Considerations When Using Grease in a Vacuum System

There are many considerations when utilizing grease within a vacuum system. Often grease is used for the lubrication of o-rings, mechanical components, and in some cases to prevent corrosion. However, it is highly recommended to consider whether a grease is even necessary for each application. The presence of grease within a vacuum system can increase the gas load on the system and can be a source of collecting foreign debris. Moreover, greasing components within a vacuum system requires a conservative approach and diligence to ensure that proper cleaning of the greased components happens at regular intervals.

In most cases, a little grease goes a long way. O-rings used in static sealing applications only require enough grease to give the appearance of a shiny sheen. Copious amount of grease are not required and are actually discouraged. Excessive amounts of grease can be a trap for dust and debris which can affect the overall performance of the vacuum system. Trapped debris within the grease may lead to leaks around a greased o-ring. It is recommended that periodically, any components or o-rings and their mating counterparts should be cleaned, degreased, and new grease reapplied. The period of cleaning and reapplication is best determined by operational data which may include how often the component(s) are accessed. If it is frequent, one may elect to clean every nth cycle. If the component is only accessed rarely, it may be prudent to clean and regrease each time the component is accessed and available for brief maintenance.

There are a wide variety of greases available. However, only a low vapor pressure grease should be used for a vacuum system. There are two primary reasons for using a grease with characteristically low vapor pressure: Primarily, low vapor pressure greases resist migration within a vacuum system. This means that despite very low pressures, the grease will remain intact and not vaporize, thereby coating all of the components within the system. For many applications, grease migration would contaminate the process or equipment within the system. Additionally, a grease that migrates is not remaining in its original location. Therefore, the very components it was supposed to protect may be vulnerable. Secondarily, low vapor pressure greases will contribute much less to the total gas load of the system than a non-vacuum rated grease. The increased pressure from a high vapor pressure grease may prevent a system from reaching its operational pressure.

Two primary forms of grease are rated for vacuum service; those are silicone-based and hydrocarbon-based greases. Each serve different applications. Namely, silicone-based vacuum grease has a higher vapor pressure than most of its hydrocarbon counterparts but is substantially less expensive. Silicon-based greases also tend to be much more difficult to clean. This is especially important if a vacuum technologist is performing periodic maintenance to the greased components or o-rings. Hydrocarbon-based greases fill many applications. Moreover, hydrocarbon-based greases can operate at much lower pressures (UHV) and in a wide array of temperatures.

High Vac Depot proudly sells Dow Corning silicone-based greases and Apiezon hydrocarbon-based greases. Apiezon offers a wide array of hydrocarbon-based greases that offer differing levels of lubricity and vapor pressure at different temperatures. Check out out our well-stocked selection of vacuum greases at here.