I have 2 YJ 6 CFM vacuum pumps.
The older unit is 15 years old and has in the past pulled down to 17 microns using my YJ 69075 vacuum gauge.
A few weeks ago I was pulling a vacuum on a system which had a burnt out compressor and I ended up getting a lot of contamination in the pump.
I needed 3 oil changes to get the system down to 400 microns.
I then tested my vacuum pump and was only able to pull it down to 107 microns. 1 week and 4 oil changes later and I'm now able to pull 24 microns.
My newer YJ 6 CFM pump which is about 2 years old has never been able to pull lower than 31 microns.
Does anyone else test their vacuum pumps to see how deep they can pull?