Fine Filtration of Hydraulic Oil

Fine filtration of hydraulic oil offers numerous advantages and has gained increasing importance in the recent past. The most significant argument for fine filtration is the reduction of wear and tear, and consequently, an extension of the service life of the machine or hydraulic system. The prevention of production downtimes should also be emphasized. These two factors result in clear cost reductions. In addition, maintenance intervals are extended, and environmental impact is significantly reduced.

When a new hydraulic system is put into operation, contaminants are present in the system from the outset, which, without adequate filtration, significantly shorten the service life of valves and cylinders. This so-called “initial contamination” largely consists of coarse particles. During operation, various other types of contamination arise. In addition to solid particles, free or dissolved water and undissolved air are considered contaminants. A large part of hydraulic oil contamination can be removed with situation-specific fine filtration.

Contamination

Contamination in the hydraulic system is the main cause of failures and downtimes. Almost 90% of hydraulic system failures are caused by various impurities in the hydraulic oil. Contamination is either already present in the hydraulic system, enters the hydraulic system from outside, or originates within the hydraulic system:

1. Pre-existing contamination:
   

• Contamination in components caused by manufacturing processes (e.g., chips)
• Contamination on components caused by the installation of components

2. Contamination entering from outside:
   

• Filling or refilling the tank
• Damaged tank seal
• Replacement of various components
• Air impurities
• Inadequately sized ventilation/filter system

3. Contamination originating within the hydraulic system:

• Material abrasion in hydraulic units (erosion at points where the hydraulic fluid impacts at high speed)
• High pressure changes or stresses cause coarse particles to break off the surface of hydraulic components
  

Filter Components

Filler and breather filters are mounted on the oil reservoir and thus prevent dirt from the environment from entering during the tank breathing process. The filter fineness must be chosen carefully.

Return line filters are installed in or on the oil tank. They filter the oil before it flows back into the oil tank. Contamination generated in the hydraulic system components is thus filtered out before flowing through the components. These filters, like pressure filters, maintain the oil’s purity class and must be chosen accordingly. However, a return line filter only has to withstand very low pressure.

Return flow distributors ensure that the oil’s return flow calms down before it can enter the oil tank. This prevents foaming and the stirring up of settled dirt.

Suction strainers primarily serve to protect the pump in the hydraulic system. This is particularly important in applications with a high risk of pump damage. They are coarse filters used when the tank can only be serviced with great effort.

Dehumidifiers remove all moisture from the intake air using silica gel.

Offline filters are external units that extract, filter, and return oil to the hydraulic system.

Bypass filters are active only during the operation of the hydraulic system and divert a small volume flow of oil from the hydraulic system for filtration.