O – Rings, bit of help needed

This topic has 6 replies, 5 voices, and was last updated 12 December 2014 at 01:02 by Jon.

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26 March 2014 at 16:03 #148102
Oompa Lumpa
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@oompalumpa34302
So, my "Get-out-of-Jail-Free" card has expired. ie. I can't find the chap I normally call for advice with this is MIA and I suspect he left his present job and has gone elsewhere. No surprise really as he was very good. But that now leaves me with the problem that I have pretended would never arise: Which 'O' ring to use for a specific job. I throw myself at the mercy of the forum!

The problem: I have a piston (in brass for the sake of pedantry) which measures out at 29.5mm, the Bore is 30.5mm (Chrome). Which size 'O' ring do I use to create a seal? The piston is compressing air to approx 750psi and I would normally on something this diameter use two 'O' rings one right behind the other and a nylon skirt ring for smoothness.

I prefer to use Viton rings but now, as my contact has left, I have no reference. If someone could point me in the right direction for some specs. I would be grateful. Depth and width of groove are also quite critical.

Thank you,
graham.
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26 March 2014 at 16:03 #23221
Oompa Lumpa
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@oompalumpa34302
26 March 2014 at 16:17 #148105
David Jupp
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@davidjupp51506
James Walker web site offers a free 'O Ring Guide' covering materials, housings etc. Other manufacturers may also offer similar technical material.
26 March 2014 at 16:29 #148108
mick
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@mick65121
The ERIKS "O" ring calculator is very good, just select material, size etc and it does the rest, an online search for Eriks O rings, should bring it up
26 March 2014 at 19:19 #148117
Oompa Lumpa
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@oompalumpa34302
Took some finding but HERE is the calculator for anyone looking in future.

graham.
10 December 2014 at 22:54 #172175
Ian P
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@ianp
Has anyone actually used the Eriks online calculator successfully I wonder?

I need to design several O ring sealed joints and have just spent the last hour struggling to make sense of how it works. I am baffled as to how, once having saved a design (after registering and logging in etc) that design is reloaded to edit or print out.

I can find no instructions in how to use the calculator but I think there may be a clue to its failings in that the features of this free design calculator include the ability to SAVE designs. However nowhere do that say it can load designs!

I think I might be able to get the details and dimensions I want by writing down the various intermediate results and then entering them again on the keyboard when needed for the next step.

No wonder it took you a while to find it Graham, maybe they hide the results as well.

Ian P
12 December 2014 at 01:02 #172249
Jon
Participant
@jon
Just tried it, seems to work.

What you will find is if buy three o rings from three sources to a BS standard most likely they will actually measure different.
So what you have inputted will change when o rings come.

It would be quite usable if the link provided off the shelf o ring sizes rather than input size of parts only to find nothings remotely available. For this to work would have to input actual o ring size.

Very rarely I draw things out and tend to either compress the o/d or expand the bore or even both. Some try to tell you to create clearance on a piston bore so floats with minimal contact on I/d of bore, the pressure creates o ring to contract and expand to create the seal.
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