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Coming from the farm, oil mist was something that I became fairly familiar with, not because I had to deal with anything directly in any substantial way, but because I have always been a bit persnickety when it comes to maintaining my combine. My cab was always kept as spotless as I could get it. Anytime I had to stop my machine, I was out there cleaning my windows for better visibility; any place there was dirt building up on the normal flat surfaces, I would run over there and clean it up. One of the issues I started to notice was the build-up of dirt right on top of the feederhouse (a section of the machine that draws the cereal crop into the separator section from the header section) that seemed to always form in a strange but consistent pattern. Being a young guy and not having too many harvest seasons under my belt, I had no idea what was causing this, but I cleaned it up nonetheless.
With hindsight being what it is, I know that a fine hydraulic leak was the root of this build-up. A small pinhole in my hydraulic lines (I ran an older machine with an even older header) was causing a fine mist spray in a specific pattern onto that feederhouse, and all of the dust and chaff was sticking to that oil that would settle on the machine. There probably aren’t too many of you out there running a combine in a manufacturing plant, but believe it or not, this is relevant information We often forget about what is causing some of our minor (or major) headaches.
Oil mist/fog can be a good thing. If I have a high-speed turbine, I am likely to have a mist system incorporated into the lubrication of that turbine. If I have some obscure gearboxes that I keep on hand because they are hard to find, an oil fog being maintained inside the headspace can protect those surfaces.
The mist and fog we need to worry about is the stuff we aren’t generating on purpose. Oil is really good about sticking to stuff for the most part, so if I have a reservoir that has an open breather and it keeps generating a bit of mist, I will likely see indicators of this (as long as I know what I am looking at), like dust settling and sticking to the oil on top of the reservoir.
The mist is causing a bit of housekeeping, so what? What happens if I am maintaining the headspace in that reservoir? The oil is going to permeate the filter media and either plug a spin-on filter or coat the desiccant and prevent it from doing its job. So that little bit of mist could end up causing moisture accumulation in the headspace and oil, or it could create a situation where the reservoir won’t breathe at all.
If the reservoir needs to breathe and can’t, something else somewhere in that system is going to give. It might be a seal somewhere, control valves, or it could be that the machine goes into a safe mode and just shuts itself down. None of these situations are going to help production or reliability. So, the next time you walk past a reservoir, gearbox, hydraulic system or pump and you see that bit of dust that always settles in the same spots, or worse yet, actual mist coming out of the breather, take a minute to figure out why this is happening and what can you do to fix it.