Working Principle of Air Compressor Oil Filter

I. Basic Structure of an Oil Filter (Understand the Structure, Understand the Principle)

• Housing: A metal or plastic casing that withstands oil circuit pressure and connects the oil inlet and outlet.
• Filter Element: The core filtration component, mostly made of pleated filter paper/glass fiber filter material (with high precision and large dirt-holding capacity), and some are supported by a metal framework.
• Bypass Valve (Safety Valve): A key protective device that opens automatically when the filter element is severely clogged and the pressure difference is excessively high, allowing oil to pass directly and preventing machine burnout due to oil cut-off.

II. Working Principle (Normal Working Condition + Clogged Condition)

1. Normal Filtration Condition (Core Process)

• Large particle impurities (e.g., metal shavings, carbon deposit lumps) are trapped on the outer surface of the filter element;
• Micro-impurities (micron-level) are adsorbed and retained inside by the fibers of the filter material.
  The filtered clean oil flows out through the oil outlet and is delivered to lubrication points such as the main unit, bearings and gears.
  As impurities accumulate continuously on and inside the filter element, the pressure difference of the oil filter rises gradually.

2. Clogged Protection Condition (Bypass Valve Activation)

• The bypass valve opens automatically, allowing unfiltered oil to pass directly through the bypass channel;
• Purpose: Ensure continuous oil supply and prevent main unit dry friction and seizure due to oil cut-off;
• Note: Activation of the bypass valve means the oil filter has failed. The oil filter must be replaced as soon as possible, otherwise impurities will directly enter the main unit and cause secondary damage.

III. Key Technical Features (Determinants of Oil Filter Performance)

Filtration Precision

• Commonly used in industrial air compressors: 5–10 μm (mainstream), and some high-end models can reach 3 μm;
• Higher precision enables cleaner filtration, but results in greater pressure difference and smaller dirt-holding capacity, so a balanced selection is required.

Dirt-Holding Capacity

• The total amount of impurities that the filter element can hold, which determines the replacement cycle;
• Pleated filter paper has a larger dirt-holding capacity and longer service life than flat filter paper.

Bypass Valve Opening Pressure

• Must match the lubrication system of the air compressor:
  • Excessively low opening pressure: The bypass valve opens before the filter element is clogged, leading to filtration failure;
  • Excessively high opening pressure: The bypass valve fails to open even when the filter element is completely clogged, causing machine burnout due to oil cut-off.

Sealing Performance

• The O-rings/gaskets between the filter element and the housing must be reliable to prevent “short circuit” (unfiltered oil flowing out directly through gaps).

IV. Difference Between Oil Filter and Oil-Air Separator (Easily Confused, One Sentence Distinction)

• Oil Filter: Removes impurities from lubricating oil, protects the moving parts of the main unit, and is installed on the oil circuit;
• Oil-Air Separator: Separates oil mist from compressed air, ensures the exhaust oil content meets the standard, and is installed on the air circuit.

V. Typical Symptoms of Oil Filter Failure (Reverse Verification of the Principle)

• Reduced oil pressure / Increased oil temperature: Clogged filter element → insufficient oil supply → poor lubrication → temperature rise;
• Pressure difference alarm: Models equipped with a pressure difference switch/gauge will trigger an alarm when the pressure difference exceeds the standard;
• Bypass valve activation: Unfiltered oil causes accelerated wear of the main unit and rapid darkening of the oil;
• Abnormal noise / Seizure of the main unit: In extreme cases, the filter element is completely clogged and the bypass valve fails, leading to machine burnout due to oil cut-off.

Summary