Tank Valve thread opening?

[Pappy5]

Good Morning,
New open water diver here.
I was given a set of double Norris Steel 2250 tanks by a friend that can no longer dive. They were setup with a double manifold .
They were 1973's with the last Hydro/Inspection 1977. I had them Hydroed and tumbled. The facility that did the test said they were in great condition. I want to use them as single tanks to mess around in my pool and was needing to buy new valves.
I bought a Thermos 3/4 valve thinking it was the standard but it's to small, does this mean it's a 7/8 opening on the tanks?
I have included pictures measuring the threads on the valves with my calibers. The 1.025 came off the old tank and the the 0.872 is the new valve thats too small. What size valve do I need?
Thanks for any help.

 

[Diver0001]

Is it possible that one reading was on the threads and the other was between the threads?

R..

 

[Pappy5]

Diver0001,
These are two different valves. The bigger one 1.025 came off the old tank and the smaller one 0.872 is the new valve I bought that is too small for the tank opening.

 

[JamesBon92007]

That's odd. I only know of two main sizes for that era: 3/4" and 1/2" with straight threads. Before that there was 1/2" tapered threads. I don't have any calipers but my 3/4" valves measure roughly 1" with a tape measure. Are you saying that the two valves are different sizes? That seems terribly unlikely. I never did understand plumbing sizes so I can't tell you why a 3/4" valve measures 1" but that seems to be how it is. My 1/2" valve measures just under 3/4". Do you happen to know the capacity of the tanks? Are they 72s? Do they say ICC-3AA 2250 on them? I also am not familiar with a "Thermos" valve. Where did you get it and when was it made?

If the tanks are what I think they are then just about any 3/4" Sherwood , US Divers, or Sportsways valve (plus others) from that era (or later) ought to fit. The only thing I can think of is that your Thermos valve must be 1/2" and whoever you bought it from didn't know what to call it. It is WAY too small?

Aside from all that, very cool acquisition! I'm sure you will enjoy them once you get the valve thing figured out.

 

[guruboy]

I think you bought the wrong new valve. A 1/2" valve is around 0.850

 

[grf88]

Just measured a 3/4 in valve and got 1.027. I think guroboy is correct in thinking you have the wrong valve. It looks like you ordered the correct one if you ordered a 3/4" Thermo but it appears they sent you a 7/8 UNF valve.

 

[DogDiver]

Have the original valves rebuilt and have the openings for the crossover manifold plugged.

 

[Jack Hammer]

So it gets confusing. A 3/4 or 7/8 valve size isn't the actual physical size of the opening, it's a designation. Most US steel 72s from the 70s use a 3/4 valve. To make it more confusing, a 7/8 valve is actually smaller than a 3/4. I suspect you have a new 7/8 valve and just need to get a standard 3/4 valve instead.

 

[grf88]

Good information on valve types and thread sizes can be found here
Valves & Neck Threads | Dive Gear Express®

 

[Pappy5]

Great information and exactly what I was looking for!

I think you bought the wrong new valve. A 1/2" valve is around 0.850

Just measured a 3/4 in valve and got 1.027. I think guroboy is correct in thinking you have the wrong valve. It looks like you ordered the correct one if you ordered a 3/4" Thermo but it appears they sent you a 7/8 UNF valve.

So it gets confusing. A 3/4 or 7/8 valve size isn't the actual physical size of the opening, it's a designation. Most US steel 72s from the 70s use a 3/4 valve. To make it more confusing, a 7/8 valve is actually smaller than a 3/4. I suspect you have a new 7/8 valve and just need to get a standard 3/4 valve instead.

Thanks to All
Pappy