Leak test design for O-ring

[kamikazeCHIP]

I am trying to develope a test to verify that an O-ring is sufficiently sealing. The O-ring is used to keep WEG out of the electronics portion of the unit. The WEG is being used to cool the unit.

I want to test the unit by pressurizing with air instead of pumping WEG. I want to use air for producibitility/timely build reasons. Since air molocules are smaller than WEGs I'm assuming air will leak more. Therefore, I am trying to come up with an acceptable amount of air leak that will validate the O-ring will not leak with the use of WEG. Does anyone have any input or experience comparing air leaks to a liquid leak? Any input on the kinds of experiements I should perform? Thanks.

 

[Eltron]

I would say that if you have a leak then your seal is not working regardless of the media. Generally, I do a helium leak test with a helium sensor on all of my critical applications. If I sense any helium then I tighten/ replace/ redesign. Allowing a certain percentage of leak based on molecule size is asking for it unless you are designing active or passive transport membranes.

Dan

http://www.eltronresearch.com

Dan's Blog

 

[unclesyd]

I would normally use a He Leak detector as post above. That is no fun as we have 2 mass detectors, along with three portable ones. We also use H2 with or with N2 dilution.
I have used pressure decay on several large jobs.
Along with Freon leak detection, back when Freon wasn't a bad word.
Last but not least is bubble testing using a senestive fluid.
The links below will give you good cross section of what's out there.
The method you can use depends on the volume of the object to be tested, with required sensitivity required, The number of components to be tested.

http://www.ateq.com/

http://www.amgas.com/ltpage.htm

Depending on the number of components to be tested and if not high enough to justify there are people who rent some of these instruments.

 

[kamikazeCHIP]

Thanks for you responses.

I do not have much experience testing O-rings for leaks. I was assuming that Helium/Air would leak in this situation just because the molecules were small regardless of design.

Eltron - from what you are saying the helium and air should not leak past the O-ring if the design and torques are sufficient? I was not part of the design so I'm not sure if tolerances were used for a liquid application rather than a gaseous one. Does that matter? Is the only reason helium is used because a leak can be detected in air?

 

[monkeydog]

Many years ago, JPL wrote a report for "zero leakage" it has a process for converting gas leakage to liquid leakage.

Here is the link for the report;

http://ntrs.larc.nasa.gov/search.js...or-Name&Ns=Loaded-Date|1&N=0&No=20&Ntt=weiner

 

[Eltron]

Check the Parker O-ring Handbook as well. Other than chemical compatibility and permeation the fluid that you're sealing against on either side of the seal shouldn't matter. That's an oversimplification of course, but your o-ring should seal against air regardless or you're not on the road to happiness.

Dan

http://www.eltronresearch.com

Dan's Blog