Seal to seal-off gases

[Vic123]

We use O-rings for metal-to-metal seal, to seal-off liquids for a high temperature application. But elastomer are permeable to gases. What would someone use to seal-off both liquids and gases(no permeations allowed) for the same high temperature(400 degree F) application?

 

[israelkk]

If you are sealing face to face you can use soft machined metal O-ring seals. They can be made of Lead, Silver, Copper, Gold, Aluminum etc. They are for one time use, they are crushed between the sealing faces.

There are also elastic metal o-ring seals which has a closed hollow section or open C type section but I am not sure how good they can seal.

 

[Vic123]

But what if its not a face-to-seal? Its a male gland o-ring type application.

 

[israelkk]

Then I think you may have a problem and you may need to change the seal design to some kind of a face type. All rubber and plastic seals will permeate. If no permeation is needed then you have to my best knowledge to metal ro metal seal which needs very high contact stresses on the seal to be able to seal gases. The stresses are usually beyond the elastic limit of the seal material.

For example when we needed to seal a helium pressure vessel we used a coned 1100 alluminum disk that is crushed between the vessel openning and a cap.

 

[Vic123]

Thanks

 

[scalleke]

As long ar your gland is static you can use helicoflex metal o-rings.

Garlock-Helicoflex

scalleke

 

[israelkk]

scalleke

If you look at the Helicoflex on page 7 you will see that the seal is designed such that it may have an air leak at a rate up to 0.0001 cc/sec-atm. Meaning, at higher pressure difference the leak will be higher.

In the original post Vic123 says that even permeation rate is not allowed which is usually much smaller than leak rates so leak is absolutely forbidden. Therefore, I do not believe that Helicoflex will do the job.

 

[bogiedreamer]

This type of application is perfect for a spring energized teflon seal.

Teflon has low permeability, low friction (if dynamic), and with the spring energizing the seal is an extremely effective device in sealing hard to seal gases like N2, He.


check this out

http://www.seals.saint-gobain.com/Media/Documents/S0000000000000001018/OmniSeal_SelectionGuide.pdf