Hydraulic Fluid Contamination – What You Need to Know?


In a variety of industrial settings, hydraulic systems play a pivotal role by energizing machinery and guaranteeing the efficient execution of operations. However, maintaining the integrity of hydraulic systems requires a comprehensive understanding of fluid contamination. In this article, we will explore the various facets of hydraulic fluid contamination, ranging from built-in contamination, air and water contamination, to contamination by foreign objects. We will also discuss effective methods for removal of causes of contamination.

What is the function of lubricants in hydraulic systems?

The efficient and trouble-free operation of construction machinery and equipment utilizing hydraulic systems depends, among other factors, on the quality and condition of hydraulic fluid. Hydraulic fluid serves to transfer power within high-pressure hydraulic systems, facilitating the smooth functioning of excavator winches, hydraulic brakes, and power steering systems.

Another lubricant that ensures the long and reliable operation of components in construction machinery, such as track excavator final drives, is gear oil. This reduces friction generated during the operation of a planetary gearbox between its individual components and dissipates heat from critical areas within the neuralgic/ critical system components.

Fluids used for operating various types of machinery and equipment must be free from contaminants to effectively fulfill their functions. Therefore, conducting regular inspections of utilized machines and adhering to manufacturers’ recommendations regarding the selection of spare parts is crucial.

What are the types of hydraulic fluid contamination?

Hydraulic fluid contamination can occur, for example, due to the breakdown of seals or as a result of the wear and tear of machine components during operation. Regardless of the type of contamination, it is important to promptly replace the contaminated hydraulic fluid in the system to ensure efficient and trouble-free operation of the equipment.

Contamination by Chemicals

If hydraulic fluid is exposed to excessive temperature or pressure, it may undergo faster degradation. As the hydraulic fluid approaches the end of its service life, it breaks down into other chemical substances that negatively impact the hydraulic system. Therefore, during maintenance, when adding fresh oil, it is essential to determine the next replacement date according to the manufacturer’s recommendations.

It is also not advisable to mix hydraulic fluids. Each lubricant has its unique properties and operating parameters. The use of different types of fluid, each containing diverse additives, can lead to chemical reactions and, consequently, result in contamination of the hydraulic system.

Contaminants resulting from the operation of machinery

Individual components of excavators or loaders, due to the nature of construction work, undergo significant stresses. A common cause of high levels of contamination in hydraulic fluids is the presence of metallic particles from moving elements of the hydraulic system, detaching from various connections and surfaces. It is not possible to effectively shield against such contaminants, and it is recommended to regularly conduct technical inspections and use appropriate filters.

Hydraulic fluid contamination by the air

If your hydraulic fluid exhibits a foamy appearance, it could indicate contamination with air, which is detrimental to the hydraulic fluid. The existence of air within the hydraulic fluid may result in problems related to compressibility. A significant level of air contamination has the potential to impact the overall efficiency of your machinery, affecting factors such as the torque output from the final drive and the cycle time for your attachments.

To minimize the risk of air contamination, it is essential to adhere to a straightforward guideline: avoid unnecessary exposure of your hydraulic system to air, and refrain from leaving hydraulic fluid storage containers open without a specific reason.

Water contamination

Water contamination can present challenges for your hydraulic fluid. If the oil shows bubbling or sizzling, it signifies an excessive level of water within the oil, which is not acceptable. It impacts compressibility, induces corrosion problems, hinders the hydraulic fluid’s lubricating capabilities, and contributes to sludge formation. In addition, water-contaminated hydraulic fluid can result in cavitation in the pump of your machine, leading to potentially costly repairs or replacements.

If your fluid appears milky, it is likely an indication of water contamination. Through “breathing,” which happens when a container is exposed to a wide variety of temperatures, moisture can get inside waterproof containers. Remember to keep unused hydraulic fluid securely stored in sealed containers, and always placed on their sides.

Build in Contamination

Every recently manufactured machinery and its components, including but not limited to final drive motors, hydraulic motors, pumps, etc., will inherently contain some level of initial contamination. Built-in contamination refers to impurities present in hydraulic fluid from the outset. These contaminants can stem from hydraulic fluid production processes, storage conditions, or improper handling. Addressing built-in contamination is essential for preserving the longevity of hydraulic systems and the efficiency of their components.

Hydraulic Fluid Contamination by Foreign Objects

The presence of solid contaminants such as dirt, dust, or debris in hydraulic fluid can also be a cause of malfunction or failure in the hydraulic system. These impurities can easily enter hydraulic systems during routine inspections or as a result of leaks. Before commencing with the maintenance of the machine, it is crucial to start by cleaning the equipment from accumulated mud and dust to minimize the risk of hydraulic fluid contamination. The servicing of the device itself should be carried out in the most sterile conditions possible.
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How to Remove Contaminants from Hydraulic Oil?

Contaminated hydraulic fluid should be filtered using specialized filtration equipment. This procedure will restore the working fluid to its original technical parameters, allowing it to effectively protect our machinery. The hydraulic oil filtration process, depending on the contamination level of the fluid, takes approximately 2 to 4 hours.

To effectively prevent the infiltration of undesired elements into hydraulic oil, hydraulic filters are employed. These filters are designed to capture various types of solid and chemical contaminants. These include suction, pressure, and return filters, among others.


Understanding the various types of hydraulic fluid contamination is crucial for preserving the health and efficiency of hydraulic systems. Regular maintenance, moisture control, and proactive filtration are key strategies to prevent and address contamination issues. By following these practices, operators and maintenance experts can ensure the optimal performance and extended lifespan of hydraulic systems in diverse industrial settings.


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