O-ring Groove Design

Please 'splain to me the reason for an O-ring groove that has clearance on the sides. (3/16 wide for 1/8" ring)

I have two to produce currently for my own app, and not 100% sure that I want to copy the design or not.

My app here has some sliding action, probably 1/4-3/8", and it will spin enough to reposition, but that is it. Talking to a buddy - he was wondering if they actually wanted to induce some roll during the slide - to possibly reduce creating a flat spot. ???

Pretty sure that at least one of these has no real pressure on it, and I believe the second might be the same as well.

I believe that I have produced other out-of-square grooves over the years, but then I don't know the ring they were puting in those grooves. But this app here just has a basic O-ring in it. There is a slight possibility that it could have had a quad type in it at one time, but I doubt it.



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Think Snow Eh!
Ox

All things o-ring are enumerated here.
https://www.parker.com/literature/ORD 5700 Parker_O-Ring_Handbook.pdf

You can also get special form tools for forming the trapezoidal grooves.

Not sure exactly what you are talking about, but O-rings are supposed to compress into the groove, so the groove has to be big enough to accommodate that.

As previously pointed out the Parker handbook has pretty much everything you want to konw about o-rings in it.

Commonly designed static and dynamic glands have different dimensions and many low pressure dynamic seals are intentionally wider than the o-ring when compressed. This is to allow the o-ring to have some rotation during the start of motion when reversing direction. This reduces the breakaway force to start the system moving and makes it smoother to start.

Also if diametrical clearances are large or pressures are high then you can also use a soft o-ring with a hard backup to prevent extrusion. This obviously requires a larger gland width as well

Ivan

It just occurred to me that I haven't seen my paper version in years.
I wonder if you can still buy one.

An o-ring seal is pressure activated. There needs to be space on one side so that oil pressure can force the rubber into the

joint. This way, the higher the oil pressure, the tighter it seals.

As opposed to a gasket type joint, where the higher the pressure, the more it leaks.

Ox, was this intended for use with a backup ring (or two) in addition to the O-ring? If not, I share your caution about reproducing the design willy-nilly, because "clearance" isn't any sort of common practice for O-rings.

The lubrication of the O-ring is necessary to extend it's wear life. The wider slot allows the lubricated side of the ring to roll into contact with the cylinder wall. An O-ring in a dynamic application is not particularly long lived anyways if the pressure is high, or, there is no lube. So the roll effect is about the only thing that can be done with an O-ring to lengthen its service life.

A 1/8 oring measures .139.

Grove width= .189 +/-.005

Depth.111-.113 radial

Depth .101-.107 axial

Diametrical clearance .006 max.

Static

For reciprocating

Grove depth.121-.123

sfriedberg said:

Ox, was this intended for use with a backup ring (or two) in addition to the O-ring?

Click to expand...

No, and I found that there is another OD ring with the same boundaries.

HuFlungDung said:

The lubrication of the O-ring is necessary to extend it's wear life. The wider slot allows the lubricated side of the ring to roll into contact with the cylinder wall. An O-ring in a dynamic application is not particularly long lived anyways if the pressure is high, or, there is no lube. So the roll effect is about the only thing that can be done with an O-ring to lengthen its service life.

Click to expand...

I like that explanation!
It could be complete BS, but I buy it!!!



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Think Snow Eh!
Ox

Heavey Metal nails it. In reality, the groove width has very little meaning if a static seal. If dynamic, it is more critical.