Bushed tanks@3000 psi

[nemrod]

Has anyone used an aluminum 3000 psi tank on a bushed pipe thread valve using a bushing adapter? The valve is indicated as 2250 service but looks strong enough to run 3,000 psi which is really on 500 psi over the plus pressure these valves were used at? Any thoughts on this? What would be the max pressure you would use a bushed valve at in good condition with clean threads?

James

[Deleted]

James

If you're talking about the bushing used in welding tanks as well as the early scuba tanks, they are rated at 4000 psi.

Michael

[SeaRat]

James,

The 1/2 inch pipe valves were 2250 psi rated, and could go to 2475 psi. If they are the newer ones, with a copper disk, then a new disk for 3000 psi could be used. But if they are the older valves, with a molded lead burst piece, then you cannot go to 3000 psi. I have a couple of those old valves, and I'll look to see what burst mechanism they have. It could be that the older style could be replaced with a newer one too. Maybe someone could comment on that.

John

[duckbill]

Hey Nemrod, in case you miss my reply over at Vintage Double Hose (am I allowed to say that here?):
Hi Nemrod,
I wouldn't do it. If you do, make sure you get stainless steel high pressure-rated bushings. They are hard to find around here even in pipe-to-pipe. I've never heard of them being available in straight thread/o-ring to pipe thread.
I've been told by a local hydro guy that bushings are actually legal for a dive shop to fill IF the bushing is, as mentioned, stainless and stamped as rated for the working pressure. He said he could get some to replace my 'illegal' bushings in a set of old 1800 psi 1942 Navy twin 38s I have. Maybe I'll have it done some day, but only my local shop would fill it for me. Probably about 99.5% of shops assume that ANY bushing is illegal.
I hope you have your own compressor!

And, I might as well add here that the vast majority of hydro-testers probably think that all bushings are illegal too, and won't hydro a tank having one. I've even heard that they are required to confiscate the bushing, but I'm not too sure about the legality of that one as it pertains to private property. Of course, with a standard alumunum tank, you could simply remove the bushing for testing. They would remove it anyway.

[Captain]

Do not try to use a 3/4" tapered pipe thread bushing in an aluminum tank. As you screw the bushing in the taper will try to expand the neck of the tank putting stress on it. I have made stainless bushing by using a 1/2" by 1" bushing and turning the 1" down to 3/4" straight thread. You can get the 3/4 X 1 SS bushing from McMaster-Carr and any machine shop would be able to turn them down to 3/4" straight thread.

[Ron Hearn]

Hi James

That valve may very well look that it could handle 3000 Psi pressure, but having that valve blow off is not a laughing matter, a safety plug is a must if your going to start increasing pressure on that valve over the manufactures rating. I use brass bushings on my Nemrod steel triple set rated at 2250 and they work fine because I stay with in the limits. Be carefull.


Ron

[Deleted]

I'm not sure why a hydro shop would state that only stainless steel bushings are the only legal type allowed in tanks today. Several welding shops I have visited, searching for two 3/4 to 1/2 reducers for my second set of newly aquired 38's, have stated that the high pressure brass bushing sold for welding tanks come in two ratings, 400 psi and 4000 psi. And those are all that these particular shops have used. But the 4000 psi rated ones are hard to find. And needless to say, 400 psi rated is useless for diving purposes.
They have made no mention of stainless steel...maybe because those type are even harder to locate....anyway, stainless or brass, used in an aluminum tank will require either teflon tape around the threads or have the bushing chromed, since they are different metals and electroliss (sp) of the respective metal crystals will take place and eventually weld the bushing to the aluminum.


I have one set of Twin 45's (rated at 2250) I don't think I'd push that manifold to 3000 psi even tho it looks about the same as a 3000 psi one. From past experience, the interworkings might hold up for a while if the seat is a modern one.....if not, it'll go south much quicker over time like one of my 1/2 valves when it was over filled to 3500 psi on a dive boat last year.

I might note however, my wife uses 50 cuft aluminum's (she's a little lady) that once were twins with a cross manifold that is removable.......the thickness of that manifold is less than the thickness of my manifold on my twin 45's. Go figure..................

[nemrod]

"Do not try to use a 3/4" tapered pipe thread bushing in an aluminum tank. As you screw the bushing in the taper will try to expand the neck of the tank putting stress on it. I have made stainless bushing by using a 1/2" by 1" bushing and turning the 1" down to 3/4" straight thread. You can get the 3/4 X 1 SS bushing from McMaster-Carr and any machine shop would be able to turn them down to 3/4" straight thread. "

Tom, what I want to do is adapt a half inch pipe thread valve to a modern 3/4 straight thread tank. I too was concerned that put the pipe threa .5 inch into the adapter might "swell" the adapter and place stress on the neck. Is this what you are saying or are you telling me not to try and put a 3/4 pipe into a 3/4 straight? Obviously the later would be very bad, the former, I dunno.
I wish I could find LP steel tanks in small sizes.

