It depends on at least three factors.

1. Amount of use.
2. What type of environment you are pulling a vacuum on. What gases are
likely to be pumped by the oil diffusion pump. Some might react with the
oil.
3. I think some pump systems also have some type of filter on the oil to
remove corrosive or reactive components or solids.

I didn't know that oil diffusion pumps are still used. They are
notorious for inadvertent backstreaming into vacuum systems.

Ed Sebesta
Program Manager VLSIP Technologies

-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org] On Behalf Of Nataraj
Sent: Thursday, July 09, 2009 7:17 PM
To: mems-talk@memsnet.org
Subject: [mems-talk] Frequency for changing Oil in Oil Diffusion Pumps


Dear All,

              Can any one advise me, what is the frequency for changing
the Oil in Oil diffusion pumps?  Is it time based or does it depend on
the utilization of the machines.

Regards,

Nataraj Santhanam
Sputtering Section