PST 3500psi tank help

[Jaxman78]

Let me first say I am new to diving so be easy on me…lol. Anyways, I just acquired two PST 3500psi steel tanks for free. The guy was moving and left them on the curb for me. They are in great shape and are currently being hydro/VIP. They have Thermo 3500 DIN valves on them with ½ inch inlet. I asked my LDS if it was possible to put yoke style valves on the tanks and they said it was, but the valves are hard to find. Either he was right about being hard to find or wrong cause they don’t make them because I cant find them anywhere on the web.

I have just decided to convert my regulator to DIN and buy a yoke adapter when I use tanks with yoke valves.

Anyways, my question is…was the LDS staff right about the valves and where can they be found? From what i have read i dont think they make a yoke valve thats rated for 3500psi...

Thanks for any help..

 

[Bubbletrubble]

I bet you're talking about the 7/8" UNF DIN tank valve. I own several older PST HP steel tanks.
AFAIK, you can't install a yoke tank valve on those tanks. They are great tanks, though.

I'd recommend converting your reg from yoke to DIN. It will cost you $40-$70. While you're at it, purchase a spin-on DIN-to-yoke adapter and carry it in your save-a-dive kit. You never know when you'll need to use a yoke tank valve.

Considering what you paid for the tanks and assuming that both tanks pass hydro and VIP, I'd say you made out like a bandit.

 

[Troutmaster]

Those tanks are worthless, just let me know where to pick them up

Bubbletrouble is exactly right, switch your first stage to DIN and carry a yoke converter just in case, well worth the expense given the fact you got two free tanks out of the deal.

 

[Scared Silly]

Anyways, my question is…was the LDS staff right about the valves and where can they be found? From what i have read i dont think they make a yoke valve thats rated for 3500psi...

Yes and no, some where made but IIRC they were bootlegged 3/4" valves that were turned down to 7/8" UNF. Converting to DIN was the right move consider it the cost of free cylinders.

BTW IF you get them hydro'd get the PST guidelines on round out the cylinder before doing the actual hydro measurement. Some shops do not do this step and in return the cylinder fails the test.

 

[spectrum]

I have some of those and they are nice cylinders. They are the predecessors to the PST E7 series and the Worthington X. In the latter incarnations they shaved the capacity to 3442, getting them under the 3500 yoke limit. The source of the limits seems to be an enigma but it is the industry standard. Given some yoke O-ring failures it seem prudent enough. but I digress.

Using these cylinders means regulators that are in the DIN configuration. you yoke outings you can convert back or use the inline adapter.

The bootleg valves are rare and an on the ball by the book shop would decline to fill for obvious reasons.

If you are scratching your head about the contradictory valve sizes it is the thread systems. Your 3500 cylinders have 7/8 fine threads, like a bolt and are nominally measured across the outside of the male (valve) thread. The more common 3/4 NPS thread is a pipe thread (straight, not tapered) where 3/4 is the ID of a pipe to which the walls of the pipe are added making the actual valve larger than the 7/8 NF counterpart.

Good luck with the recommissioning!

Pete

 

[Jaxman78]

Thanks for all the advice. I assumed the threads were ½ inch because that’s what the LDS said they were. The 7/8” make more sense and is easily found on the internet.

I asked this question on the Regulator thread but haven’t received any insight…..The conversion DIN piece for my Atomic Z2x is $90. I have a Scubapro regulator with DIN. Will the scubapro DIN fit on the Atomic? I was told it would not.

 

[Bubbletrubble]

@Jaxman78: In general, it's good practice to assume parts like that (DIN connector, handwheel, etc.) aren't interchangeable between two different brands. If they are, it's a happy coincidence.

If you have an Atomic reg, be sure to purchase the official Atomic part.

 

[2TH DIVR]

I have one of the first Dive Rite 7/8 manifolds and it's 200 bar.
Never had a problem getting a 3500 fill.
Use din on all my regs except the Pheonix double hose and never lost an O-ring using the insert.
Love my HP 100's

 

[MajorJohnson]

I went through all this research to try to convert my beloved blue Sherwood to yoke and there is just no simple way.

1. Nobody makes a yoke valve that will fit the threads on your tank.
2. The spin in adapters won't work because the threads on the DIN portion are too deep for the regulator to seat on the spin-in insert and the front-to-back distance of the valve is too large to fit through any yoke I've seen.

The only way I can find to use a yoke on these tanks is to machine the DIN thread on the valve from the DIN 300 length to the DIN 200 length used on the current crop of convertible valves, allowing it to fit inside the yoke and allowing the use of the spin-in inserts. You may also need to drill a tiny dimple on the back side of the valve to keep the yoke screw centered. I believe these valves are chrome plated brass, so the cosmetics will not be perfect.

I could not find anybody to tried this method, but I'd love to know if you give it a try.

 

[rjack321]

Thanks for all the advice. I assumed the threads were ½ inch because that’s what the LDS said they were. The 7/8” make more sense and is easily found on the internet.

They are 7/8ths UNF.

1/2" threads do exist, just never on those tanks. They are a very very old thread type used on some 1950s-ish lp72s and such. They seal with teflon tape instead of an o-ring.