A wierd thing happened at the dive shop today . . .

[Big Deal]

I had just bought a used deco bottle that had a recently serviced valve on it. The bottle had a born on date of 99 and the vavle was a thermo, three digit serial number (no E) with a "nitrox use only" tab and a green knob. I took it into a shop to have it filled with 50%. Here is the odd part:

When the bottle was hooked up to the fill whip and the valve on the whip was opened first, and the bottle opened second, there was no movement of air (the pressure gauge held steady). However, if the bottle's valve was opened first, and the whip was opened second, the air moved from the higher pressure filling bottle into the deco bottle. For those wondering the valve turns smoothly in both directions. The stem was moving along with the nut in both directions. When not connected to the fill station, the valve operated normally (i.e. as the valve was turned on, small amounts of air followed by more as the valve was turned).

I suspect many of you will suggest I invest in a newer valve. I agree. However, I've gone through physics of this and thought through the valve components (did a few internet searches) and I can't figure out why the stem turns but the valve won’t open up when the external pressure is greater than the internal pressure.

Anyone had a similar experience. Thoughts?

[boydski]

I would suggest disassembling the valve and inspecting the plug (2,3) and stem (8). If the stem is not seated well on top of the valve plug (i.e. not aligned correctly), it may behave as described. Re-build the valve with new parts (readily available) if they are worn/damaged.



Good Luck,

[rcontrera]

The only way for that valve to act like it did is for the soft seat in the valve to have come loose from the body (2,3) so that it could be held on the seat by the body when closed or fill whip pressure in the open position or moved off the seat by bottle pressure.

Other than that, it is just plain magic!!

[kdupreez]

like Ray said, the valve nylon seat probably came loose and the external pressure is keeping it sealed.

in that picture no 2 and 3 are the high pressure seat nut (2) and actual nylon seat (3).. it comes as a single unit, but they could potentially seperate and then what you describe will happen when the high external pressure gets between the nut (2) and seat (3) and then keeps the seat (3) firmly planted on there.

you can buy the 2+3 asemblies as units, but i would suggest just buy the entire rebuild kit for $10 and rebuild it..

http://northeastscubasupply.com/store/i ... ct_id=6854

(Make sure of your valve manufaturer though.. not all kits fits all valves)

K

[camerone]

you can buy the 2+3 asemblies as units, but i would suggest just buy the entire rebuild kit for $10 and rebuild it..

IIRC, the kits do not come with a new burst disk assembly, so you'll need one of those, too, which you order separately. Not strictly required if you're rebuilding the valve, but to me, it's a convenient time to change it out for a fresh one since you're going through the trouble of making the valve perfect again.

Unless they fail sooner, I usually just rebuild valves when I hydro the cylinders...

-c

[rcontrera]

Unless they fail sooner, I usually just rebuild valves when I hydro the cylinders...

Man ... I wish more people were like you! Way back in the stone age when my wife had a dive shop, I always recommended that to the customers and they always thought I was trying to rip them off. Or we would get that guy that would bring in a tank with a valve that you can hardly turn the knob and he would scream that "It never did that before you guys did the VIP!!"

While it is a tough little piece of metal, the valve is probably the weakest link. If you think about it, that little seal has 3000 psi of air on one side of it, and salt water on the other side. And we pay less attention to it than anything else we dive with.

[CaptnJack]

And burst disks are ONLY installed at about 8 ft/lbs which is a surprisingly light touch.

[Waynne Fowler]

Unless they fail sooner, I usually just rebuild valves when I hydro the cylinders...

Man ... I wish more people were like you! Way back in the stone age when my wife had a dive shop, I always recommended that to the customers and they always thought I was trying to rip them off. Or we would get that guy that would bring in a tank with a valve that you can hardly turn the knob and he would scream that "It never did that before you guys did the VIP!!"

While it is a tough little piece of metal, the valve is probably the weakest link. If you think about it, that little seal has 3000 psi of air on one side of it, and salt water on the other side. And we pay less attention to it than anything else we dive with.

Im with you. Rebuild it at vip intervals and burst disks at hydro...