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Sometimes you can ask 10 people the same question and get 12 different answers. That's no good if you’re gathering eyewitness accounts of a crime. But if you’re looking for the most effective ways to improve machine operation and reliability, the more information you have, the better.
We queried hydraulic filtration product suppliers about some of the best practices people can follow to hold fluid contamination at bay—especially when on a tight budget. Here's a summary of their responses:
Keep in mind that micron ratings of filter elements can be an important consideration in the operation of hydraulic systems outdoors in winter, or in extremely cold indoor environments. If a system cannot generate sufficient heat to cause the oil to flow freely through the filter, the oil will bypass the filter. Constant bypass means no filtration.
Place filters where they can be easily serviced and replaced. The more difficult it is to see or reach a filter, the less likely it will be serviced.
The most effective way to keep dirt and moisture out of a hydraulic reservoir is to completely seal the reservoir from the ambient environment. Replacing the air space above the fluid in the reservoir with dry nitrogen increases effectiveness by reducing oxidation of the fluid.
Don't judge a filter housing by its maximum operating pressure. When sizing a filter, look for the manufacturer’s Cyclic Fatigue Rating (NFPA T2.6.1). A cyclic fatigue pressure is lower than the operating pressure and verifies the fatigue pressure rating of the pressure-containing envelope of a metal fluid power component.
All hydraulic filters should be fitted with visual or electrical indicators or both. The visible signals allow easy and clear monitoring of the filter element status, and electrical indicators can be wired remotely to provide information at a central control panel or off-site location. Then, of course, don't ignore your indicators! If you do, and the filters go into bypass mode, you're just dumping dirty fluid back into the system. Filter bypass mode was designed to enable cold starts on mobile equipment until operating temp is reached.
Frequent oil analysis is important in preventing problems. Don't take oil samples from the bottom drain port of the reservoir because all the big chunks of dirt and gunk fall there. Do take oil samples from a turbulent point in the system—from a working line while the system is running—to get a representative sample.
The question should not be how clean can you get your oil, but how dirty can your oil be and still give you very good pump, valve, cylinder, and seal life. On the inlet side of a pump, always size the filter at least one size larger than the pump inlet port. Keep the inlet line velocity down to 4 ft/sec.
Locating a coarse filter upstream of a fine filter can improve the useful life of the fine filter by preventing larger particles from reaching the fine filter.
Remember that filters must be sized for maximum flow, not average flow. Use the largest capacity filter that you can fit into available space, with flow capability at least twice that of maximum times flow.
When sizing a filter, remember to consider startup conditions. During startup or cold operating conditions, fluid viscosity may be higher than during operating conditions, meaning that a larger sized filter may be required. In addition, when âP indicator is used, a thermal lock should be considered to prevent premature tripping until the fluid reaches normal operating temperature.
Finer filtration is not always better. If equipment requires 10 µm, 3-µm filtration does not necessarily provide a better option. The 3-µm element will clog faster, resulting in more frequent element changes, and higher service and product costs.
It's a common misconception that coarse filters last longer than fine filters. This is not really the case. Once a fine filter has removed particles from the system and stopped wear from occurring, there are few particles left to be removed—and thus, long life. On the other hand, a coarse filter doesn't prevent wear, so particles will continually need to be removed.
Desiccant breathers have become the new standard for keeping dirt and moisture out of hydraulic reservoirs. Use them to remove dirt and moisture that would otherwise be drawn into the reservoir during normal equipment cycling.
Record inspection and replacement intervals where they can be observed and compared. As frequency of replacement increases, it's a warning of component failure. When you do replace a filter element, inspect it for trapped metal. An increase in yellow metal shows a failure in wear plates or slippers. An increase in white and gray (ferrous) metals indicates wear caused from contamination or cavitation. Black, carbonaceous material; sticky, gooey varnish; or gray ash may indicate excessive heat and signal time for an oil change. Inspect the system to determine what is causing the heat.
Consider using a portable filter cart for large mobile systems exposed to dirty environments. Portable filter carts can be your best investment by keeping multiple machines clean without having to install a kidney loop on each machine.
New oil is never clean. Therefore, do not add fluid to a system without pouring it through a filling filter. This fine-mesh filter should be rated at least β10 75 (10 µm absolute).
If you're not sure when to change a filter, install a pressure differential indicator on the filter adapter. All the guesswork is gone!
Inspect used filters as a predictive maintenance tool. If metal debris is noticed on the surface of the filter media, good magnification and wear metal analysis can pinpoint the source of the metal. This way, components that will obviously break down soon can be changed out during a scheduled down period. Many thousands of dollars can be saved by practicing predictive—rather than reactive—maintenance.
The level of filtration is only as good as the weakest filtration component—a 3 µm absolute return line filter doesn't mean 3 µm oil if the reservoir breather is 50 µm.
Typical oil additives, such as anti-oxidant agents, will compensate and balance chemical changes from oxidation. If oil oxidation has not been minimized, oil additives and base oil will transform into oxidation byproducts—waxy residues on valve surfaces and sludge on the bottom of the reservoir.
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This file type includes high resolution graphics and schematics when applicable.
