Best coating/finish on Aluminum valves for LOX/Nitrogen/Helium service at Cryogenic Temperatures

[bogiedreamer]

We are having many issues with valves that perform well at ambient but then leak at Cryogenic temperatures. We have done things like:

1. Use heavy spring PTFE jacket seals
2. Achieve surface finish of 4 Ra uin on both the gland ID and gland OD
3. Use Krytox grease

I think the problem is at Cryo, the PTFE jacket is too stiff and the spring doesn't provide enough load to fill up the crevices and imperfections of the gland ID and OD even at 4 Ra uin. Currently surface are anodized aluminum. What coating/finish do you recommend to solve our problem?

 

[NGiLuzzu]

Bogiedreamer,
what kind of valves are we talking about?
The leakage is through the stem sealing only, isn’t it? How about the leakage through the closed valve?
Does aluminum withstand cryogenic temperatures?

Regards,
’NGL