Benefits and Dangers of Filtering Oil
June 22, 2018
Filtration across all applications. Why not just filter the heck out of your oil? What's good practice in this area?
We get asked this question quite a bit because there's an awful lot amount of documentation and articles written about filtration and the effect of lengthening the life of bearings and components based on how clean you get your oil. It's all certainly true, the cleaner oil is always better oil. But there is cost of filtration and a lot of times the need for very, very fine filtration is going to be dependent on the application itself. A hydraulic oil application, for instance, has some very high tolerances and can typically benefit from very fine filtration where gear oils the tolerance may not be so tight. You're dealing with more viscous oils and you kind of have to counter the cost of the filtration versus the real benefit you're getting from the filtration.
In these applications that need really tight filtration is there ever a risk of filtering out the additives that have been put in there?
That's a good question because it's really kind of debated on whether you can or not. A few of the additives, especially the anti-foam additives can be very large molecules and there are some school of thought that you can actually filter out those larger molecules with very fine filtration and lose the effectiveness of the anti-foam in the formulation. That's probably not the case, but what you can get is the additives are not totally solubilized in the oil and there can be what's called an agglomeration, where the additive kind of joins together with other like molecules to form bigger molecules. So over time you might have a situation where you have a big enough molecule there that can be removed by very fine filtration and you see the effect of it as a foam problem in the application over time. But typically you don't worry about that and you're not going to typically filter out an anti-wear additive or anything like that because the molecules are just too small and they're all very well solubilized in the oil.
So what are some common errors? Are there common filtration errors or common misconceptions that people come in with?
Well I think when you're talking about filtration, I think generally there is a misunderstanding of what filtration you can accomplish based on the filter that you're buying. When you look at a Micron rating on a filter, say you've got a 5 micron filter, well that's only one piece of the puzzle. You can have a 5 micron filter that's only 50% efficient so it's got a beta of 2, for instance. A 5 micron filter with a beta of 2 is 50%, meaning on a pass-through it's only going to take out 50% of the solids that size. So you're not getting a very good idea of how good a filtration you're actually getting, whereas the same 5 micron filter with a hundred beta then it's 99% efficient. So it makes a big difference in knowing what you're actually buying in filtration.