What's your favorite set of doubles?

[stuartv]

Sherwood, Genesis: is there even a difference?

(Why do I want the 120's back? I managed to find a set of Dive Rite (Thermo?) 7/8" modular valves that accept a standard isolater that I can use standard tank bands with!)

I may have misspoken about the 2 different kinds of manifolds I have. One kind has plugs that screw into the valves, if you want to use them on single tanks. The other kind would need a cap, instead of a plug, in order to use the valves on single tanks. I have only one of the manifolds that uses the plugs, and I do have the plugs that go with it.

Also all mine are the older 3500 psi kind, with the skinny necks. And right now, I can't remember whether that means they are 7/8" or 3/4". But, they are whichever one requires the older, harder-to-find valves. So, not sure if the DR valves you found would work or not. But, I'm guessing from the context that they would.

In which case, do you want to sell me those valves? Or tell me where I can get 2 pair for myself?

 

[tmassey]

Skinny valve = 7/8" (yes, the bigger number: they're different thread standards....) The ones that allow plugs are the modern (I won't say *better*) style: they have double or triple o-rings along the axis. The others are a face-seal with only a single o-ring, but it's a much stronger type of connection: much less opportunity for off-axis deformation, for example. If they're tight. And installed correctly: there's much less margin for slop. But the face-sealed manifolds were built on an 8" center (actually, 8 1/8" or 207mm) and the modern ones are built on 8.5" center (215mm). That was necessary to accommodate 8" tanks and still have room for bolts between the tanks.

I've heard they made decent bands for 207mm for like 5 minutes 15 years ago, but I've never seen them. The only ones I've seen are thin 1/16" sheet metal (or thinner?) 1.5" wide with spot-welds to hold the bands together, not the modern full-welded bands that are 2" or 2.5" wide, 1/8" thick and with a solid metal spacer between the tanks.

Do the thin bands and narrow and slanted manifolds work? Certainly, 100%. And so do my 1980's Sherwood regulators. But I'm ready to move on.

You can have my valves over my cold, dead body. It sounds like you have a set of them (or functional equivalents, anyway) already. Without the valves, I can't use standard bands! And I so want to use standard bands... And where to get them? Good luck. All I can say is look around... But there's 10 of the Genesis manifolds for every 1 of the modern style (and there aren't that many Genesis manifolds in the first place...)

 

[tmassey]

I also very much prefer the double 12 Liter, 232 Bar with a concave bottom.
It rides perfectly on my back and keeps me in good trim.

Those are non-USA tanks. The closest we have are LP85's or HP100's. I don't know the exact specs of the tanks you're describing, but they're likely to be smack dab right in between the two. LP85's are slightly longer and slightly more narrow than HP100, are slightly lighter and when filled to the same pressure hold slightly more gas. Given that European and Australian tanks tend to be a little lighter than American tanks (certainly for the same pressure), are rated for 3300 PSI *AND* have the concave bottom, they sound like the ideal SCUBA tank!

Pity Americans can't actually use them...

 

[johnohuk]

My favourite twins are Euro 8.5Ltr round bottomed, coupled with a Halycon evolve 40 were a joy to trim/dive, only issue, it never had enough gas for a two dive boat trip. Upgraded to the twin Euro 12ltr concave cylinders, loads of air but nearly crippled me coming up a ladder... so split and side mount them now, marginally easier

 

[tmassey]

Looking at getting into doubles as the next logical step in my Scuba journey. The challenge is that my wife and I need to both be able to use the bottles for single tank diving (don't want to buy 4 bottles!).

Taking doubles apart is non-trivial. The tanks need to be drained and then allowed to warm, then disassembled, then filled, and if you don't have a compressor the fill people may not be thrilled with a completely empty tank. (That warming step is vital: don't do it and you risk corrosion of the inside, which is why VIP's were invented in the first place.) Putting them together is harder: same drain and warm, and assembling the doubles is annoyingly fiddly.

Would two 12L Faber Steel cylinders (we use the metric system) be a good decision or should we be looking at two 10L bottles instead? I am also not sure about Steel versus Aluminium for doubles.

Except for rental or for weird reasons, doubles are almost always steel. Better capacity, more rugged, less floaty. A single aluminum is pretty floaty. Two is annoyingly so. Yes, you can fix this with a tail weight, but I'd rather have functional weight: better tanks.

10L vs 12L: the biggest factor is tank length vs. your height. We had a discussion about HP120's, and how you have to be at least 6' tall to use them properly. (Conversion to metric lengths are an exercise for the reader: Google is your friend.) The same is true of 10L vs 12L (assuming same tank diameter). I find 10L tanks unpleasantly short given my height and long torso. My 5'4" daughter trims out nicely in them.

Also, I am not sure what LP85 LP80 etc means haha. Assume LP = Low Pressure and HP = High pressure? HP being 3500psi? How does 80 etc compare to liters?

They don't, really. Yes HP is High Pressures (usually 3442 or 3500 PSI, roughly 240 Bar), and LP is Low Pressures (usually 2640 PSI, or 180 Bar). So, an HP80 and a LP80 have the same number of gas molecules in them, but one is a tank with bigger physical dimensions (the LP) because the molecules aren't as packed together (lower pressure). You might want to look at a reference that has both water volume (European way of measuring tanks) and gas capacity (American way of measuring tanks) to get a feel for the differences. (Strangely enough, I just made such a chart: https://www.scubaboard.com/communit...ifications-list-in-pdf-and-spreadsheet.572616 )

 

[Steve_C]

I assume that most of this discussion is cave or shore oriented. I have been on boats where the limit for rec dives is 2 tanks but you are doing 2 dives. A pair of 50s would not work well for that scenario for most males.

