When Should Oil be Filtered?

Noria Corporation
Tags: contamination control

"Our lube technicians recommended that we start filtering our new oils right out of the sealed drum with a 3-micron filter. Do you think this is necessary?"

Just because a drum is sealed doesn't mean the oil it contains is free of abrasives. There is a common misconception that new oil equals clean oil. There is no guarantee of this. The base oil, blending, packaging and logistic processes can all lead to contaminant ingress. Likewise, drums are never perfectly clean, particularly if they are reconditioned steel drums. New plastic containers are generally the cleanest, followed by new steel drums.

A good rule of thumb is that it costs 10 times as much to remove a gram of abrasive particle once it has entered your system than it does to exclude it in the first place. It can cost 10 to 1,000 times that figure, or more, to leave the gram of abrasive contaminants in the system, depending on mechanical design, machine criticality, contaminant abrasiveness, etc.

For those wondering what is meant by excluding a gram of dirt, it’s a rather simple concept. First, figure out what the contaminant is (dirt, coal dust, fly ash, etc.) and then determine the point(s) of entry (tank vent, worn seals, hatch, etc.). Some do this by examining particles found in used filters and sump sediment aided by common laboratory tools (XRF, SEM, optical microscopy, etc.).

For many machines, the inhaling of airborne contaminants into reservoir and tank headspace is the primary source of contamination. Forced convection of air by thermal syphoning, machine-driven air currents (e.g., movement of gears, plunging oil return-line flow) and cyclical changes in the tank oil level (hydraulic cylinder movement) can escalate the ingress. Air typically enters through vents and breathers, past shaft seals, unsealed hatches and cleanout covers, and other unprotected machine openings.

New oil is also a source of contamination, as are invasive inspection and repair activities. Hydraulic systems using linear actuators receive a high percentage of their particles from ingression past worn wiper seals and rod seals. Of course, mechanical wear, corrosion, oil degradation and surface exfoliation are also common sources of solid particles.

Filtering new oil is among your cheapest options for improving the mechanical reliability of bearings, gearing, hydraulic, systems, engines, etc.

In my opinion, your lube techs are on the right track. If they were mine, I'd support them on this initiative.

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