Hydraulic systems get their contamination from four primary sources—new oil, built-in, ingressed and induced. Contrary to popular belief, new hydraulic fluid is not clean. The manufacturing and handling process exposes the fluid to various forms of contamination, and although I wouldn’t call it filthy, it’s often times many ISO codes higher than ideal fluid.
Built-in contamination is a by-product of the manufacturing and assembly of your hydraulic machine. It could be welding slag from reservoir construction, metal filings from tube cutting, particles from cylinder honing or water condensation from old pump sitting on the shelf. Anything existing from the creation of the hydraulic circuit not needed there for operation is a form of contamination.
Ingressed contamination comes most often from poor maintenance practices of your hydraulic system. When your technician removes the filter cap to add oil, how does she ensure junk doesn’t drop right into the hole? Also, how clean is the funnel used to help pour in the oil? Secondary ingression can come from water sources, such as the coolant contamination of the hydraulic functions on machining centers.
Remember, water is a source of contamination, not just particles.
Induced contamination comes from the wear of the internal components of the hydraulic system. Bronze from pump valve plates, steel from cylinder barrels, cast iron from valve bodies or even polymer contamination from seal wear, are all areas to be concerned with, as each can generate harmful particles.
All those are sources of hydraulic contamination, but are only contributors to hydraulic system dirtiness.
But the real reason your hydraulic system got so dirty, is because you don’t clean it. Nobody really wants to know why or how your underwear got dirty, but we only want to know you clean them often. Hydraulic systems get so dirty because they’re not being cleaned as quickly as the dirt is being generated.
Ensure you use high quality filtration that removes all but the most microscopic particles of your system. Any level of contamination can act as a lapping compound, which itself creates more contamination, perpetuating a vicious cycle. Not only is it important to use the highest quality filtration possible, you must monitor its effectiveness through bypass indicators and an oil sample program.
Introduction of contamination is a fact of any hydraulic system, but the reason your system is so dirty is because you’re not cleaning it well enough.