Diffusion pump oil change frequency

[BCBC]

How frequent would one change diffusion pump oil? I've talked to people who never change it if the color is clear. Maybe some top it off a bit if low.
This is for Agilent systems. Varian I believe is the manufacturer.
Thanks very much.

[Ron]

The recommendation used to be change the oil annually. I have never known anyone to do that, but every couple of years is a good idea. I have seen too many diffusion pumps filled with black sludge, and they are a pain to clean.

[AICMM]

BCBC,

The bigger issue should be how often you change your rough pump oil. That should be done annually at a minimum. This is probably where most of the gunk ends up anyway.

Back in the days, I would easily go 2-3 years without changing the diff stack oil.

Best regards.

[Kostas Petritis]

We did see that the frequency depends highly on the oil that we were using. I do not remember exactly the types anymore, but with some types the oil was getting "black" pretty quickly.

We are currently moving towards scroll pumps which are oil free, require maintenance once per year, are much less noisy but twice as expensive...