If you own or work with a vacuum pump, it is highly advisable that you get to familiarize yourself with the oil that it uses. There are different types of vacuum pumps and each has its own set of requirements for the oil it uses. This oil needs to be constantly inspected and changed.
Such vacuum oils come in silicone, hydrocarbon, and other types that are specifically designed for vacuum applications only.
The purpose of vacuum pump oil is to act as a mechanical lubricant and as a medium that traps gas molecules. This oil is chemically stable with low-vapor pressure and doesn’t react to gases and materials.
How Vacuum Applications Work With Oil
Substances tend to boil and shed molecules in a vacuum. In the passing of time, vapor pressure tends to build up which contaminates the vacuum. Substances such as water boil greatly into a vacuum while others like glass boil minimally.
As such, a vacuum application needs to have, among other things, clean oil, in order to maintain a vapor pressure measuring 10^-5 Torr or less.
A diffusion pump has a heated oil spray where gas molecules are collected. This pump uses hydrocarbon, perfluorinated polyether (PFPE) or silicone oil depending on the vacuum application.
Mechanical vacuum pumps have rotary parts and valves that are designed to pump from atmospheric pressure. They make use of hydrocarbon oil to lubricate their parts and to seal the vacuum.
Another role of oil in a vacuum pump is cooling the pump during heat transfer. As this oil gets saturated by non-condensable substances and moisture, the efficiency of the pump is greatly reduced. Maintaining clean oil in the vacuum pump guarantees its maximum operation and an increased lifespan of the pump.
How Often Should You Make A Vacuum Pump Oil Change?
Vacuum pump manufacturers have different recommendations of when you should change the oil in a vacuum pump. Some manuals recommend an oil change be done after every 300 running hours. This amounts to a period of around 2 weeks if the pump runs on a 24-hour basis non-stop.
In such a case, the extended use of the pump before changing the oil may send vapors or dust to the pump and end up contaminating the oil. If the oil gets contaminated by condensed vapor, the generated vacuum will deteriorate owing to the water that has been mixed with the oil.
This water has a vapor pressure measuring around 18Torr which means that the liquid will evaporate all over again on the inlet side of the pump cycle resulting in the pumping volume being filled with vapor. The pump will then be left with little to no volume to pump gas from the process. This will, in turn, trigger the process chamber pressure to rise.
If the contaminant from the process chamber is powder or dust, it will end up mixing with the vacuum pump oil, resulting in mechanical wear of the bearings and the close-fitting metal surfaces with an oil film between them.
If you own a rotary piston pump, you may have noticed the effects of solid contamination on the pump’s lower hinge bar. Worse still is the wear and tear that takes place on the pump bearings that’s hard to notice owing to the circulation of oil through the bearings.
The recommended method of changing oil, then, is that you analyze the process of use of the pump and then establish your own guidelines of oil change.
The Do’s And Don’ts When Handling Oil In Vacuum Applications
1. Ensure That There’s An Oil Change After Every Evacuation
This is by far one of the most important things you can do to care for your vacuum application and to get to the deep states of vacuum. It’s paramount that you perform every evacuation with uncontaminated oil that is moisture-free.
2. Use The Correct Vacuum Pump Oil
Doing so not only preserves your equipment’s warranty, but also saves it from damage.
3. Flush Out The Oil After Five Changes
If you’ve noticed that the oil in your vacuum pump is contaminated or has been in the pump for more than one month, it’s advisable that you flash it out whether it is contaminated or not.
4. Avoid Pulling A Vacuum With Contaminated Oil In It
Oil, in some cases, does get extremely contaminated when an evacuation is taking place. In such instances, it’s advisable to replace the oil during the process.
5. Never Start A Pump Before Adding Oil
Oil is essentially the lifeblood of the pump. Ensure that you fill it with clean oil before starting it.
Now that you’re well informed on the importance of clean oil in vacuum applications, here are some helpful insights on how to prevent oil contamination.