The most common cause of a loss in efficiency in a mechanical pump is contamination of oil. It is caused by condensation of vapors and by foreign particles. The undesirable condensate emulsifies with the oil which is re-circulated and subject to re-evaporation during the normal cycle of pump activity, thus reducing the ultimate vacuum attainable. Some foreign particles and vapors may form a sludge with the oil, impair sealing and lubrication and cause eventual seizure.

Periodic oil changes are necessary to maintain efficient operation of the system. The required frequency of changes will vary with the particular system. Experiences with the process will help you determine the normal period of operation before an oil change is required.