HP100 PST 3500 DIN/Yoke Issues

[runsongas]

Because the 7/8 unf fitting is physically smaller than the 3/4 nps, it is possible to rethread a 3/4 valve down to a 7/8. You just need the tooling.

 

[Scared Silly]

Because the 7/8 unf fitting is physically smaller than the 3/4 nps, it is possible to rethread a 3/4 valve down to a 7/8. You just need the tooling.

Exactly the valves shown in this thread and in the link advert were originally 3/4-14 NPS which have 5 threads and accept a plug for yoke valve. They have been rethreaded to be 7/8-14UNF.

That said XS Scuba is making a 7/8 valve but as is the standard are 7 thread DIN only.

 

[2airishuman]

That is obviously not the OEM valve that came with the tank. Valve shoulder should match up with the tank neck. Dimple on the back will not be there on the OEM 3500 psivalve.

I wouldn't be so sure. I have one pair of 7/8" neck cylinders, and the (300 bar) valve shoulders overlap the tank neck somewhat, similar to the photos upthread. I have several 300 bar valves, from various makers, that have the dimple.

Thats why I said you were not "exactly" right. We can talk about the factory all day long, but to say that a PST 3500 tank will NOT take a yoke or is ONLY 300bar DIN is not correct. My PSTs clearly have a 7/8" valve that is NOT 300bar DIN and a yoke reg DOES fit on there.

I suppose it's possible that some such valves have been made, by someone, over the years. I've never heard of one until now. It is also possible that the valve was modified by someone after it was made, either by cutting 7/8" threads on a 3/4" valve, or by machining off part of the DIN fitting.

 

[Doby45]

Well the "unicorn" has been found.. I think someone else ran into this "impossible" proposition before. Classic case of not speaking in absolutes when you make a statement..

 

[2TH DIVR]

The early Dive Rite manifolds for the PST 3500 tanks were 200BAR
I have 3 of these manifolds
they are now broken down to singles for the type diving I do today
Yes, there are some yokes that will not fit over the valve , like the Conshelfs with tapered yoke

 

[snowdog61]

Well I'm one who is always open to learning but from what I know (maybe 'thought I knew' is a more accurate statement), the original 300 bar valves won't take a yoke and are non-dimpled. The 230 & 200 bar valves will take the insert and seat at the correct depth to allow a yoke set to be used - the 200 & 230 bar having a much shallower thread depth. I'll assume they should have the yoke dimple on the back to register the yoke retaining screw. I have never seen a 300 bar valve with a dimple and I see no reason why a manufacturer would add an extra machining step to 300 bar valve as they were not intended to be anything but DIN. I do know there were vendors (not sure who the actual manufacturer was) who offered the 7/8-14 NF thread form valves to allow doubling the tanks ( LH & RH valves which could of course be broken apart, plugged, and dove as singles) so there is really no doubt that they could have been set up with the doubles manifold in a non 300 bar flavor at the LDS. Finding those manifold valves seems to be the issue as no one I know of is currently manufacturing them - only the 300 bar version seems to be available in 7/8". I'm sure they are out there in parts bins and garages but nothing new. I looked but no joy which is why I switched to DIN, having 4 Worthington X7s (convertible) and 1 PST in the 3500 psi flavor (300 bar DIN). I got a great price on the PST but being ignorant I figured that I could just throw an insert in and go dive - DOH! What a surprise when the insert went past flush and the yoke wouldn't even go over it. Thus came the education.......