Explanation on what's required for Doubles

[ajduplessis]

Know what you want and why. Then make sure you have $$$$$$$$$$$$$$$$

 

[MKrauter]

Thanks for the article flots. Proving to be very informative.

Again, thanks for the information everyone. Just got some news today that may throw a wrench in my plans but we will see.

 

[DevonDiver]

Be sure of what? As far as I know GUE does not accept sidemount, though I've heard rumors they're trying to get something worked out.

Jarrod wrote a policy paper on sidemount and CCR in the latest GUE members mag ('Quest'). Sidemount is definitely in the future, but decisions are still to be made about implementation within the wider GUE philosophy. I suspect, from reading the article, that it'll be a specific-to-task 'tool' for confined environments/passages, and that, when used, it'll be no mixed teams; all divers in back-mount or all in sidemount.

 

[halocline]

Double AL80s are perfectly fine doubles to start with, they're very popular in warm water, and since you already have one, you'll probably spend less building them than buying even used steel doubles. My suggestion is to buy a used AL80, make sure it's the same manufacturer as the one you already have, then get either used bands/manifold, which is easy because lots of people are trying sidemount these days and breaking up their doubles, or get bands/manifold from piranha dive mfg. Their bands are excellent and the price is good. If you get a good price on the used AL80, you should be able to do the whole thing for about $300. I'd get the convertible 200 bar manifold, not the 300, but it doesn't make too much difference. You'll likely never use yoke regs on your doubles. Mine is a blue steel manifold, it's okay but I bet the thermo manifold is higher quality. I'm not sure how much difference it makes, they all more-or-less do the same thing.

Then, maybe in a couple of years when you need bigger doubles and stages for really technical dives, you can break up the AL80s and use them as stages, and, depending on the tanks you get at that point use either the bands and manifold, or just the manifold. By that time spending $100 on a new set of bands will seem like peanuts compared to the other gear you'll be buying.

Edit; I looked and saw you're in Canada, so if you're already diving with a drysuit in very cold water, you might bite the bullet and look for a set of steel doubles right away. Maybe HP100s or LP95s, those are very popular doubles. I wouldn't get anything bigger or heavier.

 

[elan]

There are two things with thermo manifolds for technical diving one is that they are tall an so move the regs up making it more difficult to trim and the other is that isolator isolates the left post (dive rites halcyons and many others isolate the right post)

AL 80 doubles are perfectly fine in canada for drysuit diving in fresh water. Its actually easy to get overweighted with tanks like hP100

 

[ajduplessis]

I dont understand the isolator comment on various brands. If you shut the isolator both sides are isolated. How did you arirve at those conclusions?? I think I am missing something somewhere.

 

[rjack321]

Nothing wrong with an OMS manifold

Yes there is. Replacement parts for Xscuba, sea-elite, dive rite, and halcyon are easily available from many different vendors. And many of them are interchangible and not exorbinately priced.

OMS parts are all unique sizes and only available for specific vendors, often for a premium price. In short, they are a pita.

---------- Post added October 11th, 2013 at 11:50 PM ----------

I dont understand the isolator comment on various brands. If you shut the isolator both sides are isolated. How did you arirve at those conclusions?? I think I am missing something somewhere.

If the isolator knob itself is leaking. You shut it. On most of the italian made manifolds (DR, halycon, sea elite) the left tank will drain and the right won't. On thermos which are japanese, the right tank will drain and the left will be closed. Undo the isolator bonnet nut on each of them and examine the holes relative to the HP seat and you'll see why. On a practical level, it doesn't matter.

 

[OkByMe]

Bear in mind that the larger diameter tanks put the L/R valve further apart, so decide on your tank diameter first, then bands, then crossover. The crossover needs to be longer to thread completely into the valves on larger tanks and of course shorter on smaller diameter tanks. If you decide to side mount later, the valves used for a manifold setup are perfect when plugged.

 

[halocline]

Bear in mind that the larger diameter tanks put the L/R valve further apart, so decide on your tank diameter first, then bands, then crossover. The crossover needs to be longer to thread completely into the valves on larger tanks and of course shorter on smaller diameter tanks.

Most bands are designed to keep a uniform center-to-center spacing regardless of tank diameter, and manifolds are designed so that they can accommodate small variances in spacing. I've never seen modern manifolds that are set for specific tank widths.

The situation with some manifolds isolating the left tank, others the right, is because the isolator valve has a single seat that seals off a single orifice, just like a regular tank valve. Once the valve is closed and the seat is screwed down on the orifice, the o-ring associated with that valve could disintegrate, the valve stem could be removed, and still no air would get past the seat. I had always assumed that the isolator valve seat covered an orifice from both tanks somehow, meaning that you could close it and not lose any air from either tank through the valve stem. I was surprised when I first took one apart to see that this is not the case; it's only a stem o-ring or crush seal that prevents leaking from one of the tanks, and closing the valve does nothing to prevent this. IMO this is a poor design and significantly decreases the redundancy potential of the isolator valve. I still think iso valves provide great redundancy due to the fact that regulator failures are MUCH more likely than an iso failure, and of course the big advantage is that with a reg failure you still get the gas in both tanks.

But if I were designing an iso manifold, I'd want to figure out a way to have a hard nylon seat seal the air from both tanks. I'd also prefer to have a simple on-off straight handle, maybe like a high quality ball valve, so that there was absolutely no way of confusing on vs off with the mechanism behind your head.

 

[MKrauter]

Thanks for all of the input everyone! Really a wealth of information here.

I don't know if this is a stupid question or not... but must the tanks be of the same manufacturer? I currently have a Catalina S80. Some of the tanks my LDS sells are Worthington and others that I have seen online are either Luxfer or Worthington... Will this matter if I double them up with my Catalina tank or should they be the same company and all that? A shop close by has offered to sell me a set of AL80 doubles for 750 which seems slightly high to me so it's something I'm considering.