Changing Scuba Tank Valve

[halocline]

The tank neck o-ring should not be lubed, as Vance mentioned. Dry-rot on EPDM, nitrile, or viton o-rings would simply not ocurr in anywhere near the time between hydro testings, let alone visuals. The threads should be lubed a bit to prevent galvanic action, especially with AL tanks. I can't imagine tightening a tank valve to 50 ft lbs. That's really tight and I have no idea what could possibly be gained from it. The seal is made by the o-ring, and IMHO the less stress that's on the tank neck threads, the better. Especially considering you'll remove that valve and replace it at least 20 times during the life of the tank, if you inspect annually and the tank is used for a 'normal' life span. (whatever that is....)

 

[Doc Harry]

The only B.S. is yours.

Valve and thread data are determined by the manufacturer based on their research.

Where is your research to prove that the manufacturer is wrong? Sorry, I'm going to follow manufacturer specs, not some cowboy shooting from the hip.

Speaking from personal experience, tapping a valve with a rubber mallet can and does cause the deformites of the valve orifice and stem parts. That's why I don't do it anymore.

Doc.. you're textbook correct, but mostly BS.

If the tank has pressure in it, that valve isn't coming off, at least not easily. Also, as far at torquing it on, it's BS too. Text book correct but 500-to-3K of pressure will hold it in place.

A rubber mallet isn't going to do any harm as long as it moves with gentle tapping. If not, use a wrench.

...I can't imagine tightening a tank valve to 50 ft lbs. That's really tight and I have no idea what could possibly be gained from it. The seal is made by the o-ring, and IMHO the less stress that's on the tank neck threads, the better. Especially considering you'll remove that valve and replace it at least 20 times during the life of the tank, if you inspect annually and the tank is used for a 'normal' life span. (whatever that is....)

Again... show me your data that proves the cylinder manufacturer is wrong. Show me your data that proves the manufacturer specs cause harm.

Show me. Show us all. We're waiting.

 

[Krazytomdiver]

As a dive guide,a hammer & dive equipment go together like my Ex-wife & me. I use a 'cheater bar' on my giant tank wrench while being very careful not to round off to soft metal neck. Sometimes soaking in white vingar or vesco (hull cleaner) for days just to break it free. Between the brass parts,nylon rings,and silicone seals; I would never beat on anything. Parts are too hard to find when you are miles from no where. Re-assemble with a rebuild kit if available,clean with white vingar, and light lubrication as required.

"living life without a hard bottom"
KT

 

[knowone]

Get rid of the paint and crud and rust from the top of the neck
and cone, had I just landed in the land of ninnies and boobies

Valving of SCUBA (Air) Cylinders

Valve installation torque values for Luxfer aluminum alloy cylinders and liners - Luxfer: Setting The Standard Worldwide

What some BS manufacturers said

YouTube - Scuba Tank - Valve Cut

and then some

nanu nanu

and just for expedition for the busy ones, there's some knob malleting in there

and for those that are restricted, only by what they know and do, well oop dad as

 

[Couv]

In addition to the excellent advice you've received so far, please ensure the burst disc on the new valve is correct. ( usually 5/3 the working pressure of the tank. )

 

[Hatul]

The general feeling (though it is far from unaminous) is that the neck O-ring should NOT be lubed, since it is static and doesn't need lubing, and anyhow is not really acting as an O-ring at all but rather as a crush seal. Lube will just encourage it to extrude.

The threads, though, should be lightly lubed, with an appropriate lube, silicone or oxy-compatible depending on what the tank will see, as a dielectric barrier to prevent dissimilar metal corrosion between the valve threads and the tank threads. This is especially important with aluminum tanks.

Can I ask you, what's the difference between a crush seal and an O ring?

Adam

 

[spectrum]

An O-ring is the part.

A crush seal is the type of seal it forms in this application.

The same O ring can be used in a dynamic moving application for instance.

Pete

 

[Hatul]

An O-ring is the part.

A crush seal is the type of seal it forms in this application.

The same O ring can be used in a dynamic moving application for instance.

Pete

Hi Pete, I looked this up for more details, and as I understand it, in a crush seal the O ring is forced into a triangular cross section to make a static seal.

Normally the O ring maintains it's round cross section and is pushed against the seat by the pressure, such that the external pressure on the O ring is always less than the pressure of the O ring against its seat.

Adam

 

[halocline]

Again... show me your data that proves the cylinder manufacturer is wrong. Show me your data that proves the manufacturer specs cause harm.

Show me. Show us all. We're waiting.

Relax, and I certainly never said anything about "data", or "proving the manufacturer specs cause harm". All I said was that I can't imagine tightening a straight o-ring sealed tank valve to 50ft lbs. Not that I've done hundreds, but I've done dozens and have never tightened even close to 50 ft lbs, and I've never had any sort of leak or extrusion problem, and likewise I've never had any problem getting the valve off later. BTW, the luxfer site says that "the goal of the installation process is to install the valve with the least amount of torque or tightness that will make a seal..." and mentions that the maximum torque...not recommended torque...is 50 ftlbs. I realize that's for AL tanks. But what's the advantage of that much torque for steel cylinders, if tightening to a lower torque provides a seal?

 

[aquaregia]

If you're paranoid, yank the burst disc before taking off the valve. Has the added side effect of preventing you from using that spare valve with a 5k5 burst disc on a steel 72 (or the reverse) just because you had it lying around and didn't bother to check the disc.