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Post by snark3 on Nov 24, 2019 10:29:13 GMT -8
Yesterday I had an interesting situation. I was taking some tanks to be filled and checked the pressure before I put them in the truck. One of my steel NED 72's had only 200 psi. I know I didn't drain the tank that low so I figured maybe the valve is leaking. I have a known good USD K valve so I figured I'll put that in. I put a new Oring on the USD valve, pulled the Healthways ( I think) valve from the tank. When I tried to put the USD valve in it went in about 2 turns that's it, almost like it was crossed. I tried several more times and 2 other USD valves all with the same result. The original valve went back with no issue. I put the valves together thread to thread and they matched. Anybody got any thoughts on why the USD valves wouldn't go in?
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Post by nikeajax on Nov 24, 2019 10:57:59 GMT -8
Skip, the only thing I can think of is that the tank has a slightly different pitch, and since the valves are brass, the one you pulled is mated to the tank... Just a thought!
JB
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Post by cnotthoff on Nov 24, 2019 11:07:08 GMT -8
I've run into this a few times with new tanks. It's been an issue with the valve each time. Minor dings in the threads can cause this problem. Good thing you're smart enough not to apply a six-foot breaker bar to screws that sucker in. Experiment with a few other valves to confirm that the problem lies with the valve threads.
Time to rebuild that Healthways valve so there's no leak.
Good Dives, Charlie
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Post by nikeajax on Nov 24, 2019 11:30:28 GMT -8
Skip, I think you may be able to use something to straighten the threads...
JB
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Post by snark3 on Nov 24, 2019 12:32:02 GMT -8
Charlie- I tried 3 different valves, all USD, and had the same result with all 3. But I think you're right its time to rebuild that valve. I think its ready, the valve is 45 years old and never been touched.
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Post by vance on Nov 24, 2019 12:47:09 GMT -8
Skip, Are they 3/4" or 1/2" valves? Be sure you're not trying to mix straight and NPT threads.
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Post by SeaRat on Nov 24, 2019 13:08:31 GMT -8
Any possibility that the Healthways valve and tank are Metric?
John
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Post by snark3 on Nov 24, 2019 13:48:19 GMT -8
These are 3/4 Oring valves I believe.
John- I suppose the Healthways could be metric.
I put the original valve back in but put this out here to get different thoughts on what the issue could be.
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Post by vance on Nov 24, 2019 14:40:03 GMT -8
I've only seen 1/2" npt, 1/2" straight, and 3/4" straight valves/tanks. I think the steel 38s with bushings are 3/4" npt reduced to 1/2" npt. But are there 3/4" npt valves?
Skip's would be straight if it has an o-ring.
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Post by herman on Nov 25, 2019 4:07:11 GMT -8
Do the tanks have an ICC or DOT stamp on them? If so, they are not metric (at least not a vintage tank)....and if they don't they should not be accepted for hydro in the US. I ran across some Faber tanks from the 70's that exhibited the same thing, I was working a project for a friend in the Dutch Caribbean which is why he had them. The threads looked like standard 3/4 threads but turned out they were British Whitworth pipe thread (BSPS). Almost the same size, thread pitch was the same but the thread angle was 55 deg instead of the 60 which is used in imperial and metric threads. Its not likely this is the case but I have seen it. Try putting the healthways valve in a known good tank. If it's BSPS, it will go in but be really sloppy- excessively wiggles side to side when theaded in most of the way. Absent of that and considering you have tried several valves, I would be looking for some defect in the tank threads.
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Post by snark3 on Nov 25, 2019 8:06:10 GMT -8
Herman-this tank does have a DOT stamp on it. I bought this tank new in 1974 locally. Phil= I believe the tank and all the valves I tried were 3/4 - 14 strait with an O-ring seal.
I think Herman may have hit it with the defect in the tank threads. Could the machining tolerances be off enough for this to happen?
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Post by herman on Nov 25, 2019 13:19:15 GMT -8
Machining tolerances could be an issue. If the tank threads are a bit undersized it can do just as you are seeing. I cut custom threads all the time on the lathe and the test is to try a nut or whatever you are threading to. It only takes a few thousands of a inch to go from won't work to works fine. When you are very close, the nut will thread on 2 or 3 turns then stop, usually a second pass at the exact same depth will finish the job by removing a tiny bit more metal. For a reference a sheet of copy paper is between 3 and 4 housands of an inch thick, that's not much. I doubt that is the issue but it is possible. I would carefully inspect the first few threads in the tank. A slight ding in them is enough to keep a close tolerance valve from working but if the HW is a bit worn or oversized (deeper threads) or it has been forced in which cut it's threads a bit deeper/wider- it is brass after all, it may fit but the undamaged valves would not. Check the threads of the HW valve carefully, is the chrome gone or damaged on the threads? Odds are it will be on one side but not the other if its a ding in the tank threads. A piece of crap lodged in the threads can also cause the same thing. If the threads are damaged, running a tap through them would likely fix the issue....if it's cost effective or not to buy one is a different discussion. A hydro shop or maybe a dive shop might have one you could use.
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Post by snark3 on Nov 25, 2019 14:04:48 GMT -8
Thanks Herman. Prior to posting this I put the Healthways valve back in and had the tank filled. I'm going to keep an eye on it and see if it leaks down. If it does it my be time to retire this tank, I have several other 72's that can be brought out of retirement. This one does have some sentimental value as it was my first tank. Maybe I can find a source for a burst disc for a Nemrod valve. Diving a Snark III with a Nemrod tank and valve might be cool
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