The main function of the filter is to hold back undissolved foreign particles in hydraulic fluid. This makes it an important part of any hydraulic system. The aim of filtering is that
- The wear on moving parts due to foreign particles is reduced and therefore the lifetime of the devices is increased;
- Malfunctions due to blockages in gaps as well jamming of valve control spools and therefore interruptions in operation are prevented;
- The ageing of the hydraulic fluid due to chemical processes as a consequence of contamination is slowed down.
Filtration is more important in oil hydraulics than in water hydraulicsbecause sealing gaps are used more in which hard particles of dirt can become trapped and then damage the moving surface. For this reason the critical particle size for a specific gap is approximately the size of the gap: significantly larger particles remain in front of the gap and significantly smaller particles pass through the gap without damaging its surfaces.
Distinctions are made:
- Based on the operation pressure: suction filter and pressure filter (high-pressure and low-pressure filters);
- Based on the filtration efficiency: filter in main conduit, partial-flow filter and secondary-flow filter;
- Based on the design: surface filter and volume (bulk) filter;
- Based on the installation location: high-pressure filter, return line filter, breather filter, filler filter.