The heart of every hydraulic filter is the filter element, which is installed in the filter housing. This is always the case, regardless of 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 construction and agricultural machinery.
Hydraulic filter elements are available with various filter media. The most prevalent materials are cellulose, glass fiber, wire cloth, and water-absorbing media. A flood of innovative new products in the field of filter media – such as #absolutebeta, FILTREC’s current top-shelf filter medium – are delivering continuous improvements in the areas of pressure drop, dirt retention capacity, service life, operating costs, and environmental friendliness.
The required filter fineness is partially determined by the more vulnerable system components, such as the valves. The manufacturers of these delicate components specify the required oil purity classes to ensure fault-free, low-wear operation. Hydraulic filter elements are used in low, medium, and high-pressure applications (up to 420 bar). There are also non-pressurized variants that are installed in the hydraulic reservoir. Hydraulic filter elements are typically rated to withstand a maximum differential pressure of 210 bar. The standard sealing medium is NBR.
Types of hydraulic filter elements
Cellulose media
Previously, hydraulic filter elements containing cellulose media were commonly used in simple hydraulic systems. The filtration fineness of these filter elements is typically 10 µm or 25 µm; however, their filtration efficiency is far lower than that of filter elements containing glass-fiber media. For this reason, the growing trend in recent years has been to use glass-fiber filter media wherever possible.
Glass-fiber media
Hydraulic filter elements with a glass-fiber medium are mostly used in hydraulic systems whose components, e.g., proportional valves, variable displacement pumps and servo valves, require maximum protection against contamination. In contrast to cellulose media, hydraulic filter elements containing a glass-fiber medium are available with a much higher filter fineness and are characterized by high efficiency and a large dirt-removal capacity. Another advantage is their high differential-pressure stability up to 210 bar, which cannot be achieved with a cellulose medium.
Hydraulic filter elements with a wire mesh
Hydraulic filter elements containing a wire mesh are mainly used as protective filters upstream of the pump, where they function as a so-called suction filter. These hydraulic filter elements are characterized by their ability to withstand pressure surges and their resistance to water and acids. The filter fineness is typically 25 µm, 60 µm or 125 µm.
Water-absorbing filter media
Hydraulic filter elements containing water-absorbing filter media are used to remove water from the oil in addition to their main task of filtering the hydraulic oil. By means of a 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 due to system-related temperature differences.
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