What gasket material should I use?

I've designed a flow cell made up of 2 pieces of plexiglas with fluid
flowing in between. The top and bottom pieces are separated by a gasket
and pressed together by fasteners. The thickness of the gasket therefore
defines the depth of the flow channel. I would like to vary the
thickness from 0.5 mm to 2mm (after compression) by using gaskets of
different thickness. When fluid is flowing through the flow cell,
depending on the flow velocity, the internal pressure can vary from 0 to
5 atmosphere. Right now, I'm sourcing for a suitable gasket material.
Apart from the main criterion that it mustn't leak, it is also
imperative that its thickness be relatively constant after a certain
compressive stress. This requirement is necessary as the fasteners are
hand tightened and so compression forces can vary by quite alot.
Finally, the material should resists acids and alkalies. What would you
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A redesign so o-rings are used to seal and appropriate shim stock is used to effectively control the spacing. ________________________________________________________ Ed Ruf Lifetime AMA# 344007 ( snipped-for-privacy@EdwardG.Ruf.com)
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Ed Ruf
What he said
Brian W
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Brian Whatcott
I don't think that o-rings would necessarily be the solution, based on the configuration of the flow cell you have described. But using shims, or spacers, to control the thickness is certainly the best chance you have for success. There are a number of closed-cell foam gasket materials that can perform the sealing. But you can't control their compressed thickness. So use a gasket and spacers.
Kevin Alexeff
Reply to
Kevin Alexeff
yep. I will go with gasket and spacers. One more question. Because the flow thro' device is quite small (60mm x 90mm), I had to restrict the width of the gasket. Is there a good way of estimating the minimum "no leak" width?
thanks philip
Reply to
Dear Philip:
In general, the pressure at the contact point of your gasket with your surface will have to exceed the pressure to be contained.
There are plexiglass-to-plexiglass (or other-to-plexiglass) sealing methods, but usually involve pipe threads. The sealing "width" is very small... less than 1 mm usually (even if threads are very long in the high-pressure-to-low-pressure axis).
If you design around o-rings, you will likely be limited to the smallest commonly available cross section, namely 0.070 inch. A PTFE encapsulated EPDM o-ring is not very flexible to surround an odd shape, but will take anything you can throw at it. Usually lasting longer than the plexiglass.
You might consider cutting a groove on the *outsides* of the plexiglass, and let the internal pressure seal on the gasket.
The biggest problem with a thin gasket is making it. Then handling it. Then keeping it from buckling in installation. Then keeping it from eroding.
David A. Smith
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