Posted by Diffusion in Polymers on December 14, 2004 at 10:40:16:

In Reply to: how to test permeability of o-rings posted by Maxime Belanger on December 13, 2004 at 22:42:22:

Dear Maxime Belanger,

First the Helium and O-rings. we have obtained and calculated the permeability (diffusivity and solubility) of Helium in most commonly used O-rings. As Helium is a small and "quick" molecule, the diffusion rate / diffusion coefficient of Helium in the O-ring is sometimes used as a "worst case" measure for all other molecules.

However, in case of Hydrofluorcarbons HFC refrigerant, chemical formula CH2FCF3, this is not expected to be very helpful.

Although the initial diffusion coefficient may be quite low, the solubility will be relative high (for example in VITON), this may give a larger permeability than Helium (while permeability=diffusion rate x solubility).

Depending on the liquid or gas state of the Hydrofluorcarbons HFC refrigerant, a different experimental/calculation approach* has to be chosen. Do not hesitate to contact us via j.s.van.der.wal@gmail.com to obtain further support and advice.

Thanks.

Best Regards,

*Based on the library and expertise of diffusion-polymers.com it is expected that major part of this case can be calculated.

: I am interested in gathering permeability data of o-ring materials with helium at room temperature, and with some HFC refrigerants at various temperatures. What test method can be used to generate the permeability data?

: The purpose is to determine how much leakage is expected to occur when testing the ass'y with Helium, and how much leakage to expect in the field with refrigerant.