Can anyone identify this valve?
- Thread starter Shaun_Mc
- Start date
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From all I have ever seen and heard of that valve will not be as supplied from the factory.
While I have never seen or heard of an actual requirement (CGA, DOT etc.) cylinders with pressures of 3500 PSI and above are always DIN. The best I can call it is an unwritten law. Note that HP cylinders sold with convertible valves have had the service pressures trimmed, usually to 3442 PSI.
I have however heard of divers having machine shops modify the larger 3/4 NPS valves to the smaller 7/8 fine thread used on those Genesis (PST) cylinders. Have you seen the valves out of the cylinder to verify that the threads are still chrome plated? Alternatively is there any chance this came from overseas?
I'd be very interested in common "K style convertible valves for some of my similar cylinders.
Pete
While I have never seen or heard of an actual requirement (CGA, DOT etc.) cylinders with pressures of 3500 PSI and above are always DIN. The best I can call it is an unwritten law. Note that HP cylinders sold with convertible valves have had the service pressures trimmed, usually to 3442 PSI.
I have however heard of divers having machine shops modify the larger 3/4 NPS valves to the smaller 7/8 fine thread used on those Genesis (PST) cylinders. Have you seen the valves out of the cylinder to verify that the threads are still chrome plated? Alternatively is there any chance this came from overseas?
I'd be very interested in common "K style convertible valves for some of my similar cylinders.
Pete
Scared Silly
Contributor
What is interesting is that the cylinder is an exempt hp cylinder HP3500 psi. Which means that the valve should be a 7/8" - 14 UNF neck and 7 thread DIN valve (aka 300 bar). However, the valve is convertible valve (5 thread - 200 bar). As such, if the valve is removed I bet that you will find the valve has been re-cut to 7/8" - 14 UNF from 3/4" NPS.
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That tank had a 0.875-14 UNF neck thread, usually called a 7/8.
The square back of the valve looks like an early DiveRite, but it may have been made by someone else, or maybe SeaElite?
The square back of the valve looks like an early DiveRite, but it may have been made by someone else, or maybe SeaElite?
cool_hardware52
Contributor
That would be a pretty good trick, given that 7/8" x 14 is smaller than 3/4" straight.
Tobin
kwinter
Contributor
Tobin beat me to it. It is a common mistake to think of the 7/8 neck being bigger than an standard 3/4, but it is actually smaller. UNF is measured differently. You can recut a 3/4 valve to fit in a 7/8 neck, but not the other way around.
BTW, it's hard to tell from the photo, but I couldn't swear that is a 7/8 neck tank. If you can remove the valve, see if a quarter will fit through the neck. If it does, that's a 3/4 neck and a standard valve.
BTW, it's hard to tell from the photo, but I couldn't swear that is a 7/8 neck tank. If you can remove the valve, see if a quarter will fit through the neck. If it does, that's a 3/4 neck and a standard valve.
R
redacted
Guest
That would be a pretty good trick, given that 7/8" x 14 is smaller than 3/4" straight.
Tobin
I think the idea is the valve threads were re-cut, not the tank threads.
OP
Shaun_Mc
Registered
The tank is a Genesis 120 7/8" neck
More specifically it is almost certainly a PST cylinder re branded for Genesis. First of all this is very common, secondly while I didn't spot PST on any photos I do see the stylized CL hydro symbol from Cochran (SP?) Labs, they did a lot of the testing for PST. PST also branded them for USD and others.
To be more explicit on explaining the thread relationship....
These cylinders have a 7/8" UNF (fine) thread. This is a bolt thread and the OD of the bolt is essentially 7/8". The female thread is sized accordingly.
The 3/4 NPS (National Pipe Straight) is the non tapered cousin of NPT that you see on common plumbing pipe. Pipe sizes are based on the INSIDE diameter of the pipe. Since the wall of pipe is substantial the male thread on the end of a pipe is much larger than the trade size. Hence a 3/4 NPS thread is much larger than a 7/8 UNF This means that there is adequate material on a common 3/4 NPS valve to cut a 7/8 UNF thread.
For a spell they cranked out a slew of these babies in various capacities. I have 4 of the 100 CF capacity and would love to have yoke valves so I could mount my double hose regulator on them. They can often be found out of hydro for small money and if you can live with (or prefer) DIN they are a bargain compared to a new 3442 100 CF cylinder. I essentialy had the 4 of mine in service with fresh hydros for the cost of 1 new 3442/100 PST or Worthington cylinder.
Given today's cylinder marketplace they may be even more desirable.
So the question remains, are your valve threads plated or raw machined brass?
Pete
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