The oil used in the vacuum pump can become contaminated. It should be changed after every 10 hours o f operation or immediately after evacuating a wet or contaminated system.
Moist vapor passing through a vacuum pump condenses into a liquid and mixes with the vacuum pump oil unless the pump is equipped with a gas ballast. All quality vacuum pumps have a gas ballast that should be opened during the early stages o f a pumpdown. This valve introduces air into the second stage of the pump. This air mixes with the vapor being evacuated from the system and minimizes pump oil contamination. The ballast valve can be opened or closed at any time when the pump is running, but should be closed each time the pump is started. Oil may be discharged during the first revolution if it is left open.