Water-injected Oil-free VS Dry Oil-free Screw Air Compressor

Water-injected Oil-free VS Dry Oil-free Screw Air Compressor

(05/09/2021 - Lượt xem: 330)

In recent decades, there has been more and more research on the oil-free screw air compressor. According to the type of lubrication, the Screw type air compressor has two kinds: the water-lubricated single-screw type and the dry twin-screw type.

For the Dry oil-free screw air compressor, most are twin-screw air compressors. Water-lubricated oil-free screw air compressor is also called a water-injected screw air compressor, most are single screw air compressors. The following analyze their differences:


Water-injected Oil-free

Single Screw Air Compressor


Dry Oil-free

Double Screw Air Compressor

Working Principle


Water-lubricated Oil-free Single Screw  Dry Oil-free Double Screw 

Air Quality

100% Oil-Free Oil in the gear

Air Purity

Clear air after purified by water Contain dust and oil stain

Lubrication Media

Pure Water Dry

Air Temp

 Less than 55℃ About 180~200℃


Single-Stage Two-stage

Cooling method

Don’t need a cooling system Need interstage and after Cooling system


Simple and Balanced Structure Radial load is not balance

Vibration and Noise

Low vibration and noise High-frequency noise due to the two screws


Ideal Rotation speed 3000r/min, theoretically zero loads.


Long lifetime of the screw (30000h) and star wheel (50000h)

Rotation speed 18000r/min, high loads on screws.


The short lifetime of the screw (8000~18000h)


Only air and water filter elements More spare parts

Different principles

  1. The dry oil-free screw air compressor means that the coating on the surface of the rotor teeth will play the role of lubrication and sealing. There is no lubrication medium in the compression chamber. But there is lubricating oil in the gearbox;
  2. But for the Water-lubricated oil-free type means that the water and air are mixed and compressed. Water plays the role of lubricating, sealing, cooling, and denoising

Different Prices

  1. Water-lubricated oil-free type is mostly single-screw air compressors. The price is generally lower than the dry oil-free type. The maintenance cost is also lower. Only air filter elements and water filter elements.
  2. But for the dry oil-free air compressor, except for the spare parts, the coating also needs to be replaced regularly.

Different Losses

  1. Water-injected oil-free single screw type: ideal isothermal compression, no heat loss.
  2. Dry oil-free double screw type: energy lost due to hot air discharge

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