Doubles with a single first stage

[aquaregia]

Although I'm a fairly new diver I've been considering doubles at some point in the future. I just got an old pair of steel tanks and recently found for sale some bands and an old manifold for steel 72s. The manifold apparently has a single K-valve outlet, so I'd only be able to dive these in "one big tank" mode. It seems like that would be a valuable intro so I could get used to doubles, and as my regulators are still A-clamps I wouldn't have to worry about the DIN conversion yet. On the other hand, it does seem like hardware that I'd outgrow somewhat quickly.

I'm sort of curious if people think that this would be a worthwhile transition, or sort of a waste of money. I'm sort of guessing, but I imagine this would be more reasonable than playing with independent doubles?

 

[Gilldiver]

If the tanks are in hydro, offer up to 75 each, if out of hydro I would not pay more then 50 unless I had an understanding that the money is refunded if they don't pass vis and hydro. There are plenty of threads on vintage 72's on what to look for and look out for.

If the bands are vintage bands, say $25, and the manifold maybe 50-75.
Keep an eye on ebay or go over the one of the vintage diving boards and see if anyone has a 2 post sherwood manifold for sale like this one:

The above manifold should run anywhere from 50-100 and it will work with your bands.
The alternative is to get a newer manifold whith the posts over each tank and new bands for the 6.9" tanks and modern spacing.

Twin 72's make a very sweet set of doubles with great boyancy and I use mine for most dives in the 80-120/130 foot range. Deeper then that and I will go to a bigger set, but I am a Hoover for air.

 

[halocline]

As long as the bands and manifold are compatible widths, you should be fine. As Pete said, double 72s are terrific and very popular among the vintage crowd. I have a set, but I use a modern isolation manifold and two regs.

You'd want the manifold to be a "center outlet" type for a single reg; I've only seen those in j-valves, but I imagine there are K-valve ones as well. If you have a backplate and an appropriate wing, you'll find using twin 72s an easy transition from single tank. Be prepared for some adjustment with trim and buoyancy.

If you put the set together and eventually want to move on to larger doubles with a modern manifold, you'll have no problem selling the vintage set to a doublehose diver.

As I'm sure you're aware, using doubles means you have more air and therefore more possibility to run into deco situations. In this case, with a single outlet manifold, you'd just be using your normal reg set up, so there's nothing new there. You might want to make sure you can easily swim the set to the surface with no air in the wing if you're using a wetsuit. LP72s are neutral when empty so the issues with steel doubles and redundant buoyancy are not nearly as problematic. Worst case, I imagine the set is less than 15lbs negative at the beginning of a dive; that's bands, manifold, gas, reg, and backplate.

 

[DaleC]

Curious why you think this would be more reasonable than playing with independant doubles? (BTW, I don't play with my ID's; I dive them)

The ony difference between ID's and MD's is the isolator valve in the middle. With ID's you can still practice reaching the valves and routing the regs/hoses as you would with MD's. For practice purposes, ID's would simulate MD diving more than a single outlet manifold would.

 

[aquaregia]

Sorry, I used "playing" to indicate that I didn't have an immediate need for either the gas or redundancy in a set of doubles, but rather was trying to get used to the weight and trim in baby steps. I assumed that ID wouldn't really constitute baby steps because I couldn't dive them as a single big tank due to the need to breathe the tanks down together. I certainly didn't mean to say anything disparaging about independents.

It hadn't occurred to me that the bands for 72s would be spaced differently to bands spaced for more modern manifolds. I'd definitely like to avoid ending up with a garage full of junk I can't use. Decisions decisions...

 

[DaleC]

No problem, I seem to be in a feisty mood today for some reason. I think the spacing may be the same for the 72's if you are switching from a single outlet manifold to a isolating manifold (good question for the vintage sub forum though). If you are going to use different tanks down the road however (Al 80's, ST 100's, St 130's etc...) the bands will be different. Double ST72's/single outlet manifold would make a nice rig though you do lose all the benefits of redundancy other forms of doubles provide and I believe Captain on the board here says he likes to use them rather than one big tank because they trim out nicer.

 

[Paladin]

My current double 72 set is actually two singles with K valves connected by a center tap cheater bar. This setup is the most practical for me because I can either dive doubles with my double hose Aqua-Master or I can separate them and dive them as singles. The best of both worlds. I have a USD double manifold here that needs a good internal cleaning. I just haven't gotten around to it yet.

 

[Thalassamania]

A single outlet setup is not a good approach, I'd learn to dive them as independent doubles, a approach that a few diving experts see as equal or superior to all others.

 

[Graeme Tolton]

There is really no safety benefit to having a single outlet manifold. With independant doubles, you get the benefit of a malfunction never compromising all of your gas. However, you will need a second SPG and train yourself to keep track of what you have left in what tank. steel 72's are very good tanks. Many of them are still around from the 50's. If the price is fair, my suggestion would be to buy them and buy modern manifold and bands. That way you get the benefit of being able to turn individual regulators off, while still having access to your entire gas supply. The single outlet may be in perfect condition, but if you are looking to do any courses (tech), you may get some harsh criticism from from potential instructors.

 

[binobanana]

A single outlet setup is not a good approach, I'd learn to dive them as independent doubles, a approach that a few diving experts see as equal or superior to all others.

Absolutely right! You want a new manifold (isolatet), if you think about double you think about extending time or go deeper. This goes into teck sooner or later, you want to be able to hook up 2 regulators! if you set up a double, do it right from the beginning!
Also make sure, your BCD supports a double rig!
A new manifold runs 300 bugs! It is worth the money!

And you can convert every regulator to Din, that would be your first step!


I just don't see the point using those for recreational diving?
I dive a single 113 LP Tank and i pump it up to almost 3000! it weights less, its smaller than a double and i did not have to work on my BCD!

But hey! If it makes happy!
Stay safe!