Older DIN valve with odd bottom diameter.

[Luis H]

Here are some links to tapered pipe threads dimensions:

Dimensions - Pipe Threads

Basic Dimensions for NPT American National Taper Pipe Threads

From your description it does sound like you do have tapered 1/2 inch pipe thread.

If it is a tapered thread, the valve will get progressively tighter as you thread it into the tank and even after you tighten it all the way, you should always see some threads.

With a straight pipe threads there should be provision (a small recess) on the tank neck for an O-ring. And the valve should thread easily in all the way and would only stop when the valve shoulder (ring just above the threads) comes in contact with the top edge of the tank neck.

Was there no O-ring on the neck?

Can you post a closer picture of the valve threads and tank neck? If you can provide some closer pictures it should be fairly easy to tell them apart.

 

[Leadking]

It would be almost impossible, and I don't know if someone did it as a joke, but here is the bio of P Talliez

Philippe Tailliez - Wikipedia, the free encyclopedia

I met him years ago in New Orleans-he taught Jacques Cousteau to dive.

 

[minimalistdiver]

I think what I am going to do if this tank passes hydro is try to get the cheepest deal on a DIN valve that I can. It is a half inch taper. So I will either try to find a DIN valve already configured at half inch taper, or get an inexpensive .75 DIN valve and get it machined to half inch taper. I know a machinist that might do it for cheep or maybe trade me for this service. I know XS Scuba makes one that will fit for $100. But that will make this project cost prohibitive, because for $180 I can get a nice used aluminum tank from my LDS.

$5 for the tank
$50 for visual and hydro from LDS
$20 to $30 for tumble
$30 to $40 for a used DIN Valve

 

[scotthowes]

Check EBAY I found a uaed 1/2'' valve with shiping $14

 

[captain]

It would be almost impossible, and I don't know if someone did it as a joke, but here is the bio of P Talliez

Philippe Tailliez - Wikipedia, the free encyclopedia

I met him years ago in New Orleans-he taught Jacques Cousteau to dive.

Could it really be a tank once owned by Philippe Tailliez, intriguing.

 

[Gilldiver]

Question: Why do you think it has to be tumbled?

A little spot rusting is very common with steel tanks and can be removed quickly with a whip. In 33 years of diving I have never tumbled a tank and have only bought 3 tanks new, the rest have been "used" dating from 1960 up to the new tanks which were made in 2003.

 

[minimalistdiver]

Gilldiver,
It is just a few patches of rust. kind of looked like scabs What is a whip? Perhaps if I get a "whip" I can touch it up myself.