was thinking doubles would used for diving deep wrecks like the Speigel and such. Those arent on reg setups?

having to use two regs, you also need two computers yes? Kinda seems to defeat the purpose of having doubles.