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“What are the most common ways contaminants can enter fluid systems?”
Contamination control can be divided into two main parts: exclusion and removal. Since neither method is sufficient on its own, both must be considered for a good contamination control strategy.
For contaminant exclusion, it is critical to understand the possible sources of contaminants and their ingression points in the system. External contaminants may be introduced through any ingression point, such as a breather, seal, port, hatch or other inlet.
Although most people think of contaminants as only coming from an external source, they can also be generated internally. In addition, don’t discount the likelihood of human interaction with the system as the source of contamination. These three types – externally ingested contaminants, internally generated contaminants and contaminants created by human interaction — are the primary sources of contamination in a system. Following are a few examples of each:
Contaminants can enter a system due to poor seal design, worn seal materials, and operational or environmental conditions. Failed shaft seal points may ingress external contaminants or internal process materials. For hydraulic components, wiper and rod seals inevitably will leak both externally and internally as contaminants damage the seal materials during extended operation.
Any breathable headspace point also provides an opportunity for road dust, soil, rock dust, moisture or other contaminants to enter the system. Even when a machine is equipped with an appropriate breather, if there are gaps in the hatches, ports, etc., air is more likely to be “breathed” in within these areas of least resistance.
If left to oxidize or thermally degrade and used over an extended time period, a lubricant’s constituents can turn into abrasive contaminants. This can result in oxidation insolubles, sludge, additive fallout, etc. Rust is a symptomatic contaminant from the ingression of water. It can cause iron to corrode and form red-iron oxides. Soot is a fine carbon insoluble that frequently is generated from the thermal breakdown of hydrocarbons. Fibers from seals, hoses, filters or other materials can also leave contaminants to invade the system. Additionally, friction can lead to particles forming as a result of adhesive, abrasive or fatigue wear.
When oil or grease is added to a system, the new lubricant often is not clean and can bring a variety of potential contaminants. Likewise, as machines require internal work, such as to replace bearings and seals, the fluid reservoir may be exposed. Machining swarf, welding spatter and sealants or adhesive materials are all examples of debris that can be left behind from human interactions with the equipment.
Fitch, E.C. (1988). Fluid Contamination Control.