Tank o-ring "grooves"

[DepthCharge]

In most applications an O-ring groove is a square sided groove. Does anyone know why on a scuba tank the neck O-ring is cup shaped?

 

[maged_mmh]

coz it doesn't require lubrication. square shaped groves are to accommodate lubricants film layer between O ring & its groove

 

[ClayJar]

Actually, at least on Luxfer aluminum cylinders, the tank neck O-ring fits in a square cross section channel. (In fact, there's even a tool to clean and polish it if you get corrosion there.)

 

[maged_mmh]

Actually, at least on Luxfer aluminum cylinders, the tank neck O-ring fits in a square cross section channel. (In fact, there's even a tool to clean and polish it if you get corrosion there.)

as you said it, it'll promote corrosion. I cannot see a reason why they had adopted such design; all you need for an air tight is a circular groove to seat the O ring snugly

 

[fppf]

Oring grooves do not need to be square. Square grooves are just the easiest to machine and are most common.

Different mfgrs have differnt groove shapes.

Depending on the tank, the valve interface to tank "Groove" ends up being a triangle, or square, or other shape. As long as the cross section will generate the correct amount of squeeze and the gap between parts is maintaned to prevent extrusion the groove shape is not that critical. Typically oring lubercation is not held by the groove.

 

[ClayJar]

as you said it, it'll promote corrosion.

I certainly neither said nor intended to imply that it would promote corrosion. In fact, in all the cylinders I've inspected, not once has the sealing surface shown signs of wear. Sure, there's a tool for polishing it back to pristine condition, but I've never needed to even think about ordering one as of yet.

I cannot see a reason why they had adopted such design; all you need for an air tight is a circular groove to seat the O ring snugly

Luxfer's O-ring sealing surfaces are easy to machine. They seal well. They're almost trivial to machine back to pristine condition with little more than a drill and an inexpensive resurfacing tool. I can't see a good reason why you wouldn't use such a design, at least in a cylinder with the characteristics and design specs (pressure, etc) of an aluminum cylinder.

 

[maged_mmh]

which one of these do you think has better surface contact?

 

[ClayJar]

which one of these do you think has better surface contact?

There is not enough information to arrive at a supportable conclusion.

 

[DepthCharge]

Actually, at least on Luxfer aluminum cylinders, the tank neck O-ring fits in a square cross section channel. (In fact, there's even a tool to clean and polish it if you get corrosion there.)

HMMMMMMMMMMMM.......my 40 cft luxfer has the cone shape........2002 manf date

 

[fppf]

Maged
Your thinking of an Oring like a solid.
You need to think of an Oring as a liquid with a really really high surface tension. The way an oring seals is by flowing into the joint. The surface tension keeps it from extruding through any gaps between the parts. The clearence between parts is a function of pressure and the surface tension of the oring. The higher the pressure or softer the ring the tighter the parts must fit.

I recommend reading Parkers Oring design guide. There is a lot of good info and they do a good job of reviewing the basics.