Short Answer: Hydraulic filters should not be changed according to a universal time interval. Donaldson Hy-Pro recommends monitoring differential pressure and hydraulic fluid cleanliness, and considering filter type and efficiency to determine when replacement is necessary.
Knowing when to change a hydraulic filter is an important part of maintaining hydraulic system cleanliness. However, there is no single replacement interval that works for every system.
The right time to replace a filter depends on indicators such as differential pressure, ISO cleanliness codes, and filter type.
Not necessarily.
Changing a filter based only on a calendar schedule can result in replacing an element before it is fully utilized, or leaving one in service after it has become heavily loaded.
A better approach is to measure the differential pressure across the filter and monitor the cleanliness of the hydraulic fluid based on the ISO Code targets established for the actual hydraulic components being used in the system.
As hydraulic fluid passes through the filter, the element captures contaminants. Over time, those contaminants accumulate in the filter media and can increase the filter’s differential pressure.
Monitoring differential pressure across the filter can therefore help indicate when an element is becoming loaded and requires attention. Temperature, viscosity, and flow conditions can also influence pressure drop.
Yes.
The amount and type of contamination entering a hydraulic system can vary significantly depending on the application, operating environment, maintenance practices, and other factors.
Regular oil sampling and cleanliness monitoring can help track contamination trends using particle counts and ISO 4406 cleanliness codes. This information can show whether the system is maintaining the ISO Code target appropriate for the hydraulic components being used and whether the overall filtration strategy is effectively controlling contamination.
If cleanliness codes are unstable or out of target range, the solution may not simply be to replace filters more frequently. The source of contamination and the filtration strategy may also need to be evaluated.
The type of filter element you choose can affect how effectively contamination is removed from the hydraulic fluid. Different media, such as microglass and cellulose filter media, can have different performance characteristics, including their ability to capture particles from the hydraulic fluid.
Filter efficiency is one of the key factors to consider when selecting a filter element. Beta ratio is commonly used to describe an element’s efficiency at removing particles of a specific size under controlled, steady-state multi-pass test conditions.
However, laboratory test conditions do not always represent what happens in an operating hydraulic system. Hydraulic systems can experience changing and cyclic flow conditions that can affect filter performance. Dynamic Filter Efficiency (DFE) can provide insight into how a filter element performs under these dynamic operating conditions.
An element can demonstrate a high Beta ratio under controlled, steady-state testing, while its performance under cyclic flow conditions may be different. A filter that has been DFE tested can provide a more complete understanding of performance.
There is no universal filter-change interval for hydraulic systems.
Instead, consider:
Using this information together can help maintenance teams make more informed decisions about when to replace a filter element and when broader changes to the contamination control strategy may be needed.
There is no standard schedule for changing a hydraulic filter.
Monitoring differential pressure can help determine how loaded the filter element has become, while oil sampling and ISO 4406 cleanliness codes can show whether the hydraulic fluid is meeting the cleanliness target for the system’s components. Filter type, media, Beta ratio, and DFE performance can also affect how effectively contamination is controlled.
Considering these factors together can help maintenance teams avoid unnecessary filter changes while maintaining the cleanliness needed for reliable hydraulic system operation.
Q: How often should a hydraulic filter be changed?
A: There is no universal filter-change interval. The appropriate replacement frequency depends on factors such as contamination levels, operating conditions, filter condition and pressure drop.
Q: Can you change a hydraulic filter too often?
A: Yes. Replacing a filter solely according to a fixed schedule may result in replacing an element before it needs to be changed. This can add unnecessary filter and maintenance costs without providing a corresponding benefit. Monitoring differential pressure and fluid cleanliness can help support a more informed replacement strategy and avoid unnecessary filter changes.
Q: What indicates that a hydraulic filter needs to be changed?
A: Increasing differential pressure across the filter can indicate that an element is becoming loaded with contamination. Oil cleanliness data and contamination trends can also provide useful information about filtration performance.
Q: How does oil sampling help with filter maintenance?
A: Oil sampling can help monitor particle contamination and track changes in hydraulic oil cleanliness over time. This information can be used alongside filter condition data when making maintenance decisions.
Q: Why is hydraulic oil cleanliness important when determining filter changes?
A: The purpose of hydraulic filtration is to control contamination and maintain the desired level of fluid cleanliness. Monitoring cleanliness can help determine whether the existing filtration strategy is effectively controlling contamination.
About Donaldson Hy-Pro:
Donaldson Hy-Pro offers a wide range of hydraulic filtration solutions that can help you improve the performance of your machinery. Our filter elements are designed to combat dirt, water, and oxidation by-products, to help keep your systems running at peak performance.
If you're looking for a way to reduce filter expenses, improve oil cleanliness, and extend the life of your equipment, Donaldson Hy-Pro can help. Contact us today to learn more.