Tank O-Ring size????

I'm going to Home Depot in a bit and want to pick up some spare tank o-rings. What size should I get? This is for a yoke valve.

This is probably a dumb question, but I looked online and couldn't find any definative answer....every vendor simply sells "tank o-rings" and doesn't say what size they are.

Check this link looks like size 14 is your oring?
http://www.reefscuba.com/o_rings.htm
Rick L

I'd be afraid those are not the required quality, hardness, or material you want to expose to 3000psi. I expect they are intended for plumbing use and less than 100psi.

awap once bubbled...
I'd be afraid those are not the required quality, hardness, or material you want to expose to 3000psi. I expect they are intended for plumbing use and less than 100psi.

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I'd be interested in finding this out for sure.

I bought a 10-pack for $1.36 and the main reason for them was to attach bolt snaps to my hoses. I figured if I was going to be buying o-rings anyhow, I might as well make them useable for something else.

awap once bubbled...
I'd be afraid those are not the required quality, hardness, or material you want to expose to 3000psi. I expect they are intended for plumbing use and less than 100psi.

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Most o-rings sold as "hardware" in the US are 70-durometer neoprene (AKA Buna-N) in the 2-xxx size series. This ring is suitable for almost all non-O2 use in scuba.

There are are occasionally a few ring materials that do "better" in a particular application, but the Buna-N will generally work. "Special" urethane or Viton rings of several different varieties are used to better tune some regs, but the Buna-N will normally function with less than a 15% variation in performance specs or a slightly reduced shelf and/or service life. Manufacturing variations in the glands will usually amount to this much or more.

BTW An o-ring gland is the groove and supporting structure used to retain the ring, which includes the clearance dimensions used in the construction of the joint. Big gaps in the gland are cheap to build and generally will hold less pressure. Expensive tight fits to prevent extrusion of the ring can be used to hold pressures well in excess of 60,000 psi in both static and dynamic joints, with the same 'hardware" o-ring. Gland tolerance design for a commercial part is a trade-off of cost of manufacture and pressure resistance.

FT

Fred,

Since are knowledgeable about o-rings, how about shedding some light on automotive applications.

Specifically, are there any differences in the green o-rings readily available in bulk for use in automotive air conditioning applications and the green o-rings used in SCUBA gear?

Also, what are the differences between O-ring types? (HBNR, Viton, etc.)

Most o-rings sold as "hardware" in the US are 70-durometer neoprene (AKA Buna-N) in the 2-xxx size series. This ring is suitable for almost all non-O2 use in scuba.

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Fred is right about the rings. Commonly available rings will do fine in the tank neck and valve. However, regarding the clearance issue he mentioned; Scubapro piston regs don't do well with Nitrile or Buna N. These may extrude, particularly when used in the piston. Scubapro requires rings with special compounds and hardness specs for their regulators.

There are two sizes commonly used for the valve to reg seal on a yoke valve tank, the 2-014 "thin" O-ring and the 2-112 "thick" O-ring. The thin is by far the most common, but anytime you find yourself having trouble getting a seal with a new O-ring there's a good chance you are using the wrong one.

The numbers used are the standard aerospace AS568 ones used by most industrial suppliers - often the 2- will be left off. Hardware and plumbing suppliers often use entirely different numbers.

While almost everyone use plain old 70 duro nitrile in this location, most gear manufacturers recommend using a harder urethane or 90 duro O-ring for the yoke seal since these rings are very prone to extrude. The harder rings are sold specifically for this purpose by better scuba suppliers, and are especially good idea when reliablilty is important (though you should probably be using DIN in those situations!). Cheap imported O-rings which are what you'll usually get from discount sources often are made with more fillers and oils in them, and may not last as long as good quality ones; you can save a lot of hassle by inspecting them frequently and replacing them routinely, before they can become a problem.

Cave Diver once bubbled...

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Also, what are the differences between O-ring types? (HBNR, Viton, etc.)

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Attached is a link to a chart describing the different material used for O rings and there application.

O Ring types

I agree with Hacker's comments. The only valve face ring that I will install on my SCUBA are the white rings sold by dive shops. These are very reliable, do not extrude and are resistant to UV and temp variation. I have never seen one of these crack and deteriorate like the black rings.

Edit: forgot to mention; the tank neck O ring for 3/4-14SPT valve that I use is #568-214,.984 X.139

I believe that the '568' is 'nitrile' and 214 is the size.

Pesky