1/2" Valve Condemned?

[duckbill]

I thought I was pretty well informed regarding the regulations concerning cylinder qualification and transportation. But, I was just thrown a curve ball this afternoon. It has to do with possible regulations regarding the valve itself.

I have several cylinders which use 1/2" taper-threaded valves.
I took a couple of those cylinders into a dive shop for the annual visual. The owner looked at them and said that one of my valves is "condemned". He said that DOT regulations state that a minimum of three threads MUST show once the valve is properly threaded into the cylinder. Since less than three threads are showing, the cylinder/valve system "as it stands" is "condemned" and will not pass visual. Furthermore, he said he couldn't fill it, even if it had a valid visual sticker.

The main question is whether anyone can definitely tell me the exact CFR this falls under, if any.Either way, has anyone else even heard of such a thing?

I could understand if there was a regulation stating the minimum number of valve threads seating in contact with the cylinder threads, but find it difficult to believe that a regulation would specify the number of threads that are NOT USED!

I also have to question the use of the word "condemned". When asked if he meant "rejected", he said, no, the cylinder/valve package "as it stands" is "condemned". This is the first I've heard of a non-DOT mandated, SCUBA industry imposed visual permitting use of the legal term "condemned".

Any thoughts or suggestions welcome (other than "get rid of those old tanks).

Thanks.

 

[Wookie]

I,ve been inspecting cylinders for quite a while (over 9 years) and have never heard of a valve causing a cylinder to be condemned. I've heard of facilities refusing to inspect the small necked cylinders because they can't get the lights in the hole, but the valve is not a part of CYLINDER inspection, in fact, when I take my cylinders for hydro and eddy current testing, the valves do not accompany the cylinders to the hydro facility. For a more final answer, check with Mark Gresham of PSI on Monday (425-398-4300), but this sounds like a inspector that just doesn't want to mess around with your old cylinders.

Frank

 

[skippy31]

I don't deal with a whole lot of taper valves, but as has been mentioned already the valve is not usually the main part of the inspection on a cylinder. There are regulations that condemn older 1/2 taper valves that have the lead slug as a burst disk, but I have never run across anything stating how many thread should or should not protrude on a taper valve. The thing with a taper valve is that if you turn it in not far enough, you have a leaky seal, and if you turn it in too far you (if you can) you strip the threads.

Playing devils advocate for a moment the only rational I can think of is that if your dealing with a brass valve in a steel tank you eventually wear away some of the brass each time you screw the valve into a steel tank. Eventually you run out of threads perhaps. But that should occur when no threads are showing...

Mat.

 

[Luis H]

I am not sure about the valve requirements, but the term "condemned" is definitely improperly used. The definition of condemned (per the CFR) is final and has no possibility of being repaired which is not the case if all you needed was to replace the valve. If that requirement was correct the proper term would be “fail” inspection and action can be taken to correct the problem.

Some of the valve requirements are not mentioned on any CFR, but instead you may find it in the Compress Gas Association (CGA) documents. CGA is not a government agency, but the CFR refers to them and therefore they are basically a requirement by the codes.

Again, I am not sure about the tapered valve requirements, but some threads showing on a tapered thread threads seems as the only indication that the valve has not bottomed out before proper engagement of the threads is accomplished.

I don’t think three threads are needed, but at least one full visible thread would indicate that enough radial tension exists before the valve bottoms out. Just think if the male tapered threads were very worn (too small of a male cone) you could screw and tighten the valve, but it would bottom out without properly engaging and loading the threads. In a theoretical extreme case only the tips of the threads would be loaded.

I totally agree about calling Mark Gresham at PSI. He could direct you to the appropriate codes.

 

[duckbill]

Yea, the valve in question isn't bottomed out. It still has several more uses left, for sure.

Thanks for the number. I'll give Mark a call come Monday.

I just want to know what's what, and if this is something I might run into somewhere else. It would bite to be on a trip and have the LDS there refuse to fill my tank just because they counted the threads

 

[james croft]

I am a PSI and a TDI inspector and have not heard of this. FWIW I have had trouble in the past with hydro facilities over-torqueing my valves making me having to ruin a valve or two to remove them from the cylinder. As a result none of my cylinders have valves installed when they go for hydro. I think somethings fishy here. I believe this guy is confused with the number of threads needed inside the neck. Under the theory this guy uses he would not be able to hydro my cylinders without a valve as he could not check my threads...

 

[owlbill]

Many of our cascade cylinders have barely a single thread showing, and we've been told that the valve is no good only when it does not seal (as far as the threads are concerned). FWIW

 

[oxyhacker]

I've never heard of such a thing. Taper thread valves tend to seat lower each time, as the neck stretches and the threads wear, so if you remove the valve enough times it will eventually be unable to seat correctly and not seal, but that's why they are made with extra threads - so that they will have reasonable service life. There would be no logical reason to discard a tank just because there are only three "extra" threads left - its not as if they wear in service, and you got to provide a reserve for wear the way you do with tire tread or brake lining thickness.

CGA C-6, the last word on steel tank inspection, says this:

"Cylinder neck threads shall be examined whenever the valve is removed from the cylinder. At manufacture, cylinders have a specified number of threads of proper form as required in applicable thread standards. Cylinders shall be rejected if the required number of effective threads is materially reduced so a gas-tight seal cannot be obtained by reasonable valving methods. More information on threads can be found in CGA V-1."

Later on it adds:

"The acceptance criteria for the continued use of cylinder threads shall require:
- at least seven continuous full threads for tapered high pressure cylinders, and at least 6 full threads for all cylinders with straight threads."

So as long as the tank has 7 good threads, and the valve seals, the tank is OK according to C-6. I don't have CGA V-1 handy, but it isn't one of the publications hydro shops are required to have, so it is unlikely to add anything that would contradict C-6.

BTW one especially irritating thing about this is that, even if you accept the three-exposed-thread theory, it would be, without further investigation, impossible for an inspector to know whether the problem was with the tank or the valve, So to condemn the tank on the basis of how one random valve fits would be foolish.

 

[redacted]

I've got to wonder how many new tanks the shop has sold with that story.

 

[Bob3]

The shop owner *might* be confused with the FAA requirement that specifies a minimum number of threads exposed on a bolt after the nut is run down. (2 or 3, I forget which)
If the valve were run into the neck & had neck threads exposed, THEN I'd sure worry.
Nothing I've ever heard specified requirements for tank valve threads to be showing; time to go hunting for a new shop methinks.