DIYbanter - O-ring tolerance

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O-ring tolerance

I'm making a part that has an O-ring in a seat. I.e., not in a groove.
The part will be "loose" most of the time & I want the O-ring to
remain in its seat by having the seat diameter smaller than the O-ring's
nominal diameter. I.e., it'll be squeezed into the seat. How much
smaller can the seat be? The O-ring's nominal diameter is 0.7 & its
thickness is 0.1

Thanks,
Bob

O-ring tolerance

On 19/07/17 20:07, Bob Engelhardt wrote:
I'm making a part that has an O-ring in a seat. I.e., not in a
groove. The part will be "loose" most of the time & I want the O-ring
to remain in its seat by having the seat diameter smaller than the
O-ring's nominal diameter. I.e., it'll be squeezed into the seat.
How much smaller can the seat be? The O-ring's nominal diameter is
0.7 & its thickness is 0.1

Thanks,
Bob

With O rings I think the standard bible for applications is the Parker O
ring design guide which is easy to find online.

O-ring tolerance

https://www.parker.com/literature/OR...g_Handbook.pdf

Chapter 9 has the sizes and tolerances

O-ring tolerance

"Bob Engelhardt" wrote in message ...

I'm making a part that has an O-ring in a seat. I.e., not in a groove.
The part will be "loose" most of the time & I want the O-ring to
remain in its seat by having the seat diameter smaller than the O-ring's
nominal diameter. I.e., it'll be squeezed into the seat. How much
smaller can the seat be? The O-ring's nominal diameter is 0.7 & its
thickness is 0.1

Thanks,
Bob
================================================== ========

Orings are not compressible so the cross-sectional area of the groove while
sealed must be at least as large as the cross-sectional area of the oring.
Usually the groove depth is made 75-85% of the oring diameter to give 15-25%
crush for sealing. For really demanding designs Parker has tables of
different groove shapes for different oring materials used at different
pressures, but for normal not-really-critical stuff 80% works. Of course,
that wide groove lets the oring fall out when not sealed :-). The best
answer for that is a dovetail shaped groove with the top width a little less
than the oring diameter. The narrow top keeps the oring in place on
disassembly and the extra width at the bottom of the groove keeps the oring
from being extruded or cut.

--
Regards,
Carl Ijames

O-ring tolerance

On 19/07/17 21:37, Carl Ijames wrote:
"Bob Engelhardt" wrote in message ...

I'm making a part that has an O-ring in a seat. I.e., not in a groove.
The part will be "loose" most of the time & I want the O-ring to
remain in its seat by having the seat diameter smaller than the O-ring's
nominal diameter. I.e., it'll be squeezed into the seat. How much
smaller can the seat be? The O-ring's nominal diameter is 0.7 & its
thickness is 0.1

Thanks,
Bob
================================================== ========

Orings are not compressible so the cross-sectional area of the groove while
sealed must be at least as large as the cross-sectional area of the oring.
Usually the groove depth is made 75-85% of the oring diameter to give 15-25%
crush for sealing. For really demanding designs Parker has tables of
different groove shapes for different oring materials used at different
pressures, but for normal not-really-critical stuff 80% works. Of course,
that wide groove lets the oring fall out when not sealed :-). The best
answer for that is a dovetail shaped groove with the top width a little less
than the oring diameter. The narrow top keeps the oring in place on
disassembly and the extra width at the bottom of the groove keeps the oring
from being extruded or cut.

For really demanding applications anti extrusion rings are available to
support the O ring and prevent it being nipped, I think the details are
in the Parker manual, certainly a mate that worked in truck air brake
systems was very familiar with the details of their use.

O-ring tolerance

Thanks for the replies.

I got the Parker book and couldn't find the "style" that I want to use:
an O-ring in the bottom of a well, with a cylinder pressing on it. As:

||_______||
|O_______O|

I thought that I had seen such a use, but maybe not.

Not that it matters, cause I don't really have any flexibility as far as
the sizes go. So, I'm going to make it and see what happens. I'll let
you know.

O-ring tolerance

On 7/21/2017 5:53 PM, Bob Engelhardt wrote:
Thanks for the replies.

I got the Parker book and couldn't find the "style" that I want to
use: an O-ring in the bottom of a well, with a cylinder pressing on
it. As:

||_______||
|O_______O|

I thought that I had seen such a use, but maybe not.

Not that it matters, cause I don't really have any flexibility as far
as the sizes go. So, I'm going to make it and see what happens. I'll
let you know.

Can you machine a groove just over half the thickness (deep) of the
o-ring in the bottom of the well? Make it tight to retain the o-ring and
leave enough protruding to seal .

--

Snag

O-ring tolerance

On 7/23/2017 8:23 AM, Terry Coombs wrote:
On 7/21/2017 5:53 PM, Bob Engelhardt wrote:
Thanks for the replies.

I got the Parker book and couldn't find the "style" that I want to
use: an O-ring in the bottom of a well, with a cylinder pressing on
it. As:

||_______||
|O_______O|

I thought that I had seen such a use, but maybe not.

Not that it matters, cause I don't really have any flexibility as far
as the sizes go. So, I'm going to make it and see what happens. I'll
let you know.

Can you machine a groove just over half the thickness (deep) of the
o-ring in the bottom of the well? Make it tight to retain the o-ring and
leave enough protruding to seal .

I probably could have made a groove, but I didn't need to. The diameter
of the well had to be the same as the fitted cylinder (0.71) and the
closest O-ring was 0.74, or so. That .030 squeeze holds it nicely.

It also seals nicely, holding 900 psi of CO2.