Filter Unit

Filter units are used for the filtered filling and draining of lubricating and hydraulic oils. In addition to these functions, a filter unit can also be used for bypass filtration or unfiltered pumping. High-quality filter units often feature a function for monitoring contamination with solid particles in the oil. These functions are utilized in the following work processes:

• Filling of hydraulic units
• Filtration of mineral oil in hydraulic units in bypass mode
• Transfer pumping with or without simultaneous filtration
• Flushing of small hydraulic units during commissioning of the hydraulic system

Filter units are typically very small, compact, and lightweight, as the use of such a filter device with a portable service unit is considerably more flexible. Additional fundamental requirements for such a portable filter unit include, in addition to the compact design, low wear, long oil service life, and extended change intervals.

Conventional Filter Unit and Its Components

The following section explains the components of a portable filter unit and their functions. In addition to the core component of the filter unit—the pump—the electric motor is the most important element of a filter unit. In most cases, a vane pump with an operating pressure of approximately 3.5 bar up to a maximum of 4.5 bar is used.

Filter Unit: Vane Pump

A vane pump or rotary vane pump consists of a hollow cylinder, the so-called stator, in which an additional cylinder, the so-called rotor, rotates. This type of positive displacement pump is particularly suitable for gaseous or liquid media for pressure or suction applications. The rotor of a vane pump contacts the inner wall of the stator precisely between the inlet and outlet openings. The axis of rotation of the rotor is arranged eccentrically to the stator. The contact point on the inner wall of the stator represents the separation point between the pressure and suction chambers of the pump.

Colloquially, this type of pump is often referred to as an oil pump, as vane pumps have a very high lubricating oil requirement due to the vacuum principle. These pumps are characterized by low costs and very high efficiency in continuous operation. Immediately adjacent to the rotating electric motor are the connection components for the hydraulic circuit: connection head, suction strainer, and the filter element. Other significant components of a filter unit include the contamination indicator for units with continuous monitoring of oil cleanliness during cleaning, the strap wrench, the base, the oil pan, and the pressure and suction lances.

Filter Unit: Electric Motor

The electrically operated drive motor can be powered by compressed air as well as direct or alternating current, depending on the design. On the terminal box of the electric drive motor, there is an on/off switch with a motor protection relay against overload. Special features of this type of electric motor include a pressure relief valve between the pressure and suction sides of the pump for protection against overload. An appropriate limit opening pressure would be 3.5 or 4.5 bar.

What Are the Benefits of Using a Filter Unit?

Advantages of long-term use of a filter unit include a significant increase in oil service life. Furthermore, the service lives of the components and system filters used are also substantially improved. The availability of the connected work machine is increased, as the number of interruptions for changing or cleaning the oil is minimized.

A filter unit is intuitive to operate and very flexible in application due to its compact design. Suction and pressure hoses can be connected to any work machine using adapters. Very good filter units are characterized, among other things, by low noise emissions and lose only minimal performance due to their high efficiency.