Oil isn't just used to lubricate moving parts inside a pump, but it is also utilized in sealing any fine clearances inside a pump. This extra function means that the oil needs to circulate at a rather high rate in order to make sure that a sort of 'wedge' of oil forms up before crucial moving surfaces. One such instance would be the vanes, specifically their rubbing edges.
Dealing with Oil Mist
This high-velocity movement of the oil is great for preventing air leaks throughout the interior of the pump. However, turbulent oil flow may result in an oil mist, especially on the pump's exhaust side. The exhaust cavity of your pump needs an exhaust filter or oil mist evaporator in order to prevent this oil mist from being discharged to the surrounding environment. Alternatively, exhaust can be routed out of the building.
A pump's oil mist separator is composed of a fibrous material. Different types of material are available for different processes such as highly corrosive, or reactive processes. This material gets 'wet' when oil molecules come into contact with it, and the element triggers the oil molecules to start coalescing into bigger droplets. Most of these oil molecules, although not all of them, go back to being a liquid oil when they go through the material before they're discharged externally as droplets, or depending on the style of exhaust filter, oil can coalesce and drain back into the vacuum pump.
Over time and with repeated use, your oil mist separator is going to accumulate contaminants. These contaminants restrict airflow through the separator, resulting in higher back pressure going up against the pump. This higher pressure means the pump and motor both have to work harder, which results in overheating and possible damage to the case gasket and/or shaft seal. It is recommended to check the filters on your oil mist eliminator from time to time to see if the filters are saturated and need to be replaced.
Serious contamination can cause the separator to rupture, which can lead to a rapid oil discharge out of the pump, and possibly even pump seizure. In this case, you should replace your oil mist separator element before things can get this bad.
As already mentioned, not every oil molecule coalesces when it's inside the material element of the oil mist separator. Every once in a while, certain molecules will go through without actually coalescing with any of the other oil molecules. The final result from this is that a tiny portion of the oil molecules is directly discharged out of the pump exhaust.
Typically speaking, that number is going to be so low that it's not a matter of any real concern. However, you might detect a mildly oily smell from your pump. Also, some oil might condense on any exterior surfaces of your pump that are colder than others, particularly on the inside of the exhaust elbow, when one is fitted. Given all this, an occasional oil drip underneath your pump exhaust isn't really something to stress over, particularly when your pump needs to move lots of air. If you get more than a drip each hour, though, then you might have issues that need to be dealt with.
Dealing with Excessive Oil Discharge
There are a number of reasons why you might be seeing excessive oil discharge from your exhaust.
- The first one is simply that the oil level is too high. This needs to be the very first thing that you check. When the pump is not running, be sure that your oil level you see in the sight glass is underneath the MAX mark. If you don't see an obvious maximum allowable oil level, then just keep your oil level at around 75 percent of what's on the sight glass.
- Another possibility is that the exhaust oil mist separator's element got overloaded with contaminants or damaged, so it no longer functions. The life service cycle of any element is going to vary based on how much contamination there is, but in typically clean conditions along with routine oil changes, you should expect approximately 2,000 operating hours.
- Your exhaust oil mist separator might not be properly seated in its designated housing within the exhaust cavity. To look for this, check out the seal that's on the end of the element. Attempt to re-tighten your element. If it's a screw-in element, don't use too much force. That might rupture your element.
- Your pump likely has an allowable range for continuous operation. Running it for a long time outside of this can lead to issues.
- The oil return in your exhaust cavity could be blocked.
As you can see, there are many different potential causes for your vacuum pump to be spitting out oil or just discharging it. In some cases, it's nothing to worry about. In others, you can prevent issues by keeping the oil level right, changing it as directed, cleaning the machine, and operating it within normal parameters.