The tight tolerances found in today's hydraulic systems require hydraulic fluids to be as close to "contaminant-free" as possible.
"Clean fluid is essential to the life of hydraulic systems," says Diego Navarro, service marketing manager, John Deere Construction and Forestry. "The higher the operating pressure, the cleaner the fluid needs to be."
Rudy Urbano, hydraulic consultant, Caterpillar, points out, "On a high-pressure piston pump, the only thing that separates one moving part from another is a film of oil. That film of oil is about 1 to 2 microns thick."
Caterpillar specifies an International Standards Organization (ISO) code range of 18/15 for its equipment hydraulic systems. "When you talk about an 18/15 ISO code, you're talking about [the number of allowable] particles that are 5 to 15 microns in size," Urbano notes. "So even in an 'acceptably dirty' system at 18/15, your particles are still going to be bigger than the film of oil separating the machine components. In addition to hard particles, you also have the chemical contamination of air, heat and water."
As the size and volume of contaminants increase, equipment performance suffers, and you face the risk of premature failure of pumps and other components. Fortunately, there are precautions you can take when storing and handling fluids that can help to mitigate this risk.
Monitor bulk fluids
If you have a sizable fleet requiring larger fluid volumes, chances are you're using some form of bulk storage tank. If so, it's important to periodically check the condition of the fluid, the tank and the delivery system to the machine.
"A lot of the bulk storage tanks don't really get checked for contamination. The assumption is it's a big tank, so how much contamination can be in there?" Urbano asserts.
Yet, he cites an example of a tank that had been in use over a 20-year period. The owner assumed the oil was clean since it was purchased in bulk from the refinery. But when the tank was drained, they discovered 18 inches of contamination had settled out to the top of the spigot.
The contamination was likely introduced during transport from the refinery to the tank. "After refining, the fluids travel long distances through piping networks at the processing plant, then to containers or bulk transportation tanks and, finally, to the users' tank," says Navarro. "Every time the fluid changes from one container to another, it is basically cleaning the container in which it travels, carrying the contamination to the next one."
Over time, any solids picked up during transport will settle and accumulate at the bottom of the tank. "Just checking your bulk tank to make sure it's relatively clean is a big step," says Urbano.
In addition, the majority of bulk tanks have a breather open to atmosphere that allows air in as oil is drawn out. Urbano recommends a minimum of a 4-micron air filter to ensure airborne contaminants will not be drawn into the tank.
Water can also do significant damage to hydraulics. "Most hydraulic systems are designed to shed water," notes John Sutherland, national accounts manager, Chevron Products Co. "So you have a layer of hydraulic oil and underneath that you could have a layer of water. Depending on where the pump suction is on the hydraulic system, you could suck that water into the system right at the beginning." This can produce sluggish performance of hydraulic functions, plus lead to rust, which in turn generates wear metals in the fluid.
Condensation is generally the culprit behind water contamination in stored fluid. A desiccant breather/filter can reduce the degree of both dirt and water ingress into the tank.
Bulk fluid condition should also be periodically analyzed. "Checking bulk fluid cleanliness periodically through lab oil analysis or on-site equipment is the best possible practice," says Navarro. "It helps the user to gauge delivery consistency and identify risky contamination. It also allows the user to test if the product he gets actually matches the signature of the product he expected."