Old 72 question

[Bob DBF]

I’ll have one tested, the others are not worth it to me. I’ll do something with them, eventually

You might find someone in your area that wants older/odder vintage tanks and swap for 72's with 3/4 threads, just keep the word out.


Bob

 

[2airishuman]

The other looks to have 1/2 threads, can these valves can be found ? Can I get one with DIN?

Hi MaxE

I believe the valve in photos you shared is of a valve with M18 threads. I had one once.

M18 threads are still in use internationally and DIN valves are available from Chinese sellers on ebay (though they are not "provalves" and will not accept a yoke regulator even with an insert). You may also be able to clean up the valves you have. I would highly recommend replacing the PRD (burst disc) assembly, see my post in A&I for reasons.

As for the 1/2" tapered threads, well, I've had those too, still have one on a pony cylinder that I like. They are a nuisance in the era of VIPs as the threads wear every time the valve is removed and reinstalled, so you have to replace the valve every 5-10 years. Most dive shops cannot torque them properly and use the wrong thread sealant, so they leak. As noted upthread, valves are available but are expensive, making these cylinders uneconomical to keep. That said, the packaged gas industry still uses tapered threads, so they can work out OK.

 

[Rick trettin]

I have a question that I can’t find answer for on the internet. I have a healthways tank with a 1/2 npt valve. Some time ago a took the tank in for a VIP and the tech, said the valve was no longer good because three treads would not show when valve was reinstalled. I can’t find anywhere that this is a requirement. Does anyone know where he got this information? The first valve was the original that come from the manufacture. I bought a different valve online and he was happy with and it was installed. Different brand. I see photos of other tanks online that are tapered valves that only have a one or two threads showing.

 

[tr3a]

Never had anyone complain about my pipe thread 72’s.
That said, McMaster has a mil-spec teflon tape that is slightly thicker (very slight difference) but using it makes a world of difference. Remember it needs to be tight but you do not need to bury the valve in the tank. Some of my valves are from the 50’s and they are still fine

 

[2airishuman]

I'm not sure what the exact requirement is but technically for CGA comliance the valve is supposed to be torqued a specific amount and still have some number of threads showing. I thought it was just one full thread but I could be mistaken. With tapered threads the threads on the valve do wear with each reinstallation which limits lifespan especially if removed annually for VIP. The cylinder threads wear also but at a much lower rate. The packaged gas industry has oversize valves available with either one or two threads of extra diameter that can be used as cylinders wear but I've never seen an oversize scuba valve.

 

[Rick trettin]

Thanks you both for the info. It just seamed odd to me this was never brought up before. There were some threads showing, but it wasn’t three. This was a new guy the dive shop hired. I did a thread repair on a twin manifold burst disk thread also. The first guy didn’t have a problem with it but the new guy did. Some one tried to removed the burst disk with a hammer and screwdriver. This was for an old set of 40’s. I machined the threads out and installed a stainless steel threaded insert. I’m not sure many people know this but due to the size of hole In a burst plug, there is only about 80 psi against the disk at 3000 psi tank pressure. That’s why disks are so thin. Of course anything on your body couldn’t stand 80 psi on that same area. He doesn’t work there any more so who knows.

 

[Rick trettin]

Rick, here. I meant to say there is only 80 pounds of force on a burst disk not 80 psi.