Changing oil more frequently will enhance the life time of a vacuum pump. If the vacuum pump is pumping condensable vapours for example, freeze drying, it may be necessary to change the oil after each process so as the pump does not stand idle with contaminated oil.
▶ Do not mix synthetic oils with mineral oils
▶ Oil contamination is usually indicated by a poor vacuum or oil with grey or milky appearance. Should liquids be accidentally allowed into the pump, change oil immediately