Contaminated oil may cause considerable damage of the components, unplanned downtime and overall system failure. Basic hydraulic systems often operate with simple, coarse 10-micron filters in return lines, while higher capacity systems, which use proportional valves or servo valves require finer filtration (6-micron filters) in combination with built-in pressure and return filters. The manufacturer should specify the type of system and the required cleanness grade. Periodical taking and analysing oil samples by a third-party contractor or an authorized oil testing lab is recommended. Often, a local distributor of hydraulic components may do it or suggest a reliable contractor to perform these services.