Stainless bushings in aluminum should be OK since aluminum tanks are 6061 aluminum--from a corrosion standpoint. Also, I could always run the aluminum tanks at a reduced pressure, say 2500 instead of 3000 to prevent damage to the 2250 psi valve if that is truely a concern. Obviously a steel LP tank would be best but finding such tanks in small sizes such as 50cf or smaller is probably not possible.

James

[SeaRat]

James,

There is one other option that you may not have thought of, but which we used for years in the USAF. We got 20-man life raft CO2 cylinders, which have an outside thread for the valve, and re-tapped the cylinder for a 1/2 inch interior pipe thread. I don't know whether any of these cylinders are still available, but they were ICC 2100 psi stamped cylinders, and made the nicest set of small doubles. We used them for our jump tanks. However, because the tapping was done by USAF personnel, and there was no quality assurance, it was found in the 1980s that some of these cylinders had threads that had broken. So the USAF discontinued using them. I had a set made, which I also had destroyed after the USAF got rid of theirs. But it was so nice a set...

Here's a photo of those tanks on yours truely in about 1973, Clear Lake, Oregon (photo by Bruce Higgins).

And yes, I'm using my Trieste II with an octopus and SPG. I had K valves on the tanks, with a USD twin tank bar yolk (which I still have, along with the K valves) connecting them.

John

[Captain]

Nemrod, I made two stainless steel bushings to go from an old USD 1/2" double manifold to 3/4" straight thread tanks using the 1/2" to 1" bushing turned down to 3/4" straight thread. I don't really need them any more if you want them I will send them to you.

[Linda]

duckbill said:

Hey Nemrod, in case you miss my reply over at Vintage Double Hose (am I allowed to say that here?)

Of course you can... This is Vintage Scuba Supply, not Vintage Nazi Supply.

[Deleted]

James

small twins come up quite often on ebay, I have two sets from there.........the 45's I spoke of earlier in this thread and a second set of 38's I won last month.......there some nasty looking ones also occasionally on ebay but if the valve is on the tank chances are it's clean inside..galvanize exposed to several years of sea water diving get a ugly color.....but there is a risk of wining a bad one too...........

1800 psi on most of them......but that pressure is nominal to steel and with proper care will last longer than you or I. Even the nasty ones will clean up with a good coat of paint if they're galvanized, or like my first set I bought from a dive shop 20 years ago, scrap the vinyl off and nickel plate them............painted after than......second set of 38's are vinyl also, outside as well as inside.......not a problem....these were pristine..however... the inside will tumble clean if rust spots were there and outside can be touched up or refinished.........

Michael

[nemrod]

"Hey Nemrod, in case you miss my reply over at Vintage Double Hose (am I allowed to say that here?)"

Probably side traking my own thread but I generally post the same thread on both boards because some people do not cross over and also because I like both forums and the people on both and feel I should not play favorites or sometimes I put one thing on this one and next time on the other--I guess I am goofy that way. On the other hand the only thing scubaboard is good for is aggravating Techies---lol-----all in fun and good humor of course.

I do watch ebay for small twins but I keep getting out bid, lol, and of the three 72s I have bought only one could be hydroed, one has an epoxy interior coating and the other was severely pitted despite looking good on the outside so that makes the one good tank very expensive.

James

[Creed]

nemrod said:

"Hey Nemrod, in case you miss my reply over at Vintage Double Hose (am I allowed to say that here?)"

Probably side traking my own thread but I generally post the same thread on both boards because some people do not cross over and also because I like both forums and the people on both and feel I should not play favorites or sometimes I put one thing on this one and next time on the other--I guess I am goofy that way. On the other hand the only thing scubaboard is good for is aggravating Techies---lol-----all in fun and good humor of course.

I do watch ebay for small twins but I keep getting out bid, lol, and of the three 72s I have bought only one could be hydroed, one has an epoxy interior coating and the other was severely pitted despite looking good on the outside so that makes the one good tank very expensive.

James

Did you already get rid of the epoxy lined one? 'Cause I had an epoxy lined 72 hydro'd and VIP'd at Adventure Sports, and they didn't give me any problems. I know that you sometimes frequent Pro Ski & Scuba. They might not be inclined to VIP the tank, where the AS guy probably will.

[nemrod]

Neither would do anything for me. The rules have changed so they both claim. Yeah PSS was actually destroying perfectly good 72s and would not sell them to me!!!! The other shop is an OK group but they are the ones I first tried. No---I have not gotten rid of them because I hear Bryan so likes to tumble tanks that I am saving them for him just in case he gets bored one day!!!
Speaking of tumbling, my old feller, a 12 yo collie just tumbled part way down the deck stairs, I had to rescue him and then I fell the rest of the way with his 80 lbs in my arms, no, I did not let him hit the ground but now I got a good size bruise on my back---he is fine. When we were at Lake Oauchita my other old feller got a head of steam up going down the dock and he tumbled right off the end into the water followed closely by my wife--all I saw was feet and tails, getting them back up on the dock took some effort on my part. Between carrying those dogs around and my parents around while there I was a might sore, such is the state of my affairs. Good thing I am fairly durable. Nemrod