Steel Tank Threads - what happened to the 7/8-14 2A UNF?

[Jimmer]

I'd take those tanks and a manifold for $300. My instructor has been diving the same 4 Genesis Hp100's with the 7/8" valve for over 10 years and they are still his primary tanks today. He's never had a reason to switch to new Hp 100's.

 

[rjack321]

Yeah $300 is a deal. Those should be last for decades. Just be really careful with your 7/8" mainfold. Its hard to replace those nowadays. Otherwise, I have no love lost on 7/8" valves, what a pain to service and inspect. And the funky angles are unnecessary and silly.

I just wish there was some way to ensure that M25 valves don't get mixed in with 3/4". Not that they would in my small garage fill station universe, its just dumb to have 2 seemingly compatible threads floating around.

 

[Jimmer]

It might not be that hard to replace that manifold, Thermo still makes one, as does Genesis. My instructor scored a really nice Dive Rite last year for his.

 

[VintageSCUBA]

Lesiure Pro sells the Genesis dual outlet manifold for the HP tanks (7/8-14 threads) for just a tad over $200.00

 

[rjack321]

Lesiure Pro sells the Genesis dual outlet manifold for the HP tanks (7/8-14 threads) for just a tad over $200.00

Really?? Learn somethin' new here I thought the 7/8" manifolds were in limited/sporadic production since those tanks aren't made anymore.

 

[The Chairman]

You will never have a non-HP tank with a 7/8" thread per the DOT.

You will never have an HP tank with a 3/4 thread per the DOT.

Reducing the pressure by just a few PSI was a tremendous idea by the tank manufacturers and I think PST gets the credit for first figuring that out. Having non-HP valves on a tank gives us options for using a yoke regulator that we can't have on an HP tank. This all goes back to the development of the "Sport Din" by Scuba Pro.

As for the disparity of the size of the opening to it's sizing, it's because its a pipe thread. When pipes were first designed, the OD meant nothing. However, the ID of the pipe determined how much water could pass. Consequently, pipe fittings are sized by the mean ID of the pipe and not by the OD of the pipe, which is how bolts are sized.

The first tanks used tapered threads which were sealed with the use of a little "pipe dope". The current batch of tanks use a straight pipe thread and seal with an O-Ring. This resolved a TON of issues as the tapered threads were slightly enlarged every time the valve was installed.

 

[Leadking]

I would think that most divers would appreciate the use fo 3/4x14 thread. The standarization of valve threads simplifies most everything. If you want a DIN connection, the 200 bar DIN is readily available.

By the way if you think the European connections are better, wait "til you see the mandated nitrox connection comming down the pipe!

 

[The Chairman]

BTW, if you ever tumble tanks, you will appreciate the BIGGER diameter of the 3/4" straight pipe thread. The media doesn't get lodged in there at all.

 

[DA Aquamaster]

By the way if you think the European connections are better, wait "til you see the mandated nitrox connection comming down the pipe!

This is going to sound a bit euro-phobic, but I am getting SOOOOO sick of European standards being adopted in the US just for the sake of commonality between products sold in the EU and in the US due to EU requirements that are often stupid, meaningless or designed to give European products a marketing advantage.

A decade ago the EU threatend mandate was left handed threaded DIN valves for nitrox use. At the time it made a limited degree of sense, but now that 1. most "air" is now filtered well enough to meet O2 compatible standards, and 2. the need for dedicated tanks and valves is largely irrellevant given the move away from partial pressure blending to stick and membrane systems that make the need for 02 clean tanks much less common. And 3. for O2 service, what really counts is better vlave design with slower rises in pressure (slower opening) and smoother porting and flow paths and that will be a function of the valve design itself regardless of the valve connection used.

 

[Luis H]

You will never have a non-HP tank with a 7/8" thread per the DOT.

You will never have an HP tank with a 3/4 thread per the DOT.

Could you refer me to the document (Code of Federal Regulation) number that regulates pressure vessel thread sizes?