Some Assmebly Required

[SpyderTek]

Ok bought my first tank today...Since I bought it in the store and not online / shipped to me I was a little surprised to find that the valve was seperate. (Read: Not assemebled with the tank)

So here is my question....How tight does the valve have to be? Do I just screw it in with my hand? Or should I wait till I get my first fill and have them put the valve in then?

I realized I could have asked them to assemble it before I left the store with it, but I didnt think of that till I was already half way home.

Thanks for any info

SpyderTek

PS> It is a standard AL80 tank with a Sherwood K-valve.

 

[trymixdiver]

Good question

I would think hand tight is fine. Maybe someone will enlighten us both.

Andy

 

[devjr]

Snug it up a bit with a wrench. Wrist tight, no muscle.

 

[Walter]

You don't need a wrench. Your best bet is to take it back to the dive shop. Have them put on the valve and fill the tank. A fill should come with the purchase and you need some pressure to keep moisture out.

 

[Campana]

Walter is right, of course. But, putting a valve on a tank is no big deal. You need a small amount of silicon or some Crystalube (if you ever are going to use it for nitrox, don't put any silicon on there because you'll be cleaning it off later). Make sure the threads on tank and valve are very clean. Put the silicon or Crystalube on the threads and on the large oring on the bottom of the valve. Don't gloop it on, just a very light coating-you shouldn't see any globs anywhere. Start the threads very carefully, and then just screw it on. I do hand tight, as tight as I can get it with my hand, then a little bump with a wrench. I have seen a lot of shop persons tap the valve with a hammer, just a light bump, but I don't feel that is necessary or desirable. The whole process sould feel pretty smooth. If you get any binding, don't keep turning and don't use a wrench to force it past any binding, cause you might bung up the threads.

Get the tank filled asap, cause the dry scuba air in the tank will help prevent any corrosion from building up.

They should have filled the tank for you at the shop, by the way.

Dave

 

[neil]

If you bought it at a shop it should have come valve-on, visually inspected and filled. Take it back and whine loudly.

Neil

PS the official torque setting is: kung-fu tight by hand.

 

[The Chairman]

Check the manufacturer...

Luxfer recommends 50 ftlbs for all of it's 3/4" valves.
PST recommends 75 ftlbs for all of it's 7/8" valves.

These values were taken from the PSI Inspecting Cylinders manual and the internet.

Personally, I tighten them with a crescent wrench until I feel the valve seat metal to metal.

DO NOT try and tighten valves by pounding on the knob. That will ultimately BEND the valve shaft and will lead to leaks.

 

[roakey]

Originally posted by NetDoc
Luxfer recommends 50 ftlbs for all of it's 3/4" valves.
PST recommends 75 ftlbs for all of it's 7/8" valves.

Both the PSI class and workbook go into this better than the book; though 75 foot pounds is correct for the tapered threads, for straight thread valves (the only kind you'll encounter unless you have a antique 72 for example) the “standards” are all over the board. The problem is that the cylinder manufacturers have specs, the valve manufacturers have specs (so whose spec do you use?) and they're all more or less [incorrectly] based on the tapered valve spec.

Bottom line from the PSI class for straight thread valves: As hand and tight as you can get it (kung-fu tight is a good description ).

From the July 2001 PSI class workbook, page 36, step 6b of the inspection protocol:

“The heel of your hand provides enough force to release a 3/4" straight thread valve. DO NOT STRIKE VALVE hand-wheel or reserve mechanism repeatedly to loosen.”

If you can loosen a valve torqued to 50 ft-lbs. with the heel of your hand, you can make a few bucks for sure in those ultimate fighting championships.

The workbook falls down when it comes to a tightening spec, page 38, step 14a:

“Do not overly tighten O-ring sealed valves.”

Gee, that's helpful, not, but rest assured that during the class it is made excruciatingly clear that straight thread valves are tightened only hand-tight.

Roak

Ps. The shop should have put it together for you AND given you a fill.

 

[The Chairman]

His theory was that when the valve seats "metal to metal" then just stop. If you are using a crescent wrench on the valve, then when the metal body of the valve "touches" the tank, you hear a low resonant chime... almost like you thumped the side of the tank with the wooden handle of a hammer. I can not loosen this by merely thumping the valve knob.

BTW, tanks do not ship from the factory with an EOI (Evidence of Inspection) sticker, so make sure your shop deals with that as well.

 

[devjr]

Netdoc has it right, the valve has to be lightly wrenched and it must be metal to metal. Where are you guys coming from with all this hammer, kung fu and junk? And what about 75 ft lbs to tighten a tapered valve? That is OK for a compressor head bolt or such, but tightening a 1/2" tapered valve usually requires an 18 inch monkey wrench and substantial body weight. You tighten until it seals or will turn no farther, period. A chain vise is required to secure the tank.

There are two types of seal used with diving cylinders which employ O rings. The Aluminum and other medium pressure tanks use a compression O ring that must be fully captured. The HP steel tanks use a friction fit O ring which, although it theoretically could seal with hand tighening, I wouldn't recommend it.