Dirt capacity has become a widely used rating factor for filters because it seems easy to measure and understand. It is often used to predict filter service life or to compare filters. Unfortunately, dirt capacity alone is of little value in estimating filter service life or in comparing the relative service lives of competing filters. Realistic estimates and comparisons can be made only when test conditions, filter efficiency ratings, and details of field operating conditions where the filter will be applied are known.

When selecting long-life hydraulic or lubricating filters, the primary concern should always be the filter efficiency. Filters must be capable of adequately removing and controlling particles equal to or slightly larger than the clearances in critical system components. Then the filter should be sized to provide adequate element service life. Higher efficiency filters produce lower contaminant levels and less component wear. Thus, more efficient filters can provide longer element service life than coarse filter elements with similar or higher dirt capacity ratings.

Selecting Long-Life Filters - Cautions in Using Dirt Capacity