Type and Principle
Air compressors come in various types, each designed for specific applications. Based on their working principles, they can be broadly categorized into three main groups: positive displacement compressors, dynamic (or speed) compressors, and other specialized types. The core idea behind a positive displacement compressor is to reduce the volume of the gas, thereby increasing its pressure. In contrast, dynamic compressors work by accelerating the gas molecules and then converting that kinetic energy into pressure energy, which increases the overall pressure of the compressed air.
Among the most commonly used air compressors are piston compressors, screw compressors, centrifugal compressors, vane compressors, and scroll compressors. Piston compressors use reciprocating motion to compress air, while screw compressors utilize interlocking helical rotors to trap and compress the gas. Centrifugal compressors rely on high-speed rotating impellers to accelerate the air, and vane compressors use sliding vanes within a rotor to compress the gas. Scroll compressors operate using two interleaved spiral-shaped components. Other types like cam, diaphragm, and diffusion pumps are less common due to their specialized applications and smaller scale.
Positive displacement compressors work by directly changing the volume of the gas to increase its pressure. This group includes both reciprocating and rotary types. A reciprocating compressor uses a piston that moves back and forth inside a cylinder to compress the air. On the other hand, a rotary compressor achieves compression through the rotation of internal elements, such as vanes or screws.
Vane compressors are a type of rotary variable displacement compressor. They feature a rotor with sliding vanes that move radially within an eccentrically mounted cylinder. As the rotor turns, the vanes trap and compress the air before discharging it. Liquid-piston compressors are another form of rotary positive displacement compressors, where water or another liquid acts as the piston to compress and discharge the gas.
The Roots compressor is a rotary positive displacement compressor that uses two meshing lobed rotors to trap and move air from the inlet to the outlet without internal compression. In contrast, screw compressors use two interlocking helical rotors to gradually reduce the volume between them, thus compressing the air.
Dynamic compressors, also known as speed compressors, operate by accelerating the gas through rotating blades. This is commonly seen in centrifugal and axial compressors. Centrifugal compressors use impellers to push air outward, creating a radial flow, while axial compressors use blades to push the air along the axis of rotation. Hybrid flow compressors combine features of both, offering a balance between efficiency and performance.
Jet compressors, though less common, use a high-velocity jet of gas or steam to draw in and compress the surrounding air, finally converting the velocity into pressure through a diffuser. For more detailed information on the operation and maintenance of screw air compressors, you can refer to the book "Q & A of the Operation and Maintenance Technology of Screw Air Compressor" published by China Electric Power Press.
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