pony bottle / welding bottle?

[hbhobby]

I am new to the board but not diving. I have a question about tank threads. I have 20.5 CF tank that was used for Oxygen for a welding unit, I want to use it as a pony bottle. The threads are very simular and a tank valve wil screw in mostly (threads need to be cleaned up) is there a problem with using this takn as a pony bottle?

 

[dannobee]

Welding tanks have tapered pipe threads, scuba tanks have straight threads and an o-ring. I suppose you could get one of the old, old steel tank valves with tapered pipe threads.

Do you know the buoyancy characteristics of the tank, and how are you going to mount/sling it?

 

[Graeme Tolton]

I would be willing to bet that the welding o2 bottle has 3/4NPT (.75" National Pipe Taper) Threads. I would also be willing to bet that your scuba valve is 3/4NPS (.75" National Pipe Straight) threads. So, unless you are able to find a 3/4NPT scuba valve, you are SOL. The valve will screw in (most of the way as you describe), but will not be a proper fit. The other problem is that NPT threads are sealed by the taper of the threads, while NPS valves are sealed by an o-ring on the valve that fits into an o-ring groove at the top of the neck of the cylinder.

The only viable option that i can see in this case would be to find a 1/2"NPT scuba valve (these are becoming rare) and use a 3/4" - 1/2" NPT bushing. However, getting this filled may pose to be a problem.

Other than that.... even welding o2 cylinders have to be o2 clean to prevent fires....

 

[Gen San Chris]

O2 cylinders are usually rated at a lower fill pressure so you would not get the same fill as a custom made HP pony bottle!
If you have to get bushings etc made up you will probably save money by getting a new one!

 

[Stu S.]

Here is a dive store that has a lot of old parts and pieces. The place looks like it hasn't changed in 35 years. If you can't find something that fits, Keith may have it.

Scuba Lessons Orlando Florida

 

[hbhobby]

thanks for the information. now that I have checked it with the micrometer the tank is taper thread and will not work (probably should have checked that first) but thank you for the information