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Updated: Jun 11

Piston Air Compressor Oil

1. Function and Requirements:

  • Lubrication and Cooling: Piston air compressors use oil primarily for lubricating the piston and cylinder walls, reducing friction, and helping to cool the compressor. The oil must withstand high temperatures and provide a good seal.

  • Contaminant Handling: Piston compressors can generate more contaminants such as carbon deposits and moisture. The oil must have the ability to handle these impurities and prevent buildup.

2. Characteristics:

  • Viscosity: Typically, piston air compressor oils have higher viscosity to provide a thick lubricating film on the piston and cylinder walls. Common viscosities are SAE 30 or SAE 40.

  • Detergent-Free: Piston compressor oils are usually non-detergent. Detergents can cause carbon deposits to stay suspended in the oil, potentially leading to wear and tear on the components.

  • Thermal Stability: The oil must maintain its lubricating properties at high temperatures, as piston compressors can run quite hot.

3. Types of Piston Compressor Oils:

  • Mineral Oils: Many piston air compressors use mineral-based oils. These are less expensive and provide adequate lubrication for standard-duty cycles.

  • Synthetic Oils: For more demanding applications or higher-duty cycles, synthetic oils offer better thermal stability, lower volatility, and longer service life.

Rotary Screw Air Compressor Oil

1. Function and Requirements:

  • Lubrication, Cooling, and Sealing: Rotary screw air compressors use oil to lubricate the screws, cool the compressed air, and provide a seal between the screws and the housing to ensure efficient compression.

  • Heat Dissipation: The oil in rotary screw compressors plays a significant role in dissipating heat generated during compression. The oil is constantly circulated through a cooler to manage the temperature.

2. Characteristics:

  • Viscosity: Rotary screw compressor oils generally have lower viscosity compared to piston compressor oils, as the oil must flow easily through the system and cool effectively. Typical viscosities are ISO 32, ISO 46, or ISO 68.

  • Additives: These oils often contain additives to prevent oxidation, corrosion, foaming, and wear. Additives help maintain oil performance over extended periods and under continuous operation.

  • Thermal Stability and Oxidation Resistance: Rotary screw compressor oils need to resist oxidation and thermal breakdown over long operating cycles to prevent the formation of sludge and varnish.

3. Types of Rotary Screw Compressor Oils:

  • Mineral Oils: Suitable for standard applications with moderate duty cycles. They provide good lubrication and cooling but may require more frequent changes.

  • Synthetic Oils: Ideal for continuous or heavy-duty operations. They offer superior thermal stability, longer service intervals, and better overall performance.

Key Differences

  1. Viscosity:

  • Piston Compressors: Use higher viscosity oils (e.g., SAE 30 or SAE 40) for better lubrication of pistons and cylinders.

  • Rotary Screw Compressors: Use lower viscosity oils (e.g., ISO 32, ISO 46) for efficient flow and cooling.

  1. Detergents:

  • Piston Compressors: Typically use non-detergent oils to avoid keeping contaminants in suspension.

  • Rotary Screw Compressors: Use oils with additives to handle contaminants and maintain performance.

  1. Thermal Stability:

  • Piston Compressors: Require oils that can handle high temperatures due to the intermittent and high-pressure nature of their operation.

  • Rotary Screw Compressors: Require oils that can maintain stability and prevent oxidation over continuous, high-duty cycles.

  1. Additives:

  • Piston Compressors: Usually have fewer additives, focusing on lubrication and basic protection.

  • Rotary Screw Compressors: Contain advanced additives for oxidation resistance, anti-wear, anti-foaming, and corrosion protection.


The primary differences between piston air compressor oil and rotary screw air compressor oil lie in their viscosity, additive content, thermal stability, and specific functions tailored to the operational demands of each compressor type. Using the correct oil for your air compressor is crucial for maintaining its performance, efficiency, and longevity. Always refer to the manufacturer’s recommendations for the appropriate oil type and change intervals to ensure optimal compressor operation.

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