Force vs Pressure vs Surface Area and Tank Valves

[2airishuman]

There are some early LP72s that had M18x1.5 metric threads (with an o-ring) that are very close to 1/2" npsm. Perhaps that is what you have.

M18 valves with scuba regulator connections are available on ebay etc. These threads have been used for SCBA tanks and various other applications for many years.

 

[2airishuman]

3/4" valves don't break even when hydro pressures are applied (5000-5250psi+ that's how burst disks burst) so whether 1/2" is stronger or not is not really relevant.

I always thought hydro tests were performed without the valve. Perhaps I was mistaken.

 

[Bob DBF]

I always thought hydro tests were performed without the valve. Perhaps I was mistaken.

I think it is more of a reference number divers can relate to than anything else. The burst disc would prevent a proper hydro, and probably give the operator ptsd over time. Hydros are done without a valve.

 

[Ghost95]

I have 3 tanks with 1/2" valves. Two of those are doubled 50's on a White Stag manifold and the other is a Sportsways valve on a steel 72. The old Sportsways catalog list their valve as a 1/2" straight pipe thread so that is what i'm going by and I haven't seen a White Stag catalog with my particular set listed. Well, that and what other vintage guys have posted though I have not measured the valves my self. The valves work in the tanks they are in and if I decide to have valves turned down to fit I'll include these valves as a reference.

The valves are in great shape. The "J" valve even works. The reasons I'm looking to swap them out are minor, ergonomics when carrying, ability to use a DIN without an adapter, and separating the doubles. The valves work fine now though and I dive them as is without a problem.

 

[Ghost95]

I missed the "S" in the original post but 1/2" NPS? I don't think those were (ever?) made. Lp72 tanks of the vintage had 1/2" NPT threads so they take Teflon tape not straight thread Oring seals. Do you have the tank and what valve is in it now? Any pictures of the tank and valve?

You definitely cannot have a NPT tank tapped and rethreaded to anything.

I may be able to find a couple better pictures of the tanks later but you can see the setup in this thread.

My descent into Vintage!!!!

I have since finished the rebuild and am now just waiting to get home and dive the set. The machining of new valves is just an idea I'm toying around with.

 

[captain]

I missed the "S" in the original post but 1/2" NPS? I don't think those were (ever?) made. Lp72 tanks of the vintage had 1/2" NPT threads so they take Teflon tape not straight thread Oring seals. Do you have the tank and what valve is in it now? Any pictures of the tank and valve?

You definitely cannot have a NPT tank tapped and rethreaded to anything.

Sportways had 1/2" NPS tanks and valves for a short while before 3/4 NPS became the standard

 

[Alekseolsen]

Slightly off topic, but this (old) thread was quite close to what I wonder.

I've found an old Scubapro double-4 liter set. I'm considering purchasing and splitting them up for some "expedition sidemount dives". The thing is they have M18 neck. Is that appropriate to breathe from? I've found valves, that will gir a first stage, but unsure about capacity etc. Deepest dives in the cave-system we had in a week was 6,1 meters, thus 4-liters should be OK.