double tank equipment

[agilis]

Many years ago I had a set of double 40cf bottles, with only one open/shut valve, centrally located. They gave me a bit more air than my 72cf, but more importantly they were much better balanced.

I've tried to replace them, but every manufacturer seem to make these complex double isolation valves for technical diving when all I want is a double that does not provide additional air, just better weight distribution and balance on my back.

The only spg needed was, of course, attached to the regulator. My little bail out bottle had its own regulator and spg.

I really wish I could replace that old unit, perhaps updated with a din regulator mount, just one for both bottles, something simple and strong. It was really wonderful for recreational diving.

 

[jcaplins]

I really wish I could replace that old unit, perhaps updated with a din regulator mount, just one for both bottles, something simple and strong. It was really wonderful for recreational diving.

one of theses?:
XS Scuba PVD Manifolds

 

[Storker]

Why do you encourage irresponsible behavior?

How is my clubmate's 232 bar D7 (~110 cuF) irresponsible while my other clubmate's 300 bar 12 (~115 cuF) is responsible? How is my clubmate's 232 bar D8.5 (~135 cuF) irresponsible while the 300 bar 15 (~145 cuF) that I just sold (since I don't need that amount of gas and it was a b!itch to haul and stow) is responsible?

Tanks aren't behavior. Doubles doesn't necessarily mean lots&lots of gas. And if you dive dry in cold water, you just might need more than an Al80 to last you an hour's worth of responsible no-deco diving, within both NDLs and min gas. I use some 25-30% more gas when I dive my trilam suit in my home waters than if I dive a 5 mil wetsuit in warm waters, and my 300 bar 10 (~100 cuF) holds just enough to approach no-stop limits if I don't have a bad air day.

 

[agilis]

one of theses?:
XS Scuba PVD Manifolds

View attachment 210687

Wonderful! Exactly the manifold of my dreams. Thanks again. Are 5.25 double bands available, able to fit on a BCD or a simple plate with wings? I have my old set mounted on a vintage back plate, but something new and sturdier that would allow the use of buoyancy control might be preferable.

I've tried side mounts, but because I try to stay as sleek and as close to the feeling of free diving as possible, they were not for me.

At 73, I'm getting close to aging out of diving, one way or another. I can't handle heavy tanks as effortlessly as I once did without pulling some damned muscle or another. I'd like to try twin aluminum 40s over the coming decade or so that I might be able to squeeze in.

 

[Adobo]

How is my clubmate's 232 bar D7 (~110 cuF) irresponsible while my other clubmate's 300 bar 12 (~115 cuF) is responsible? How is my clubmate's 232 bar D8.5 (~135 cuF) irresponsible while the 300 bar 15 (~145 cuF) that I just sold (since I don't need that amount of gas and it was a b!itch to haul and stow) is responsible?

Tanks aren't behavior. Doubles doesn't necessarily mean lots&lots of gas. And if you dive dry in cold water, you just might need more than an Al80 to last you an hour's worth of responsible no-deco diving, within both NDLs and min gas. I use some 25-30% more gas when I dive my trilam suit in my home waters than if I dive a 5 mil wetsuit in warm waters, and my 300 bar 10 (~100 cuF) holds just enough to approach no-stop limits if I don't have a bad air day.

I think the point was that someone who doesn't know much about doubles should get some instruction from someone who is qualified to provide instruction.

There are different ways to implement doubles. The one I am most familiar with (using an isolation manifold) requires some knowledge from the divers part to dive safely. For example, isolator position is of consequence not only while diving but also when filling. I've had situations where a dive shop closed the isolator prior to filling the tanks. And I once inadvertently closed the isolator at the beginning of a dive.

Also, there are just some basic things like how to configure regulators, how to route hoses, etc that is best done through instruction as opposed to a newbie having to rediscover the wheel.

And this is just for a doubles set up with an isolation manifold which is in my opinion, the least complicated doubles set up. (Less complicated that independent back mount doubles or side mount). I imagine there are more procedures and gotchas to sort out with the other types of doubles set ups.

Finally, regarding the quantity of gas... just because you and your friends don't dive with relatively big doubles doesn't mean that that is not the intent of the OP or others who read this thread subsequently. Therefore, it seems the prudent thing to do is to suggest that any inexperienced diver thinking of setting up doubles to get some instruction from someone who is qualified.

 

[Storker]

I agree about the isolation manifold issue; if you have a doubles set with an isolation manifold you should know that it's supposed to be open, both during filling and diving. But that point can be made in about five minutes by a half-competent LDS worker.

My point is that there are no fundamental issues that are different between singles and doubles. It's all about capacity, NDLs, min gas and redundant gas if you dive beyond NDLs. And diving beyond NDLs may just as well happen with a big-a$$ single as with a moderate-sized doubles set, and in that case you're worse off carrying a big-a$$ single than if you carry a moderate-sized doubles set with an isolation manifold. Unless, of course, you're also slinging a decently sized pony.

