@Air Compressor

2025-03-30

Differences between oilless screw compressors and oil-filled screw compressors

Oil-free screw compressor and oil-filled screw compressor are the two major branches of screw compressor. The core difference is thatlubrication method, which in turn affects performance, application scenarios and maintenance requirements. The following is a specific comparison:

1. working principle

oil-filled screw type：
By lubricating the rotor by injecting oil, the oil film simultaneously plays the role of sealing, cooling and noise reduction. After mixing the lubricating oil with compressed air, it needs to be filtered by an oil separator to ensure that the oil content of the exhaust gas is ≤3ppm.
oil-free screw：
Use self-lubricating materials (such as special coatings or ceramics) or forced gas lubrication to avoid oil contamination. Some models reduce friction through water cooling or optimized screw design.

2. Core performance differences

indicators	oil-filled screw type	oil-free screw
efficiency	Higher (oil lubrication reduces friction)	Slightly lower (relying on material self-lubrication)
noise	Low (oil film buffer)	Higher (additional noise reduction design is required)
life	Long (adequate lubrication)	Shorter (material wear limit)
maintenance	Regularly change oil and check separators	No oil management required, but temperature monitoring required

3. application scenarios

oil-filled screw type：
- Manufacturing (such as pneumatic tools, painting), chemicals (gas transportation), energy (natural gas pressurization).
- Scenes with low requirements for air cleanliness.
oil-free screw：
- Medical (breathing gas), food (packaging inflation), electronics (chip manufacturing).
- Special processes contaminated by oil are prohibited (such as textile spray dyeing, laboratories).

4. cost comparison

initial investment: Oil-free models are usually 30%-50% expensive due to complex technology.
long-term cost：
- The oil-filled model requires oil costs, filter element replacement, etc.(the annual cost is about 5%-10% of the equipment price).
- Oil-free models are easy to maintain, but fault repair costs are high.

5. technology trends

oil-filled screw type: Develop towards higher pressure (>1MPa) and lower noise (<65dB).
oil-free screw: Develop new lubricating coatings (such as DLC diamond coatings) to improve efficiency to close to the oil-injecting type.

Selection suggestions

preferably selectedoil-filled screw type: If continuous high-load operation is required and is insensitive to oil content.
must chooseoil-free screw: When compressed gas comes into direct contact with the product, or when regulations prohibit oil residues (such as ISO 8573-1 Class 0 standard).

The two technologies have their own advantages and disadvantages, and comprehensive decisions need to be made based on actual working conditions (such as operating environment, maintenance capabilities, and budget).

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