Help with O-Ring Groove Design (Static Radial) 1

[spazzyfry123]

Hello all.

I'm finishing up a design that will be utilizing an O-ring for sealing the OD of a spacer to the ID of a bearing support housing. This will be the final seal point for oil within the gearbox along with rotary seals at the ID of the spacer to seal to the spinning shaft. The last bit that I am unsure of is relative to the O-ring groove (gland) dimensions...specifically the diametrical clearance.

Unfortunately this is a retro-fit type job and with the space constraints within the design area, I am left with needing to have a press fit between the spacer and the bearing housing to prevent the spacer from potentially backing out of the housing.

With this known, is this diametrical clearance absolutely necessary with very low pressure? I would like to have a press fit across the face of the OD of the spacer. The clearances given within the Machinery's Handbook are valid up to 1500 psi. My specific application will see ~7 psi at the most as I have relief valves on the gearbox.

However, if this diametric clearance is necessary, I would assume it will be needed from the direction of oil flow (Shown marked in red) until some distance past the groove width for the O-ring. My question: How far past the groove width is this required? (Shown marked in blue)

I have attached a few snap-shots to help get a visual across.
The blueish, purple is representative of the spacer mentioned above.
The black is the O-ring - AS568A-438 A70 Durometer rating.
The component that the OD of the spacer is mating to is the bearing housing.

Thanks for your help!
-T

 

[dgallup]

That gives a stretch of 3.8% and an uncorrected squeeze of 20%. Actual squeeze will be a little less due to the change in cross section due to stretch. Those numbers look pretty good to me.

So far nothing has been said about the o-ring material selection but that is every bit as critical as the dimensions. Make sure your material is compatible with the applications oil, temperature range and other environmental considerations.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[tbuelna]

spazzyfry123-

It seems like you're still a bit confused on the design approach discussed, so I've attached a sketch that may help clear up the issues involved. I would agree with dgallup that the gland dimensions in your last post seem good for a 2-259 o-ring sealing low pressure. However, you still need to address the problem of an insufficient housing bore edge chamfer.

Also, as dgallup suggested, it would be wise to spend some time studying the sections in the Parker O-Ring Handbook covering issues like chemical compatibility, temperature limits, compression set, etc of o-ring elastomer compounds.

Hope that helps.
Terry

 

[spazzyfry123]

I must have overlooked that info; I had thought I mentioned both points previously.

The specific O-ring chosen (Buna-N for oil applications) is

http://www.mcmaster.com/#9452k359/=ry4pmr

In regards to the chamfer, as mentioned above, a 15° chamfer with an OD of Ø172 seemed to be the ticket. Are we suggesting that this is not enough OD?

Thanks for everyone's help.