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

[veriqster]

Just so you don't feel like you wasted you money I'll take them off your hands and even pay for shipping, ...

You guys are making me feel really bad I just picked up a set of double HP100's (PST),a Dive-Rite Manifold and bands as a set but they have the 7/8-UNF thread. Now I feel like I wasted $300......

 

[vshearer]

Just so you don't feel like you wasted you money I'll take them off your hands and even pay for shipping, ...

Thanks but... Y'all just keep on bashing 'em. Drives down the price for the ones out there, and I don't have to worry as much about someone walking off with mine

(Tumbling is a bieotch though)

 

[VintageSCUBA]

You guys are making me feel really bad I just picked up a set of double HP100's (PST),a Dive-Rite Manifold and bands as a set but they have the 7/8-UNF thread. Now I feel like I wasted $300......

Hello vshearer,

Don't worry or feel bad. You made a very good buy. I have and use three set of doubles. (2) are HP steel Genesis tanks with Genesis iso manifolds, with the 7/8-14 threads. They are a set of 80's and a set of 100's. The third is a set of LP steel 60's with 3/4-14 NSPM, also with a Genesis iso manifold.

 

[pescador775]

WRT DOT mandates, it is doubtful if they exist. I presume that the 7/8-14 threaded neck was to protect PST from liability. The specific thread is actually not important, it just had to be different. PST, following some CGA or DOT guidelines concerning yoke clamps, and wanting to imitate European practice, specified a new, exclusive, tank neck size for an American style HP DIN valve; thus, to prevent yoke screw valves from being fitted to their 3500 psi tanks. Later, coincidentally following my rants on the subject, they acquiesed to making HP tanks with 3/4 necks using a minor subterfuge of reclassifying the tanks as MP (medium pressure). This was cleverly done by exploiting the differences which exist between Europe and the USA with respect to engineering definitions of STP (standard temperature-pressure). The 3442 psi tanks are the result.

 

[WD8CDH]

The 7/8-14 thread was and still is a common thread for 4500 SCBA tanks. It was as simple a choice as any if the manufacturer wanted something different for 3500psi since hydro centers had the fittings.

But 3/4 NPS will handle 3500psi or even 4500psi following DOT specs.

 

[pescador775]

WD, right on. Following the checkered history of such practice, the dive industry abandoned the 7/8 UNF neck thread, just as they did the 1/2 NPS thread also used for SCBA tanks of the time.

 

[Codyjp]

I just bought a double set of these 'genesis' HP100's. bands, manifolds for $250+ a fresh hydro. I am happy! I also just bought a set of regular valves in case I decide to break them up. for $20/each I though it was worth it!

as a side note, they were original manufacture date of 1992 and they passed hydro no problem.

 

[VintageSCUBA]

Codyip,

I think you got yourself a good deal there.

 

[Codyjp]

yup. I did my first dive with them and I loved it. they are great. I am going to keep my eye out for more of them!


all said and done they cost me $330 with a fill included. Can't beat it. The shop also said they looked great inside. Just like new!

 

[mheaster]

I totally agree with DA Aqua Master (this is not uncommon).

Since the area of the opening is a square function of the diameter, the small inside diameter difference can make a big difference in servicing and inspecting the tank.

IMHO going to any thread size smaller than the present standard of ¾”-14 NPSM is a bad…bad idea. As a kid working on a dive shop (back in the early 70’s) guess who gets to do the old dirty job of tumbling tanks.

I am down to only a few vintage tanks with a narrow neck and will not touch any ½” npt tanks unless it was given to me…and then only to be polite.

I was given recently an old Sportways with the old straight ½” straight pipe thread, and I kept it because it is cool. I was lucky that I was able to service the valve and it is OK because that is probably one of the hardest valves to find.

I know this is an older post but can you (or anyone else) provide me with any fiuther info about Sportsways Straight 1/2" valves? I recently purchased two vintage steel 72's with a Sportsways manifold and bands. I found a 1971 Sportsways Partslist and repair manual with a parts drawing but it describes a "3/4-14 NPSM Straight Pipe Thread SJ2 Valve Manifold" in it that looks for all the world like mine but mine is a 1/2" version so I assume it is earlier than 1971? Anyone know anything more about timeframe of 1/2" use?

I have just sent them in for Hydro and don't have them in front of me.

ANY discussion and opinionsa re welcome other than "You are an IDIOT and wasted your money!" lol

I would like to use them as a "break into doubles set " at local quarry (if nothing else) and for the price, have no problem doing that!

In a perfect world IF at all possible, would like to get them cleaned, valve serviced and set up for Nitrox. (I may have to do that work myself)