Double tank setup?

[Aigtbootbp]

Correct me if I am wrong but I have heard one way to set up a double tank rig is simply to have two tanks, each with their own regulators. I guess this would be attached to an appropriate bc/backplate and when one tank runs down you simply spit out your regulator and switch over to the other.
Is this correct?
Of course I figure each tank would have it's own SPG. I guess the BC would be connected to one of the tanks.
Thanks

 

[jim2386]

Correct me if I am wrong but I have heard one way to set up a double tank rig is simply to have two tanks, each with their own regulators. I guess this would be attached to an appropriate bc/backplate and when one tank runs down you simply spit out your regulator and switch over to the other.
Is this correct?
Of course I figure each tank would have it's own SPG. I guess the BC would be connected to one of the tanks.
Thanks

Not quite.

You wear two tanks that are connected at the valves with an H valve. This allows you to get all the air out of both tanks with one regulator. Each tank valve itself has it's own first stage and second stage. You get one SPG coming off the left tank. Each tank has it's own valve. When you close the valve, it cuts air off above teh H -valve. This means that if you have a free flow and have to shut down a regulator, the other regulator still has access to all the air in both tanks.

On the middle of the H-valve there is an isolator valve. This can be closed to seperate the air in both tanks. The only time that you really would ever use this is if a leak happened below the shut off valve on one of the tanks. This allows you to use the air in at least one of the tanks and keep it isolated from the leaking tank.

In summary....typically.....two tanks connected by an H valve to form one big tank. Each tank has a first stage and second stage. The valve on each tank can shut off each regulator independantly. The isolator valve in the middle can be shut to isolate one tank from the other in an emergency where perhaps you blew your o ring between your tank valve and physical tank.

 

[vjanelle]

Jim, that's twinset with a manifold. You can also dive two tanks independently, switching them out every 500psi or so. If you only breathe one tank down however, you'll find yourself quite lopsided.

Twinset diving with a manifold has additional failure points which you can manage (see the nine failures), or you can dive with a stage bottle (just another AL tank you breathe down and switch out to your back gas when you're done), or sidemount.

 

[jim2386]

Jim, that's twinset with a manifold. You can also dive two tanks independently, switching them out every 500psi or so. If you only breathe one tank down however, you'll find yourself quite lopsided.

Twinset diving with a manifold has additional failure points which you can manage (see the nine failures), or you can dive with a stage bottle (just another AL tank you breathe down and switch out to your back gas when you're done), or sidemount.

Let me clarify.

What I described above is what I dive. As stated, there are other setups as well.

 

[Paladin]

My doubles rig is made up of two steel 72s, each with a Genesis K valve. Connecting the two tanks is a crossover bar (with a yoke at each end) with a center tap where the regulator is attached. This gives me the option of quickly breaking the set back down into singles, should the need arise, without having to empty the tanks.

 

[Bonairetrip]

There are many ways to carry and utilize more than a single tank (as others have alluded to). There are stage bottles (tanks that are clipped off of your harness d-rings using bolt snaps), there are side mounts and the more common doubles.

Within doubles, there are the two independant tanks and those connected via a manifold that has an isolator valve. The advantage of the second set-up is that you can dive with the tanks connected. This uses each tank equally (keeping you in trim). The valve allows you to colse off one side if the need arises (such as major airloss coming from one set of regs. There are a few downsides: cost and converting a tank back to a singles set is more work. There is also the risk that you might accidentally close the islolator valve when you did not mean to. I don't think any of these issues are a huge deal.

For SPG, my rule is simple: I have a pressure gauge for every tank I take with me.

Most doubles sets I have seen use the manifold. So the tanks are joined both by the manifold and by some doubles bands. The doubles band then mounts to the backplate. The backplate is attached to the diver by a harness. And the air cell or wing (the flaoty part of the bc) attaches to the backplate.

It sounds way more complicated than it is. But creating a set of doubles is pretty spendy. Lets assume you already are using a back plate and wing as your BC and you currently have only one reg set and no suitable tank. No need to replace the harness, plate or reg or tank. (Note: IMHO, tanks should be of matched brand/model and size)

So, about $150 for a nice set of bands. Around $200 for a manifold. Another $250 to $300 each for two steel tanks. So at just less than $1k you have your set of doubles.

But wait, another $300 give or take for a nice doubles wing. Then, ideally, you add another reg first/second. Lets say you go about $450 for that. Oops, and that extra spg for about $80. At this point, many divers if they want to also have a singles set will buy another plate and harness.) These are all new prices.

OTOH, over time, many divers (most?) accumulate gear. Many already have that second tank, that second reg set and that second spg. For them, the cost is much less. And there is always the used route as well....

 

[Paladin]

My doubles setup didn't cost me much at all. I bought two matching steel 72s for $50 each off Ebay. Both were in fresh hydro and only needed visuals, which they passed with no problem. I bought a set of bands (the type that have the rubber insulator bands and are designed to work with a vintage plastic campac) off Ebay for $35. I bought an 8 1/2" crossover bar with a center tap off Craig's List for $30. The seller threw in a set of vintage bands which I have stored back in case I want another set of doubles. To use the crossover (cheater) bar, the tanks needed to have identical valves, so I purchaseed a pair of new Genesis K valves from Leisurepro for $45 each. I converted my old Healthways Campac to doubles by bolting the bands onto it at the attach points molded into the plastic backpack. I slid the bands over the the tanks (with the new valves installed) and positioned them loosely. Next, I connected the crossover bar between the two tanks and tightened the yokes at either end to the valves. I double checked the stance of the tanks, then snugged up the bands. The last thing to do was to connect a regulator to the center tap and turn on the air (both tanks) to check for leaks. Total assembly time; 20 minutes. Everything checked out and since then I've been in the water with them four times with no problems.

I prefer diving with steel 72s but a pair of matching AL80s would also work.

Total cost, including shipping: $340.

This rig gives me several options.

1. I can dive it the way it now sits, using a single regulator attached to the center tap of the cheater bar the old fashioned way. This is my preference as I mostly dive using my 1959 USD Aqua-Master double hose reg.

2. I can loosen the bands, remove the crossover bar, reposition the tanks and dive the rig as twin singles with a regulator on each tank.

3. I can disassemble the rig into singles and return the backpack to single configuration and dive the tanks as singles.

With the crossover bar connecting the tanks at the K valves, there is no need to remove the valves or drain the tanks when switching configurations.

I use a horse collar BC (on the rare occasions when I use a BC at all) so changing BCs isn't even a consideration for me.

 

[ams511]

Guys, the OP could be talking about a sidemount setup.

 

[Paladin]

Guys, the OP could be talking about a sidemount setup.

Hmm. You know, you could be right. I honestly hadn't thought of that.

 

[knowone]

Both tanks are banded to each other using steel or webbing, which is more convenient and attached to the bcd. Spit out regulator every so often to breath tanks down evenly in case your catastrophic failure occurs with the full tank and of course trim. I dive with tanks and one of my legs is shorter than the others.