Bushing Mystery

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SurfLung
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Bushing Mystery

Fri Aug 18, 2017 9:02 am

Rich's Bushing Mystery
- My buddy Rich bought a like-new steel USD 72 Tank at a garage sale. It's kind of a mystery because it is a 1964 scuba diving tank (not war surplus) that has a bushing with the 1/2" tapered thread J-Valve. Unlike other bushings, it is screwed in flush with the top of the tank. The tank neck diameter is identical to earlier USD tanks from 1961 that are threaded for the 3/4" O-Ring valves.
- At first we were thinking maybe the bushing is not a tapered thread but rather an adaptor that fits the standard 3/4" O-Ring tank necks. But when we tried to unscrew it, it is in there SOLID. It has damage from a previous (not us) use of a pipe wrench that looks like it might not have been successful... The paint looks like the bushing didn't come off. This was probably for the 5 year hydrotest that was done in 1971. And we're thinking the hydrotester just removed the valve and left the bushing in for the test?
- The insides are bare steel that is pristine except for flash rust from the hydrotest. It's a very nice tank.
- We're wondering a few of things:
1. Can we get a hydrotest with the bushing installed on the tank?
2. Is it a tapered thread bushing or a 3/4" O-Ring adaptor bushing?
3. Any suggestions for how to get it off without damaging it or the tank.?
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SurfLung
The Freedom and Simplicity of Vintage Equipment and
Vintage Diving Technique are Why I Got Back Into Diving.

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antique diver
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Re: Bushing Mystery

Fri Aug 18, 2017 11:38 am

That is a strange combination, but USD occasionally did some strange things back then, including putting bushings in NPT/NGT threaded necks. No way to tell about threads for absolutely sure without removing the bushing. That looks to be difficult without more steel to get a wrench on.

My main concern would be that maybe someone bought a hardware store plumbing variety bushing and used it to insert a different valve than came with the cylinder. It could even be a low pressure NPT bushing forced into a straight thread neck :shock:. You know I tend to err on safe side about this stuff, so I have my doubts about using it as is without learning more about that bushing.

You may have a hard time finding someone to hydro with bushing in place, but if it were to pass with it in place maybe it would be ok to use.

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captain
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Re: Bushing Mystery

Fri Aug 18, 2017 11:41 am

Good vise, 6 point 3/4 drive socket and a long cheater bar, what goes in must come out. I would remove the paint to get a good look at the joint. Look for signs that they possibly used an epoxy as sealer.
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antique diver
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Re: Bushing Mystery

Fri Aug 18, 2017 11:51 am

captain wrote:Good vise, 6 point 3/4 drive socket and a long cheater bar, what goes in must come out. I would remove the paint to get a good look at the joint. Look for signs that they possibly used an epoxy as sealer.



After removing valve from the bushing I would tighten in a 1/2" NPT plug to prevent any crushing of the bushing. Like Captain says, "6 point socket"... don't settle for 12 pt or there's too much risk of rounding off the corners.

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SurfLung
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Re: Bushing Mystery

Wed Sep 27, 2017 10:23 am

- I got the Bushing removed and it is an interesting conundrum... (that word just popped into my head):

- The bushing is a straight threaded, O-Ring Sealed Adaptor
- The threads aren't the same as standard 3/4" US Scuba Valve threads.
- They MAY be the European scuba tank thread that we see in the US sometimes.

A Possible Scenario - In 1964, US Divers discovers they have an overstock of 1/2" tapered thread J-valves and European O-ring threaded tanks. So they make up a bunch of adaptors, slap them together, and offer them to some of their big dealers as some sort of "Special Purchase". Jack the Frogman buys up some of them and sells them to some customers. Bushings were common back then so nobody saw anything wrong with this.

Why was it sealed so tight? I figure if they put the bushing into the tank first. Then installed the 1/2" tapered thread J-valve with Teflon tape and the usual torqueing force it takes to seal a 1/2" tapered thread, the bushing would be tightened right along with the valve. This may be what happened after the first 5 years when it was hydro tested. Instead, I think the valve and the bushing were intended to stay together as one body. Then they could have been removed like any other O-ring valve. When we put it back together, the valve should be installed in the bushing first, then install the bushing with its O-Ring to reasonable tightness in the tank neck. And then at the next hydro test, just unscrew the bushing and the valve as one assembly... Leave the valve installed in the bushing.

Next Stop Hydro Testing - If the tank thread is actually the European standard, we shouldn't have any trouble getting the tank hydro tested.
SurfLung
The Freedom and Simplicity of Vintage Equipment and
Vintage Diving Technique are Why I Got Back Into Diving.

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