Valve help: converting old LP72s to modern doubles

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Bowers

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Unfortunately those are the 1/2” npt... i ran into this problem a while back and could not find a modern valve for it. You will find search results saying you can use tapered thread valves with pipe tape but thats for a European or something small thread (or so i gather), not for what you have. You’re best bet is to either use them as singles with current valves or resell them and buy some tanks with 3/4” threads.
When you do find tanks that will work for doubles, the 6.9” bands can be hard to find. I have used 7.25” bands tightened down a little extra on 72’s multiple times with no problem.
Best of luck!
 

Luis H

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Like @James79 said, those use a thread type that was only used on Scuba tanks for a short while in the 60's (used mostly by Sportways, but White Stag also used it for a little while).

There are no modern Scuba valves, either double or single tank valves made for it. As mentioned (again by @James79 you could maybe get a standard 3/4" NPS valved machine down, but I don't think it is worth it.

Finding steel 72 with the standard 3/4" NPS neck is not hard.


An interesting observation is that some fire fighting SCBA cylinders use that size neck. The SCBA valves would fit in it, but they are only for single cylinders and most have built in gauge that is not intended to go underwater. I have seen (a couple of times) home made manifolds that someone used two SCBA valves and connected them with the center piece of a Sherwood manifold. The Sherwood vintage manifold used the same CGA connection (for air) used for the SCBA regulator.

Actually in one of the cases they didn't use a Sherwood center piece, they just used CGA fittings with a high pressure T and a they probably made a yoke outlet.
 

Scared Silly

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Thank you very much for the reply. This gives me hope. :)

The description on the DGX 7.25" bands says they fit 7" and 6.9":

The 7.25-inch bands and bolts also fit the 7.0-inch diameter LP85's and the 6.9-inch diameter AL72's, with the bolt height adjustment depending on the depth of the "V" in the backplate. The adjustable height bolts in the 7.25 bands and bolts kit will work fine on these slightly narrower cylinders.

So, I'm keeping my fingers crossed on those too.

While DGX usually has some good info, using 7.25" bands on 6.9"/7" cylinders goes against the conventional wisdom. Especially given that one can find 7.00" Stainless Steel Cylinder Bands easily.
 

Ghost95

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A while back I was trying to do the same thing. I contacted XS scuba about a run of valves with 1/2" NPS threads. I believe they had a minimum run of 30 and they were going to be like $75 each.

If the run was like 10 I would have done it and sold them out over time but between price and the minimum order I couldn't justify it.

I posted on here to see if people would be onboard for the order but I got no interest. Good luck.
 

herman

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Unfortunately those are the 1/2” npt... i ran into this problem a while back and could not find a modern valve for it. You will find search results saying you can use tapered thread valves with pipe tape but thats for a European or something small thread (or so i gather), not for what you have. You’re best bet is to either use them as singles with current valves or resell them and buy some tanks with 3/4” threads.
When you do find tanks that will work for doubles, the 6.9” bands can be hard to find. I have used 7.25” bands tightened down a little extra on 72’s multiple times with no problem.
Best of luck!

Those are NPS not NPT. While earlier tanks were NPT (those do use pipe tape) the ones shown are actually 1/2 NPS, note the oring at the top of them. They are not too common but Healthway and Sportways (like these) offered them for a while. I have a couple of them.
 

Eric Sedletzky

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Thank you very much for the reply. This gives me hope. :)

The description on the DGX 7.25" bands says they fit 7" and 6.9":

The 7.25-inch bands and bolts also fit the 7.0-inch diameter LP85's and the 6.9-inch diameter AL72's, with the bolt height adjustment depending on the depth of the "V" in the backplate. The adjustable height bolts in the 7.25 bands and bolts kit will work fine on these slightly narrower cylinders.

So, I'm keeping my fingers crossed on those too.
I had a set of 72’s as doubles in the past. I used regular 7-1/4” OMS bands and an OMS butt connected style manifold with an isolator valve. The way it works is the bands just squeeze in more to fit the smaller diameter tanks so the two flat parts where the 5/16” rod goes through are just a bit closer together, which when drawn in also pushes out the center of the 6.9” tanks to equal what the 7-1/4 tanks would be on center.
The way I figured this out was I ordered a set of bands/manifold for 72’s from LP and they fit fine.
Years later I broke down the 72’s and banded up a set of 7-1/4’s with the same bands and manifold and it worked perfect.
 

Bowers

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Those are NPS not NPT. While earlier tanks were NPT (those do use pipe tape) the ones shown are actually 1/2 NPS, note the oring at the top of them. They are not too common but Healthway and Sportways (like these) offered them for a while. I have a couple of them.
Good catch, i knew better but typed wrong. Thank you for the clarification
 
https://www.shearwater.com/products/peregrine/

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