HP 5973 Hardware Manual page 200

Vacuum System
5
Diffusion pump and fan
You can check the condition and level of the diffusion pump fluid through the win-
dow (sight glass) near the base of the front of the pump. If the level drops below
the appropriate MIN marker (there are separate lines for hot and cold conditions)
or if the fluid turns dark brown or black, replace the fluid.
Diffusion pump fluid that is exposed to air at operating temperature will break
down and turn dark brown or black. This reaction is called cracking. Cracked
pump fluid gives two symptoms: higher manifold pressure and high background
with a large peak at m/z 446.
See Also Maintaining the MSD, page 93
Troubleshooting (HP 5973 MSD) in the online help for information on trouble-
shooting air leaks and other vacuum problems
200