Hydraulic Filtration


by Darrell Harrelson

Most hydraulic machinery comes equipped with at minimum a particulate return filter. Sometimes these filters are supplied with an indicator gage to indicate that it is time to change the element. Good maintenance practice is to monitor these indicators for filter change intervals or some shops base filter changes on time. But is this enough to ensure good oil condition?

I could spend time discussing the merits of additional filters such as pressure or kidney loop systems. Or even discuss element types and beta ratios, but there is an often overlooked practice that is just as important to consider in a good PM program than just changing elements: Oil Sample Analysis.

Taking oil samples and sending them in for analysis is a tremendous proactive tool to ensure your oil condition is favorable to prevent down time from component failure. Sample kits are available from a number of sources including your oil supplier or your local hydraulic filter distributor. The kits are usually just a plastic bottle you use to ship your sample in for analysis. The cost of the bottle also includes the cost of the analysis.

A sample analysis report should provide you the following about the condition of the oil:

  • Particulate Levels- You will get the ISO code for the level of particulate matter floating through your system. The ISO code should be reviewed against the type of components in your system to make sure your oil is clean enough for your most picky component. The particulate levels become extremely important in servo systems, but particulates can cause trouble in any system.
  • Water Content- Perhaps even more damaging than the particulate, too much water content can accelerate the effects of particulates and create more particulates through corrosion. Most pumps use the hydraulic fluid in the system to lubricate bearings and just .05% water content is enough to reduce bearing life by 50% according to a 1986 study by Timken Bearing. The oil sample analysis will catch to much water content well before you get the visual evidence of milky looking oil.
  • Particulate Content- Quality sample reports also will offer details of what particulates are in the oils. If given the brand and type of fluid in your system the analysis can compare the wear metal additives of your oil to a base line sample from the oil manufacturer. In addition to ensuring the condition of the oil additives, the particulate make up can give you insight on components that are showing signs of excessive wear.

A properly managed sample program can make these reports even more useful. Regular submitted samples allow your Analysis provider to create trending charts on the condition of your fluid. These can help you fine tune your filtration program and perhaps even allow you to schedule proactive maintenance on pumps or cylinders that are showing signs of wear by emitting metals into the system.
If you want further information contact your oil supplier or your vendor for hydraulic filters. Also I find the Parker’s Handbook of Hydraulic Filtration a good reference that remains more educational than marketing. The handbook can be found on their website at Parker.com.

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