Function of hydraulic filter elements

The heart of every hydraulic filter is the filter element installed in the filter housing. It does not matter whether the hydraulic filter elements are used in a stationary application such as hydraulic presses, plastic injection molding machines or in mobile applications such as in construction and agricultural machinery.

Hydraulic filter elements are manufactured with different filter media. The most important filter media are cellulose, glass fiber, wire mesh or water-absorbing media. Through constant new developments of filter media, such as the ultimate filter medium #absolutebeta from FILTREC, ever better results are being achieved in the areas of pressure loss, dirt holding capacity, service life, operating costs and environmental friendliness.

The filter fineness is determined based on the sometimes sensitive system components, such as valves. The manufacturers of these sensitive components specify the required oil cleanliness classes to ensure trouble-free and low-wear operation. Hydraulic filter elements are used in the low, medium and high pressure range (up to 420 bar) as well as in the tank as an unpressurized version. The usual differential pressure resistance of hydraulic filter elements is up to 210 bar. The standard sealing medium is NBR.

Types of hydraulic filter elements

Cellulose medium

Hydraulic filter elements with cellulosic media have hitherto been used in simple hydraulic systems. The usual filter fineness of these filter elements is 10 µm or 25 µm, but they have a significantly lower efficiency compared to a filter element with a glass fiber medium. Therefore, in recent years, there has been an increasing trend towards equipping as many filter elements as possible with a glass fiber medium.

Fiberglass medium

Hydraulic filter elements with glass fiber media are mostly used in hydraulic systems whose components, such as proportional valves, variable displacement pumps or servo valves, require maximum protection against contamination. In contrast to the cellulose medium, hydraulic filter elements with a glass fiber medium can achieve significantly better filter fineness with a high level of efficiency and a large dirt holding capacity. Another advantage is the high differential pressure stability of up to 210 bar, which cannot be achieved with a cellulose medium.

Hydraulic filter elements with wire mesh

Hydraulic filter elements with wire mesh mostly serve as a protective filter in front of the pump as a so-called suction filter. These hydraulic filter elements are characterized by high stability against pressure surges and good compatibility with water and acids. The common finenesses are 25 µm, 60 µm or 125 µm.

Water absorbing filter media

Hydraulic filter elements with water-absorbing filter media offer the possibility of absorbing water from the oil in addition to the actual task of filtering the hydraulic oil. Due to the special filter medium, these elements can convert the water into a gel and thus remove it from the oil circuit. These filter elements are used in hydraulic systems in which condensation occurs in the hydraulic system due to system-related temperature differences.