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• # O ring calculations.

Discussion in 'Calculations' started by Bert, Apr 6, 2013.

1. ### BertMember

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I would like to design a counterpart for a pressure sensor. The pressure sensor is the black one and the counterpart is the gray one.
How can I find the dimension of the counterpart? In other words how can I find the X and Y dimensions? there is a O ring involved and I don't know how to handle O rings?

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3. ### kevin.koehlerMember

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Hi Bert, we can probably point you in the right direction. Throughout this post, I'm going to refer to the Apple Rubber website, but I am not affiliated with them.

Gland Design
The first thing you need to do is select a gland design. http://www.applerubber.com/src/pdf/Section4a.pdf
I infer that this is a static seal (ie. it is not moving/sliding like a piston). What you have shown looks like a radial seal. However, you'll probably want to look at the various seal designs. The typical radial seal has a groove on the internal part, however since I'm guessing this is an off-the-shelf pressure transducer, you don't want to be modifying it with a groove. If you're stuck on a radial seal, a good machine shop should be able to cut a groove in the hole of the "counterpart" which you are designing.

Another option would be to use an axial seal design. This would place the o-ring either under the nose of the o-ring down at the bottom of the hole, or up at the flange at the top of the pressure transducer. I would lean toward placing the o-ring at the bottom of the hole, if your design is amenable to this. In this way, assembly would be simple - just drop the o-ring in. You could probably get away without using the inner part of the gland since (i also infer) that your pressure is internal, and the pressure would only be pushing the o-ring outward.

The last one I'm going to mention is the "static crush seal." This one might involve modification of your transducer to bevel the edge to 45 degrees, so I'm not going to take this one any further.

O-ring Size
Now that you have selected a basic design, you should choose an o-ring size. http://www.applerubber.com/products/o-rings.cfm
There are standard sizes of o-rings in inch and metric sizes (AS568 and ISO 3601, respectively). You are free to make a design that does not use one of these standard o-rings, but for obvious reasons of availability and cost, I recommend you use one of the standard ones.

Gland Dimensions
Now that you have selected a gland design and o-ring size, you can find the specific gland dimensions. http://www.applerubber.com/seal-design-guide/seal-types-and-gland-design/src/tableb.pdf

Let's assume that you selected the static axial seal, using an AS568 -006 o-ring. Look in the column for "internal pressure, diameter A." Uh oh, they just have "**".
While this is true, it may be acceptable in your application of a pressure transducer. Notice that the "Dimension A" is generally .005" less than the OD for the .070" cross-section/width family, so I would apply that to the -006 o-ring also. The .006 o-ring has a .254" OD, so a .249" for Dimension A would be appropriate.

O-ring Material
The last thing is material. http://www.applerubber.com/chemical-compatibility-guide/
But I'm sure you can figure this one out.

So I made a few assumptions along the way that steered us into an "uh-oh" situation. And we have something that seems like a reasonable recovery. Your particular design path might differ from this, but it at least will give you an idea of how to start. If you want more help, it might be good to provide a little more info on the size and intended use of this device.

Best regards,
Kevin

Last edited: Apr 7, 2013

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5. ### proinwvMember

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o-ring

The advice given you is correct. I have used the Parker literature for years and have found it reliable.

6. ### SkyNew Member

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Parker static O ring spec

Hi, I used parker too. It's very reliable.

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8. ### BertMember

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Thanks a lot for all the anwsers.
Best regards.

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10. ### pepsiozNew Member

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I use this site also, but will checkout parkers handbook now, good to have a backup to double check before cutting

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