Strange Valve on Steel 72

[kramynot2000]

So I decided to pick up some steel 72's for a little pair of doubles and got a couple of PST's from the 70's. Unfortunately I've got LP72-itis and have found myself looking for more. I found an old US Divers tank from the 60's with a 3/4" valve which I decided to pick up because it was only $10. The valve is one of those post valves that look like the old 1/2" valves. I figured I'd just replace it with a newer valve when I got home. Unfortunately, I found that the newer 3/4" valves that I have don't screw all the way in to this old tank. When I compared the original valve with a newer valve it is clear that the threads on the old valve are shorter.

I thought the only valves on these LP72's were the 1/2" NPT and the newer 3/4" thread valves but I guess I'm wrong. I'd really like to replace the old post type valve with a newer one but have no clue where or how to look. Is there a source for short 3/4" thread valves? If not, I guess I'll just rebuild this.

thanks,

 

[lowviz]

So I decided to pick up some steel 72's for a little pair of doubles and got a couple of PST's from the 70's. Unfortunately I've got LP72-itis and have found myself looking for more. .......

I have a bad case of that myself.

Your post gave me a moment of concern, just bought a 1972 cylinder to complete a twinset, have to make my own 'Highland style' bands as I couldn't find anything commercial. The 72's give a wide tank-to-tank gap on my 8.5" Dive Rite manifold so I had to use a 1/4" 304SS plate on each band to get the required stiffness. Nearly done, just have to fit and TIG-weld the second band.

-Getting back on topic, I'm at a loss as to what threading you have. Just checked, mine works perfectly with the new DR manifold. Maybe re-post in the antique gear forum?

 

[rjack321]

Apparently the tap wasn't run all the way through the neck on this tank when it was made?? Can you take a pic of the valve that came on it and the hole?

 

[sea_ledford]

It might be a tapered valve too. I think most of those old I-valves were... hey someone should reintroduce them and call 'em iValves. They'd have to come in white, or black for little more $

Chris

 

[captain]

As someone said the problem is the thread on the tank wasn't cut deep enough for the new valve. From your description it sounds like the first 3/4" K valve USD made which was like the prior 1/2" valve with the wing nut on top. Unless you want to use a DIN valve just use what you have or a later side knob K valve. About the only failure a valve is subject to is the diver not opening it before jumping in.
Or you can machine off enough of the threads on the new valve to allow it to seat.

 

[Luis H]

Look inside and inspect the threads. I am willing to bet the threads are there… they are just dirty and with some corrosion. You may need to run a tap just to chase and clean the threads.

I have seen this happen several times. With the short valve, the unused threads get some dirt and when you try to screw a deeper valve it doesn’t let the valve screw in any further than the old valve.

The dirt can be just tiny specs of rust that get trapped in the threads due to the silicone grease that was used to lubricate the threads.

If you don’t have a tap to clean the threads you can just try a wire brush.


Good luck

 

[kramynot2000]

Out of town right now but I'll take a look inside to see if the threads are there, which hopefully they are, and take a pic of the valve.

 

[lowviz]

Can't find any mention of tapered 3/4" threads ever being used on 72's. So I'm guessing it would be easiest to chase the tank threads with a (3/4"-14 NPSM) tap as previously suggested.

Throwing in this link just for fun:

Vintage Scuba Diving Community Forum - Where Did Steel 72 Originate

 

[kramynot2000]

Well, turns out the threads were there, there was just a little corrosion etc. I used a wire brush and now can get a newer valve screwed in.

Thanks,