The Importance of Hydraulic Oil Cleanliness for Hydraulic Systems

The cleanliness of hydraulic oil not only affects the working performance of hydraulic systems and the service life of hydraulic components but also directly determines whether the hydraulic system can operate normally. Most failures in hydraulic systems are related to the contamination of hydraulic oil. Therefore, controlling the contamination of hydraulic oil is of utmost importance.

Causes of Hydraulic Oil Contamination

Pre – operation Residuals

During the flushing process before the hydraulic system is put into use, dirt such as molding sand, chips, abrasives, welding slag, rust flakes, and dust in the pipes and hydraulic components of the hydraulic system may not be completely washed away. Once the system starts working, these contaminants enter the hydraulic oil.

External Ingress

External dust and sand particles can enter the hydraulic oil during the operation of the hydraulic system. For example, they can enter through the reciprocating telescopic piston rods or the leaked oil flowing back to the oil tank. Moreover, during maintenance, carelessness can also allow dust and lint to enter the hydraulic oil.

Self – Generated Contamination

The hydraulic system itself continuously generates dirt that directly enters the hydraulic oil. This includes wear particles from metals and sealing materials, particles or fibers shed from filter materials, and gelatinous substances formed by the oxidation and deterioration of the oil due to rising oil temperatures.

Hazards of Oil Contamination

When the hydraulic oil is severely contaminated, it directly affects the working performance of the hydraulic system, leading to frequent system failures and shortening the service life of hydraulic components. The main cause of these hazards is the particles in the dirt.

For hydraulic components, the entry of solid particles can intensify the wear of the sliding parts. They may also block the throttle holes and damping holes in the hydraulic components or cause the spool to get stuck, resulting in hydraulic system failures.

The mixing of water and air reduces the lubricating ability of the hydraulic oil and accelerates its oxidation and deterioration. It causes cavitation, which accelerates the corrosion of hydraulic components and leads to vibrations and crawling in the hydraulic system.

Measures to Prevent Contamination

The causes of hydraulic oil contamination are numerous and complex, and the hydraulic oil itself continuously generates dirt. Therefore, it is very difficult to completely solve the problem of hydraulic oil contamination.

To extend the service life of hydraulic components and ensure the reliable operation of the hydraulic system, it is a more practical approach to control the contamination level of hydraulic oil within a certain limit.

The work of controlling hydraulic oil contamination mainly focuses on two aspects: preventing contaminants from entering the hydraulic system and removing the contaminants that have already entered the system.

Contamination control should be implemented throughout the entire process of design, manufacturing, installation, use, maintenance, and repair of the hydraulic device. The following measures should be taken in practical work to prevent oil contamination:

Pre – use Cleaning

Hydraulic oil can be contaminated during transportation and storage. Although newly purchased hydraulic oil may seem clean, it is actually “dirty”. It must be left standing for several days and then filtered before being added to the hydraulic system for use.

Post – assembly and Pre – operation Cleaning

Hydraulic components must be thoroughly cleaned during the processing and assembly stages. After the hydraulic system is assembled and before it starts operating, it should be thoroughly cleaned. It is best to use the oil used in the system for cleaning. During cleaning, the oil tank must be completely sealed except for the vent hole (with a dust cover), and the sealing parts should have no burrs or flashing.

In – operation Cleaning

Hydraulic oil can be contaminated by the environment during operation. Therefore, every effort should be made to prevent the intrusion of air and moisture. To completely eliminate the intrusion of water, air, and contaminants, a sealed oil tank should be used, and an air filter should be installed on the vent hole to prevent the entry of dust, abrasives, and coolants. Sealing parts and the bladder in the accumulator should be regularly inspected and replaced.

Appropriate Oil Filters

Using appropriate oil filters is an important means of controlling hydraulic oil contamination. Different filtration methods, precisions, and structures of oil filters should be selected according to the requirements of the equipment, and the oil filters and the oil tank should be regularly inspected and cleaned.

Regular Oil Replacement

Before replacing the hydraulic oil, the oil tank must be cleaned once. If the system is very dirty, it can be cleaned with kerosene, and then new oil can be injected after draining.

Temperature Control

Excessively high working temperatures of hydraulic oil are harmful to hydraulic devices. The oil itself will also accelerate oxidation and deterioration, producing various by – products and shortening its service life. Generally, the working temperature of a hydraulic system should be controlled below 65°C, and that of a machine – tool hydraulic system should be controlled below 55°C.