 

[victorzamora]

How is my clubmate's 232 bar D7 (~110 cuF) irresponsible while my other clubmate's 300 bar 12 (~115 cuF) is responsible? How is my clubmate's 232 bar D8.5 (~135 cuF) irresponsible while the 300 bar 15 (~145 cuF) that I just sold (since I don't need that amount of gas and it was a b!itch to haul and stow) is responsible?

Tanks aren't behavior. Doubles doesn't necessarily mean lots&lots of gas. And if you dive dry in cold water, you just might need more than an Al80 to last you an hour's worth of responsible no-deco diving, within both NDLs and min gas. I use some 25-30% more gas when I dive my trilam suit in my home waters than if I dive a 5 mil wetsuit in warm waters, and my 300 bar 10 (~100 cuF) holds just enough to approach no-stop limits if I don't have a bad air day.

Storker, I know that you're all up at arms about people calling doubles "tech gear"....but that's not what's happening here. Your clubmates, I hope, had dive buddies competent enough to show them the ropes. I'm sure that before they strapped some doubles to the back of their jacket BCDs with bungee cords and duct tape that they knew a little bit about the setup. The OP is asking about SPGs on doubles, indicating little knowledge of the subject. Training doesn't have to be formal, but it's very prudent for Tobin to suggest seeking help. I'm sure all of your buddies had help.

---------- Post added June 17th, 2015 at 02:25 PM ----------

My point is that there are no fundamental issues that are different between singles and doubles. It's all about capacity, NDLs, min gas and redundant gas if you dive beyond NDLs. And diving beyond NDLs may just as well happen with a big-a$$ single as with a moderate-sized doubles set, and in that case you're worse off carrying a big-a$$ single than if you carry a moderate-sized doubles set with an isolation manifold. Unless, of course, you're also slinging a decently sized pony.

No, but setup and gear configuration and diving tricks/tips and the multiple knobs do make them different than one big tank. All divers should know how to use one big tank. Not all divers are taught the proper way to dive doubles.

 

[PfcAJ]

Wonderful! Exactly the manifold of my dreams. Thanks again. Are 5.25 double bands available, able to fit on a BCD or a simple plate with wings? I have my old set mounted on a vintage back plate, but something new and sturdier that would allow the use of buoyancy control might be preferable.

I've tried side mounts, but because I try to stay as sleek and as close to the feeling of free diving as possible, they were not for me.

At 73, I'm getting close to aging out of diving, one way or another. I can't handle heavy tanks as effortlessly as I once did without pulling some damned muscle or another. I'd like to try twin aluminum 40s over the coming decade or so that I might be able to squeeze in.

https://www.divegearexpress.com/dgx-premium-doubles-bands-set-w-bolts

5.5'', might work?

 

[Storker]

setup and gear configuration and diving tricks/tips and the multiple knobs do make them different than one big tank.

AFAIK, the only fundamental difference between my single tank setup (BP/W, LH/BO) and my clubmates' doubles setup is one first stage reg and two valves (one tank valve and one manifold valve).

All divers should know how to use one big tank. Not all divers are taught the proper way to dive doubles.

Again, what with "the proper way to dive doubles" is different from "the proper way to dive a single tank"? Except remembering to keep the isolation manifold valve open, that is?

 

[Adobo]

I agree about the isolation manifold issue; if you have a doubles set with an isolation manifold you should know that it's supposed to be open, both during filling and diving. But that point can be made in about five minutes by a half-competent LDS worker.

My point is that there are no fundamental issues that are different between singles and doubles. It's all about capacity, NDLs, min gas and redundant gas if you dive beyond NDLs. And diving beyond NDLs may just as well happen with a big-a$$ single as with a moderate-sized doubles set, and in that case you're worse off carrying a big-a$$ single than if you carry a moderate-sized doubles set with an isolation manifold. Unless, of course, you're also slinging a decently sized pony.

Most things about diving, once you understand them deeply, seem like they could be explained by a "half-competent" LDS worker. But reality is, its not that simple to the person who is new to it. I mean, to go from single tank diving to diving doubles with an isolation manifold, you are at least talking about gear changes such as:

- New wing - how do you select the proper size for your doubles?
- another first stage
- configuration changes to how the regs are set up (at a minimum, there are likely changes in hose lengths for the SPG and the back up reg).

The last point assumes that the diver is already familiar with having a backup reg on a necklace and having an SPG by itself as opposed to being part of a console. What happens if diver is only familiar with the traditional recreational regulator configuration with a console that has the SPG, dive computer and compass?

Another concept that would need to be covered is how to get weighting down properly for doubles. And how the different ways one can add ballast when diving doubles.

There are a lot of things going on that maybe "simple" to you but are not necessarily so to someone who is new.