DIFFUSION PUMP MAINTENANCE GUIDE
Depending on the type of diffusion pump oil you use, maintenance can be relatively simple to very time consuming. As discussed in our article covering the difference between hydrocarbon based and silicone based diffusion pump oil, we generally recommend our customers use silicone based diffusion pump oil. Using silicone based oil, there is little or no maintenance required, just several things to do on a routine basis. On the other hand, using hydrocarbon based diffusion pump oil can result in more frequent required actions that are quite time consuming. Depending on your application and if there is possible contamination from your vacuum environment into the diffusion pump chamber, diffusion pumps using hydrocarbon based pump oils should change the oil every 3-6 months. If you’re using silicone based diffusion pump oil, an oil change is not required for at least 12-18 months. Of course, if your application contaminates the pump oil, more frequent oil changes maybe required. In the case that your application requires very frequent oil changes, you can consider using hydrocarbon based pump fluid as it is cheaper.
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WHEN TO CHANGE THE DIFFUSION PUMP OIL
One of the major differences between hydrocarbon and silicone based diffusion pump oil is its oxidation rate. As hydrocarbon based oil oxidizes relatively quickly, it turns very dark and thickens with use. After 3-6 months of repeated heating within the pump chamber, charred deposits will slowly clog the pressure jets decreasing the vacuum rate and pressure. When you notice this decreased vacuum effectiveness, you’ll know that an oil change is required. Additionally, you can routinely check the color of the oil. New hydrocarbon based diffusion pump oil is transparent and usually has a slightly yellow tint. When the oil turns dark and opaque, it is time for an oil change. Silicone based diffusion pump oil can be used for a much longer period of time if no outside contamination occurs and when there is minimal air leakage within the diffusion pump. Silicone oil used in high vacuum environments offer optimal performance due to its low vapor point and high resistance to chemicals, oxidation, and even radiation. Based on experience, the average oil replacement times range from 12-18 months. New silicone based diffusion pump oil is clear and colorless. With use, it attains a slight yellow tint. For the most part, the discoloration of silicone based oils do not necessarily affect performance.
STEPS TO REPLACE THE DIFFUSION PUMP OIL
As mentioned earlier, replacing hydrocarbon based diffusion pump oil can be time consuming as there will be quite a bit of residue that is not easy to remove. Please use the following steps.
- Turn off the diffusion pump and let cool. Ideally, you want change the oil when diffusion pump is still warm.
- Depending on your assembly, drain the diffusion pump. There is usually a drainage port.
- Drain the oil into a container and set aside for disposal by a professional company.
- For diffusion pumps using hydrocarbon based oils, you should dismantle the pump and clean it with a solvent as there will be residue that clog the pressure jets within the diffusion pump. Afterwards, rinse with alcohol and de-ionized water to remove the solvent. You should dry with dissembled pieces with compressed air or let air dry. Reassemble the diffusion pump and pour in the new diffusion pump oil. Make sure you add high vacuum silicone grease to joints and o-rings.
- For diffusion pumps using silicone based oils, dismantling is usually not required. Just completely drain the used oil through the discharge port and replace with new pump oil. Generally speaking, diffusion pumps were not meant to be frequently dismantled. The more often you dismantle it, the easier it is for the seals deteriorate causing air leakage.
- At this time, make routine checks on the fore pump, temperature gauges, double check the seals, and run a leak test on the entire system.
Diffusion Pumps are by far the most efficient method of high vacuum pumps. To maximize its potential, proper maintenance is key.