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Hydraulic oil filtration requirements are a critical and systemic issue, directly impacting the reliability, efficiency, and component life of hydraulic systems. The following content will detail the requirements for hydraulic oil filtration and key considerations.
The core goal of hydraulic oil filtration is to control oil contamination, specifically maintaining the number of solid particles in the oil within the system's acceptable range. This is primarily reflected through the following key indicators:
This is the most important metric, indicating the minimum particle size that a filter can effectively capture. It is typically expressed as either absolute or nominal.
Absolute Filtration Rating (μm): This refers to the minimum particle size that a filter can effectively remove 100%. This is a more stringent and reliable indicator. For example, a filter with an absolute filtration rating of 10μm is guaranteed to remove all particles 10μm or larger.
Nominal Filtration Rating (μm): This indicates the percentage (usually 90%-98%) of particles of a specific size that a filter can remove. This indicator is less reliable than the absolute filtration rating.
General Recommendations:
High-pressure, high-precision systems (>21 MPa, servo valves, proportional valves): These systems are extremely demanding, typically requiring ISO 14/12/10 or higher cleanliness levels. Recommended main filter absolute filter accuracy is 3-5 μm.
Medium-to-high-pressure systems (14-21 MPa, vane pumps, plunger pumps): High requirements, targeting cleanliness levels of ISO 16/14/11, with a recommended main filter absolute filter accuracy of 5-10 μm.
Medium-to-low-pressure systems (<14 MPa, gear pumps): Moderate requirements, target cleanliness levels of ISO 18/16/13, and recommended main filter absolute filter accuracy is 10-15 μm.
This is an internationally recognized standard for measuring the degree of oil contamination, typically using ISO 4406:2021. It is represented by three numbers, such as 18/16/13, representing:
First number: Particle count range ≥ 4μm per milliliter of fluid.
Second number: Particle count range ≥ 6μm per milliliter of fluid.
Third number: Particle count range ≥ 14μm per milliliter of fluid.
The lower the number, the cleaner the fluid. Determining the manufacturer's recommended cleanliness level for your hydraulic components (especially the most sensitive components, such as servovalves) is fundamental to setting filtration goals.
This is a measure of filter performance effectiveness.
βₓ = Number of particles larger than xμm in the upstream fluid / Number of particles larger than xμm in the downstream fluid.
For example, a β₁₀ = 1000 means that for every 1000 particles of 10μm passing upstream, only one particle will pass downstream. The filtration efficiency of this filter is (1000 - 1) / 1000 = 99.9%.
βₓ ≥ 2: Filtration efficiency > 50%
βₓ ≥ 75: Filtration efficiency > 98.7%
βₓ ≥ 200: Filtration efficiency > 99.5% (commonly known as a high-efficiency filter)
When selecting a filter, focus on the β value relative to absolute accuracy; the higher the β value, the better.
Hydraulic oil filtration is a systematic process that requires:
Target Setting: Determine the target cleanliness level (ISO code) and required filtration accuracy based on system pressure and the requirements of the most delicate components.
Rational Configuration: Optimally place filters in the suction, pressure, and return lines. Consider adding bypass filtration for critical systems.
ｓｅｌｅｃｔ Quality Products: Use high-beta, high-quality brand-name filter elements.
Scientific Maintenance: Regularly test the oil to monitor its condition; promptly ｒｅｐｌａｃｅ filter elements; and strictly prevent the ingress of external contaminants.
Comprehensive Management: Filter not only solid particles but also water and air contamination.
Following these requirements and recommendations can significantly extend the service life of hydraulic oil and components, reduce downtime, and ultimately improve the overall efficiency of your equipment.
