Tank threads

[Ron Hearn]

Hi

I have a question concerning older scuba tanks, I've seen in a few photographs pictures of tripple tank set up and noticed the the valves are mainly 1/2 inch thread that look like they are inserted into what looks like a coupling inserted into a 3/4 in threaded tank, am I seeing this correctly or is it just a rim thread design, are there any differences in 1/2 thread sizes over the years.

Thanks

Ron

[SeaRat]

Ron,

At the time, the standard for scuba cylinders were 1/2 inch tapered threads, and the cylinders matched if they were scuba cylinders.

Many divers converted fire extinguisher bottles into scuba bottles, and needed to use a converter plug to do so and match the scuba manifold's 1/2 inch tapered threads.

SeaRat

[on Hearn]

Thanks SeaRat, this now explains what I have be seeing.

Ron

[VintageDiverMN]

If you buy one of those fire extinguisher bottles with reducers, you will have trouble getting them filled. Dive shops won't fill them, you would need to have your own compressor

[John C Ratliff]

Ron,

I did not see the part about your seeing this on triple tank systems. You would have to inquire of the owner, but there is another reason for using an adapter for triples. They could be either converting UDS-1 system tanks (which are 1" threads) to an older triple valve by, say Nemrod, which were 1/2 inch threads, or they could be regular 3/4 inch scuba tanks trying to mate to the older 1/2 inch manifolds. There were not too many triple manifolds, and the newer 3/4 inch ones are in very short supply.

SeaRat