A very large proportion of all hydraulic malfunctions or total failures are due to contamination in the hydraulic oil. Particles penetrating from the outside or internal contamination caused by abrasion reduce the quality of the oil and shorten the service life of the hydraulic system. Even with fresh oils, the cleanliness as delivered is often not sufficient for low-wear and thus trouble-free operation. For this reason, an off-line filter system is recommended to support the main filters in sensitive hydraulic systems.