 

[seeker242]

I assume that most of this discussion is cave or shore oriented. I have been on boats where the limit for rec dives is 2 tanks but you are doing 2 dives. A pair of 50s would not work well for that scenario for most males.

Buddy brings 2 pairs of 50s and swaps them out.

 

[Steve_C]

Buddy brings 2 pairs of 50s and swaps them out.

So your buddy is going to pay $100+ to ride out on the boat with you, and sit on the boat for several hours reading the paper, so you can dive his/her tanks on dive 2? Pretty good buddy.

 

[seeker242]

So your buddy is going to pay $100+ to ride out on the boat with you, and sit on the boat for several hours reading the paper, so you can dive his/her tanks on dive 2? Pretty good buddy.

Huh? I bring my 2 tanks. And instead of him bringing 2 tanks like me, he brings 4, AKA "2 sets of 50s".

 

[-JD-]

I may have misspoken about the 2 different kinds of manifolds I have. One kind has plugs that screw into the valves, if you want to use them on single tanks. The other kind would need a cap, instead of a plug, in order to use the valves on single tanks. I have only one of the manifolds that uses the plugs, and I do have the plugs that go with it.

Also all mine are the older 3500 psi kind, with the skinny necks. And right now, I can't remember whether that means they are 7/8" or 3/4". But, they are whichever one requires the older, harder-to-find valves. So, not sure if the DR valves you found would work or not. But, I'm guessing from the context that they would.

In which case, do you want to sell me those valves? Or tell me where I can get 2 pair for myself?

Skinny valve = 7/8" (yes, the bigger number: they're different thread standards....) The ones that allow plugs are the modern (I won't say *better*) style: they have double or triple o-rings along the axis. The others are a face-seal with only a single o-ring, but it's a much stronger type of connection: much less opportunity for off-axis deformation, for example. If they're tight. And installed correctly: there's much less margin for slop. But the face-sealed manifolds were built on an 8" center (actually, 8 1/8" or 207mm) and the modern ones are built on 8.5" center (215mm). That was necessary to accommodate 8" tanks and still have room for bolts between the tanks.

I've heard they made decent bands for 207mm for like 5 minutes 15 years ago, but I've never seen them. The only ones I've seen are thin 1/16" sheet metal (or thinner?) 1.5" wide with spot-welds to hold the bands together, not the modern full-welded bands that are 2" or 2.5" wide, 1/8" thick and with a solid metal spacer between the tanks.

Do the thin bands and narrow and slanted manifolds work? Certainly, 100%. And so do my 1980's Sherwood regulators. But I'm ready to move on.

You can have my valves over my cold, dead body. It sounds like you have a set of them (or functional equivalents, anyway) already. Without the valves, I can't use standard bands! And I so want to use standard bands... And where to get them? Good luck. All I can say is look around... But there's 10 of the Genesis manifolds for every 1 of the modern style (and there aren't that many Genesis manifolds in the first place...)

All PST HP-3500s for me: (6) 100s and (4) 120s - all singles ATM.

I have a Thermo manifold set (I believe this: XS Scuba Thermo DIN Manifold 7/8-UNF 3500psi - says they are available if you are interested) that I picked up on here (minty "used") just in case I want to double some of my PST 3500s in the future. It is a 2-oring arrangement with the seal-shaft notably smaller than the fine-threaded section. It isn't assembled, but lining it up, it sure looks like it should be 8.5" center to center - a call or email to XS/Thermo or Diver's Supply would probably deliver the official design-spacing answer.

One pair of my 100's came split with an isolator crossbar and bands on the side. They are slant-back with a "Made in France" cast-in so I'm guessing Sherwood/Genesis. Eyeballing it with the manifold, it look like it would end up at 8" CC almost fully engaged. The OMS bands that came with it look like 8.5" CC, though. Possible the guy mixed up the bands ... Or maybe those Genesis manifolds have a wider adjustment range? The Genesis has 7/8" of exposed thread (after the nut) on the isolator/crossbar vs. 1/2" on the Thermo, and the seal-shaft is similarly longer. I think you could probably get an easy +1/4" on each side and get to 8.5" CC with greater thread engagement than the Thermo. Unfortunately the tanks are full, so I can't easily pull the plugs to check the seating depth.

I have a couple of odd-duck 7/8" 232Bar style manifolds that I picked up from John @ NESS. They also seem to be 8.5" CC. I'll be splitting them and putting them on some of my 3500s once I get the plugs from John and the tanks go in for VIP. I'll then be able to throw some DIN->Yoke converters in there if I need to loan out a tank for someone with yoke regs.

FYI this is for informational purposes only. I'm not looking to sell any of my manifolds ATM.

Also, FYI: 2 of my 120's I recently purchased from John in Oct/Nov before he got to process them (they need to go back to him for hydro/tumble/clean/VIP but I wanted my timeout to occur during off-season). At the time, he had 2 additional 120s waiting for processing. If you are looking for a set, it is possible (probable) they are either waiting for, or in-process and may be coming available. Might be worth a call if you are looking ...