Return filters are installed in the return line as in-line filters or on the tank as tank-mounted filters. They can also be integrated into the tank itself. They ensure that the hydraulic fluid returning from the system is filtered before it flows back into the tank. As a result, all dirt particles are filtered out of the hydraulic fluid before they can contaminate the tank.
The right filter size
When selecting the correct filter size, the maximum possible flow rate is a critical factor. This corresponds to the area ratio between the piston and the piston rod in the hydraulic cylinder, which may exceed the flow rate generated by the pumps.
To protect the hydraulic system and the filter elements from excessive back pressure – and to rule out any damage to these components – integrated bypass valves are typically used, which must be adapted to the respective applications.
Application note
To avoid any foaming of the liquid in the hydraulic tank, it is essential to ensure that the liquid outlet from the filter is always below the liquid level under all operating conditions. It may be necessary to install a pipe or flow diffuser in the filter outlet. It should be noted that the distance between the bottom of the tank and the end of the pipe must not be shorter than two to three times the pipe’s diameter.
Types of filter elements
Filter elements for return filters are available with different filter media. In addition to cellulose, which is increasingly being replaced by glass fiber due to the latter’s greater efficiency, wire mesh is also used in some applications.
As a rule, the filter fineness of the return filter must be matched to the pressure line filters in the hydraulic system in order to prevent any dirt and debris caused by wear downstream of the pump from entering the tank.
Return filters can optionally be equipped with an additional ventilating filter to compensate for atmospheric pressure differences in the tank.
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