What is the function of hydraulic filters?

The main task of hydraulic filters is to select and retain harmful particles (e.g. assembly dirt and abrasion) in the hydraulic fluid of a hydraulic system. Foreign substances damage the hydraulic system twofold:

1. Metallic abrasion and fiber particles can abruptly disrupt the function of hydraulic elements (e.g. by jamming) if they are larger than the smallest occurring gap dimension.
2. Metallic abrasion acts like emery in the oil flow: It therefore leads to rapid wear in hydraulic components. Narrow crevices and sharp deflections are particularly critical.

Practice shows that 80% of all failures of a hydraulic system are due to a contaminated pressure fluid. Hydraulic filters can be used to ensure the purity of the hydraulic oil over a long period of time. When the right filtration systems are used, the degree of purity is even improved.

Hydraulic filters are installed in the fluid circuit of hydraulic systems. The hydraulic fluid flows through them. In the process, the harmful particles are retained in the filter element. Which particles are retained depends on the filter fineness. The main characteristics of a hydraulic filter are the filtering efficiency, the pressure resistance and the pressure difference across the filter.

Wiring diagram hydraulic filter

What is the function of hydraulic filters?

Hydraulic filter elements are divided into surface filters, depth filters and magnetic filters. Of course, combinations are also possible.

Surface filter

In surface filtration, the particles are separated directly on the surface of the filter media. The material used for surface filters is fabric of various shapes (e.g. wire mesh, braid mesh, metal edges). As a rule, all pores of approximately the same size are distributed on a surface.

Advantages:

• Accurate, absolute filtering
• small size
• easy cleaning
• no detachment or washing out of filter material particles

Disadvantages:

• Faster clogging of the filter surface
• Higher filter resistance with increasing surface area occupancy
• Expensive

Depth filter

Depth filters consist of compressed fibrous materials (cellulose, plastic, glass, metal fibers). Sintered filters are sintered from metal be ads whose diameter determines the pore size. However, these are only manufactured for small flow rates. In depth filters, the liquid to be cleaned penetrates the filter structure. In the process, the particles to be filtered get caught in the deeper layers of the depth filter.

Advantages:

• Great dirt holding capacity
• Low pressure drop
• low cost

Disadvantages:

• Large construction volume
• poor cleaning possibility
• Filter material particles can become detached

Magnetic filter

In magnetic filters, a strong permanent magnet “attracts” the metallic substances. The hydraulic fluid must flow close to and at low speed past the solenoid. A magnetic filter is usually used as an additional element to the other filter designs.

Structure of a hydraulic filter element

The design of filter elements varies, depending on the manufacturer. In simple paper elements, the filter mats are made without supporting wire mesh. At higher differential pressures, the filter pleats are compressed at the filter elements. Disadvantage: The drainage capacity of the pleated mats is reduced, which means that many pleats remain unused for filtration.

For higher quality filter elements, a multi-layer mat structure is used. This determines the resistance of the elements to pressure peaks and changing volume flows.

The following properties are indispensable for high-quality filter elements:

• Stability against high differential pressures
• Filter ratings for all cleanliness classes
• Large dirt holding capacity
• Long service life
• large filter areas

What types of filters are there in hydraulics?

Hydraulic filters of various types are used in hydraulic systems. These are:

• Suction filter
• Return filter
• Pressure filter
• Filler and breather filter

Hydraulic filter manufacturer

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