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Tank Valve Tightness??

Posted: Tue Aug 15, 2006 5:15 pm
by diver-dad
I got an Al 80 off of a (formerly diving) neighbor of mine and because it had not been used for several years, brought it in for a hydro, visual, & rebuild of the valve.

It was totally depressurized (and had been for years).

What surprized me was when the guy at the shop just smartly popped the valve handle with his palm which unseated the valve body and he then started unscrewing the valve body from the cylinder.

??? Are they supposed to be just "hand tight??" I know they have the o-ring to seal them but I would have thought that there should have been more torque applied when tightening the valve onto the cylinder.

I guess my second question is: should there be any lubricant applied to the threads before reassembly. (assuming use with just air, no EAN.)

Anyone have any info on that?? :book:


Posted: Tue Aug 15, 2006 5:25 pm
by Tangfish
The tank valves don't have to be put on tremendously tight, since once the tank is pressurized all of the threads will be pushed outward. You can put a small bit of lubricant on the outward threads to help ease it back on. If you ever plan to use Nitrox you should use the appropriate lube. I only know what I know from swapping out my tanks from singles to doubles. Hope that helps.

Posted: Tue Aug 15, 2006 7:31 pm
by rcontrera
CT is absolutely right! The valve just has to be screwed in to the point that it "kisses" the tank. That insures that the O-ring is captured. Once pressure is applied, the o-ring is pressed into the sealing area of the valve and tank and "locks" them together.

Dive shops used to use a small rubber hammer to tap the valve in just beyond hand tight so that it didn't accidentally unscrew while the diver was carrying it back to the car after a dive.

However, valves were designed to be smacked a bit while some aren't anymore.
Image You will notice a spring and plate on the end of the valve stem that holds the handle on. That spring allowed for a light tap to seat or unseat the valve without doing any damage to the valve stem itself. The handle would just lay over and all the force was on the body of the valve.

However, Genesis, in all it's wisdom, decided it would be cheaper to remove the spring and mounting nut and mold a metal base into their handles so that they could just use a cheap corrosion resistant nut off the shelf.

Now, that in itself is not a problem for an old timer like me. But there are a lot of young pups in dive shops now that have a hard time identifying the working end of a rubber mallet, let alone types of valve handles. So, a decree from on high has come down to say "Thou shalt never whack your knob!" [-X (hmmm ... I better leave that alone!)

So, all that said, your guy did fine by my book, but the fanatics would say that he should have used a wide jaw wrench across the face of the valve or on the valve body flats.

Oh, and as far as lubricant is concerned, if ANY salt water were to get into the threads (usually from a wet fill), your valve will freeze in place from corrosion. It is best to lubricate down to just about the last thread but never into the cylinder and, hopefully, you won't have that problem.

Posted: Tue Aug 15, 2006 7:49 pm
by DiverDown
Thanks for the in-depth description of the tank valve removal Ray. Usually when I smack my valve with a rubber hammer I wind up bending my pin.. ](*,) Luckily for me its at my LDS and parts a readily available :supz:

Posted: Tue Aug 15, 2006 9:57 pm
by diver-dad
CT & rcontrera -

Great explanation & I appreciate the exploded view - learn somethin' new every day!

Makes sense.


Posted: Tue Aug 15, 2006 11:19 pm
by Tangfish
Good stuff Ray, thanks for kicking down the knowledge! :book:

Posted: Wed Aug 16, 2006 12:18 pm
by CaptnJack
PSI recommends lubing all threads with Dow Corning 111 (a high quality silicon) on all air cylinders. Cristolube on nitrox cylinders. There's no drawbacks to lubing the threads and plenty of bimetallic corrosion frustration waiting if you don't.

Use a wrench to loosen, not the knob. Hand tight is fine.