Hydraulic oil pollution and prevention measures

According to statistics, 75% of hydraulic system failures are caused by oil contamination. Therefore, preventing hydraulic oil contamination is crucial for ensuring the normal operation of the system.

1. Hazards of Hydraulic Oil Contamination

Hydraulic oil contamination refers to the presence of impurities such as water, air, fine solid particles, and gelatinous substances in the oil. The hazards of hydraulic oil contamination to the hydraulic system are as follows:

Clogging of filters: Contaminated oil can clog filters, making it difficult for the hydraulic pump to draw oil, leading to vibration and noise. It can also block small orifices or gaps, causing valve components to malfunction.
Accelerated wear: Solid particles accelerate component wear, damage seals, and increase leakage.
Reduced lubrication and corrosion: Water and air reduce the oil’s lubricating properties and cause rust. Air in the system can lead to vibration or crawling phenomena.

2. Causes of Hydraulic Oil Contamination

The main causes of hydraulic oil contamination are as follows:

Residual solid particles: During the assembly or maintenance of hydraulic components, solid particles such as sand, metal shavings, abrasives, welding slag, cotton yarn, or dust may remain due to improper cleaning.
Airborne dust: Harsh working environments around hydraulic equipment may contain dust or water droplets in the air. These can enter the system through vulnerable points, such as the extended piston rod of a hydraulic cylinder, the breather hole of the oil tank, or the oil filling port, causing oil contamination.
Generated pollutants: During operation, internally generated pollutants include metal particles, rust, gelatinous substances from degraded hydraulic oil, and peeled-off fragments from coatings or seals.

3. Measures to Prevent Hydraulic Oil Contamination

To extend the service life of hydraulic components, ensure reliable operation of the hydraulic system, and control hydraulic oil contamination within permissible limits, the following preventive measures are commonly adopted in engineering practice:

Minimize External Contamination: During the installation of hydraulic systems and maintenance of hydraulic components, thorough and strict cleaning must be performed, ideally in a dust-free environment. Install filters on any openings of the oil tank that connect to the atmosphere and clean them regularly. When adding hydraulic oil to the tank, use a filter to prevent contamination.
Filter Impurities from the Oil: Install filters at appropriate locations in the hydraulic system to remove impurities from the oil. Regularly inspect, clean, and replace filter elements as needed.
Control Hydraulic Oil Temperature: Prevent the hydraulic oil from reaching excessively high temperatures to avoid oxidation and degradation, which can produce various contaminants. The operating temperature of a hydraulic system should ideally be kept below 60°C, and even lower for machine tool hydraulic systems.
Regular Inspection and Replacement of Hydraulic Oil: Periodically sample and test the hydraulic oil in the system to analyze its contamination level and ensure it remains within the system’s allowable range. If the oil does not meet requirements, replace it promptly.

Analysis and Troubleshooting of Three Abnormal Phenomena in Hydraulic Oil

(1) Abnormal Increase in Hydraulic Oil Temperature

The fundamental reasons for an abnormal rise in hydraulic oil temperature are as follows:

Low Safety Valve Pressure Setting: If the pressure setting of the safety valve is too low, a significant portion of the hydraulic oil flows back to the oil tank through the safety valve. This reduces the efficiency of the hydraulic system, and if the load is excessive, most of the energy is converted into heat in the hydraulic oil, leading to very high temperatures.
Poor Cooling System Performance: Inadequate cooling efficiency in the cooling system causes the hydraulic oil temperature to rise excessively.
Excessive Circulation Frequency in the Oil Circuit: This often occurs due to insufficient oil volume, leading to difficulties in heat dissipation and a subsequent increase in temperature.

(2)Fault Diagnosis and Troubleshooting:

Start with the simplest check, inspect the oil level in the hydraulic oil tank. If the oil level is insufficient, add oil to the standard level promptly. When adding oil, ensure it matches the same grade as the existing hydraulic oil and filter it before use.
If the oil level is adequate, check the oil cooling system for blockages. If air circulation is obstructed, clean the system promptly to ensure proper airflow and enhance heat dissipation. Sometimes, a loose or slipping fan belt can reduce fan efficiency and cooling performance, so inspect and adjust it as needed, replacing the belt if necessary.
If the oil level, cooling system, and fan belt are all functioning correctly, the issue is likely due to the main safety valve’s pressure setting being below the standard value. Adjust the main safety valve’s pressure setting back to the standard value.

(3) Hydraulic Oil Contamination with Impurities Appearing Cloudy

Hydraulic oil contamination typically involves three types of impurities: solid impurities (e.g., debris, solid particles, or solid residues from degraded hydraulic oil), liquid impurities (primarily water, followed by viscous residues from degraded hydraulic oil), and gaseous impurities (mainly air).

If the hydraulic oil exhibits a white cloudy appearance, solid or viscous liquid impurities can be ruled out, leaving water or air as the likely causes. To diagnose, take a sample of the hydraulic oil and drop it onto a hot iron plate. If bubbles appear (indicating water turning into steam at high temperature), the presence of water in the hydraulic oil is confirmed; otherwise, it is due to air contamination.
If water contamination is causing the cloudiness, allow the hydraulic oil to settle for a period, allowing the water to sink to the bottom of the oil tank.