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A diffusion pump is a relatively simple mechanism for producing a high vacuum. There are no moving parts and the entire system really consists of a handful of parts. However, due to its simplicity, optimizing each aspect of the pump will contribute to improving the overall efficiency of your operation.

In this article, we’ll take a look at the benefits of covering the o-rings and joints of your diffusion pump with high vacuum silicone grease. As diffusion pumps create and maintain high vacuums, it needs to operate in an airtight environment. There is no concern of leaks occurring on the body of the diffusion pump as it made from a single stainless steel piece. Instead, your attention should be focused on the joints and locations of the o-rings, these are the weakest parts of a diffusion pump where air leaks can occur. These locations should be routinely monitored for leakage making sure they are properly sealed with grease.

Much like the type of diffusion pump oil to use, grease can also be generally divided into hydrocarbon based or silicone based grease. While there are many high temperature hydrocarbon greases to choose from, we suggest going with silicone based version. Silicone high vacuum grease generally milky white and is thicker in composition. It offers better resistance to corrosion, is water and moisture proof, and is generally considered a better type of grease for lubricating rubber parts such as o-rings as hydrocarbon based grease tends to swell and soften rubber under heat.

Additionally, due to the thicker nature and high temperature endurance of silicone grease, it does not melt or become runny causing potential contamination to the vacuum system. All in all, silicone high vacuum grease should be considered over hydrocarbon based grease. The use of better grease will lead to lower maintenance costs and higher vacuum pump efficiency in the long run. This is true especially for relatively high vacuum applications that require vacuum pressures above 10-8 Torr where heating temperatures are much higher and overall stress on the diffusion pump is increased.


If air gets through, the oil turns into a consistency much like gel.