"We have been filtering used hydraulic oil according to the equipment manufacturer's drain interval of 2,000 hours for continuous use. While this has been a cost-effective measure, my concern is whether it is a good practice. How can we determine how many hours more the filtered oil will perform effectively? Is there any threat of causing damage to the equipment?"

Generally, calendar- or interval-based oil changes are not preferred. Condition-based oil changes typically are much more cost-effective and efficient. Rather than performing an oil change based on a specified number of operating hours, oil changes should be based on the actual condition of the fluid.

Cleanliness and dryness targets must be established based on the equipment's criticality. Once those targets have been set, oil sampling equipment will need to be procured and proper sample procedures adopted.

In addition, oil sampling frequencies should be established and a credible oil analysis laboratory chosen. During the lab selection process, it is important to discuss the appropriate test slate and limits. The table below shows the recommended test slate and limits for a hydraulic system.

The chart below provides an idea of the theoretical life extension based on changes to the cleanliness targets. The horizontal rows are for the current cleanliness code, omitting the 4-micron range. The vertical columns are for the prospective cleanliness code. As you can see from the chart, it is not difficult to achieve two to three times the life extension just by removing particles.

The following chart serves the same function with regard to the dryness targets of the fluid. As indicated, you can receive two times the theoretical life extension by lowering the lubricant moisture levels from 1,000 to 250 parts per million (ppm).

While more information about the type of hydraulic system would be needed to make a definitive recommendation, almost any system will benefit from a kidney-loop filtration system. Whether it is an installed system or a mobile filter cart will depend on the specific application.