Causes Of Contamination in Excavator Hydraulic Oil

Writer： Kaiqian Oil Purifier Release time：2025-11-03 16:43 Clicks：

I. Main Causes of Hydraulic Oil Contamination
1. External Contaminants

• Improper refueling methods: Pouring oil directly from a bucket introduces dust from the air and impurities from the bucket walls.
• Dirty maintenance environment: Disassembling hydraulic lines, cylinders, pumps, or valves in a windy, dusty, and open-air environment can cause contaminants to enter the system.
• Replacing hydraulic accessories: When replacing hydraulic components, machining chips and cleaning fluid may remain inside the new component. Installing the new component without thorough rinsing can contaminate the entire tank of new oil.
• Damaged or ineffective hydraulic cylinder dust seals: If the dust seal is damaged, retracting the piston rod will introduce dust and moisture directly into the hydraulic system.
• Damaged or clogged tank breather: A clogged breather creates negative pressure in the system, damaging the seal. A failed breather filter allows airborne dust to be drawn directly into the tank.
• A leaky oil tank cap or dirty dipstick: When checking the oil level, dirt on the dipstick or oil tank cap can also be introduced.

2. Internally Generated Contaminants

• Normal Wear: Moving parts such as hydraulic pumps, motors, and cylinders generate tiny metal wear particles during normal operation.
• Abnormal Wear: Rapid wear of components due to oil contamination, improper oil selection, or prolonged overload operation generates large amounts of iron and copper shavings.
• Oil Oxidation and Deterioration: Hydraulic oil oxidizes under high temperatures and air, producing viscous sludge such as colloids and asphalt. This sludge can clog filter elements and cause valve clearances to become restricted.
• Moisture Intrusion and Rust: If moisture enters the system (via breather condensation, water immersion, etc.), it can cause rust on the inside of the oil tank and pipes, generating rust particles.

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3. Improper Maintenance

• Filter Element Replacement Expiration: If a filter element is not replaced for an extended period, its filtration capacity becomes saturated, making it unable to absorb impurities. It may even become damaged due to excessive pressure differentials, releasing previously filtered impurities back into the system.
• Using Low-Quality Filter Elements: Low-quality filter elements fail to meet filtration standards and are unable to protect the system effectively.
• Exceeding the Hydraulic Oil Lifespan: Hydraulic oil has a limited lifespan. After this lifespan, its lubricating, rust-proof, and antioxidant properties decline dramatically, leading to internal wear and increased sludge, creating a vicious cycle.
• Mixing Hydraulic Oils: Hydraulic oil additives with different formulations may chemically react, resulting in precipitation and oil deterioration.

II. Prevention and Resolution

1. Control External Contaminants

• Maintain Clean Fueling: When refueling, use a dispenser equipped with a high-precision filter; do not pour directly from a bucket.
• Maintain Sealing: Regularly replace the fuel tank air filter to ensure it is in good condition and prevents the ingress of airborne dust. Promptly replace damaged cylinder piston rod dust seals.
• Maintain Cleanliness During Maintenance: When disassembling or repairing hydraulic components, seal all openings with plastic caps or tape to prevent the ingress of debris.

2. Control Internal Contaminants

• Regular Filter Inspection and Replacement: Strictly follow the equipment maintenance manual and regularly inspect and replace the hydraulic system's suction, pressure, and return filters.
• Regular Oil Analysis: Sampling and analyzing hydraulic oil can identify wear and contamination issues in advance, enabling predictive maintenance and avoiding unexpected failures.

3. Control Contaminants Generated During System Operation

• Control Oil Temperature: Avoid prolonged high oil temperatures that accelerate oil oxidation and deterioration, forming sludge and gum.
• Prevent Water Intrusion: Regularly inspect the bottom of the oil tank and drain any accumulated water promptly.

4. Purification and Filtration

• If the oil is slightly contaminated, a portable hydraulic oil filter (with a high filtration accuracy) can be used. 5-10μm) circulating filter oil in the tank removes existing impurities and extends oil life.
• If water mixes with the oil, causing it to emulsify, drain the accumulated water at the bottom of the tank. A hydraulic oil vacuum filter is suitable for this application. It can quickly remove liquid water, free water, and dissolved water from the oil, while also removing gaseous and solid impurities, restoring key hydraulic oil properties such as viscosity and flash point, ensuring the normal operation of the hydraulic, power, and lubrication systems.