Vacuum Pump Technical Tips
Posted on May 11 2020
At the Chemtech Scientific Repair Lab, we are often asked: “How often should I change my vacuum pump’s oil?” Every month? Two months, six months?
The answer is that there is no set interval for changing a vacuum pump’s oil, as the oil change requirements are process driven. It is a mistake to treat your vacuum pump’s oil supply like that of an automobile. An automobile’s oil system is a sealed system and the engine manufacturer can predict the life expectancy of the oil based on miles and/or months the oil has been in use.
A Scientific Vacuum Pump’s oil supply is not sealed off in a closed system, as that of an automobile. An oil sealed Scientific Vacuum Pump is used to lower the pressure of an application appliance to below 1 Torr (1/760 of atmosphere) and lower. At the operating pressure, most liquid compounds will vaporize and be expanded into the vacuum pump. The vacuum pump will compress and therefore condense the condensable vapor to liquid into the pump’s oil reservoir as a contaminant to the oil.
The contaminant will react with the vacuum pump’s oil (even water). Contaminants will act as an initiator and the agitation (rotation) and heat of the operating vacuum pump increase the rate of reaction. Water and other immiscible compounds may make an emulsion with pump oil and greatly degrade the lubricating properties and vacuum seal properties of the pump oil, fueling heat and a more rapid reaction, degrading the oil further.
The best answer to oil changing requirements is to inspect the pump oil frequently and change when the oil color is nearing “D” on the following color chart, or showing signs of emulsion “H” on the chart. It is best to use Chemtech Grade 33 Vacuum Pump Oil (CTS 33 "A" on chart). A clear oil, free of impurities. Many vacuum oils are already at color “A” and are straw color when new. 
It’s best to use Chemtech Grade 33 Vacuum Pump Oil (CTS 33 on chart). A clear oil, free of impurities. Many vacuum oils are already at color “A” and are straw color when new. The impurities in straw colored oil will easily react with process emissions in the vacuum process and require more frequent oil changes.
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