Working Principle of an Air Compressor
An air compressor is the main component of an air source device. It converts the mechanical energy of a prime mover (usually an electric motor) into gas pressure energy, generating compressed air pressure.
A compressor is a power machine that reduces the volume of gas and increases its pressure, generating a certain amount of kinetic energy. This kinetic energy can be used as mechanical power or for other purposes.
1. Piston air compressor
When the pressure in the cylinder is lower than the outside atmospheric pressure, the outside air under the action of the pressure difference between the inside and outside the cylinder, the tension of the customer service spring pushes the inlet valve and enters the cylinder (at this time, the outlet valve is closed). When the piston moves to the lower dead center, the cylinder is filled with air and its pressure is equal to that of the outside atmosphere. Due to the balance of pressure inside and outside the cylinder, the valve spring bounces back and closes the intake valve, thus completing the suction process.
When the piston moves from the bottom dead center to the upper dead center, the air in the cylinder is compressed because both the inlet and outlet valves are closed. As the piston moves upward, the volume of the cylinder continues to decrease, and the pressure of the compressed air becomes higher and higher. This process is a compression process.
When the pressure of the compressed gas exceeds the combined force of the tension of the valve spring and the pressure in the outlet pipe, the outlet valve is pushed open, and the compressed air is discharged from the outlet pipe until the piston reaches the top dead end. This process is the exhaust process.
When the piston moves from the top dead center to the dead center, fresh air is drawn into the cylinder again, and the next suction process begins. This is how piston air compressors cycle through intake, compression and exhaust.
Remarks: Since the piston air compressor in the low pressure market is initially eliminated by the screw air compressor, we can understand the piston air compressor.
2. Screw air compressor
Screw air compressors are divided into two types: twin screw air compressors and single screw air compressors.1) Working principle and introduction of twin screw air compressor:
The twin screw air compressor is a pair of yin and yang rotors (or screws) meshed parallel to each other in the cylinder, so that the air between the rotor cogging grooves constantly produces periodic volume changes, and the air is transported along the axis of the rotor from the suction side to the output side to realize the whole process of suction, compression and exhaust of the screw air compressor.
2) Working principle and introduction of single screw air compressor:
Single screw air compressors are characterized by only one screw rotor. But in fact, a single screw air compressor has three rotating axes, that is, it consists of a screw rotor and two planetary gears perpendicular to the screw rotor. As a member of the screw air compressor family, the single screw air compressor has similar advantages to the twin screw air compressor, but it has not been promoted on a large scale due to the following problems that are difficult to solve in the industry.
a. There are many moving parts: the single-screw air compressor has three rotating shafts, and the rigidity of the screw and the planetary gear is very different, and it is easy to deform unevenly during movement, so the interlocking accuracy is difficult to guarantee, so the volumetric efficiency is low. In the current market of single-screw compressors in the planetary gears are made of non-metallic materials, the wear resistance is poor, in the process of high-speed work, due to the large wear, resulting in the increase of internal leakage, so the flow rate has a large attenuation after a period of work, generally after 3000 to 4000 hours of operation, the average flow rate attenuates by 5~10%. Therefore, the economy of single-screw air compressors in industrial applications is extremely poor. In addition, the meshing accuracy caused by uneven deformation is difficult to guarantee, and the mechanical stability of the whole equipment will be reduced, so the failure rate is high and the maintenance rate is high, which further limits its scope of use.
b. The material of the planetary gear needs to be further improved. As one of the core components of the single screw compressor, the planetary gear plays a sealing role. If steel planetary gears are chosen, due to the large expansion coefficient of steel and large expansion volume, it is necessary to leave a large gap between the planetary gear and the screw, which not only has many leaks, low efficiency, but is also easy to bite to death and cause major failures: if composite materials are used, although the above problems can be solved, but due to the low strength of the current composite materials, poor wear resistance, under the action of shear force and mechanical friction during operation, not only will it be damaged soon, resulting in increased internal leakage, reduced efficiency, and frequent maintenance, Increase the labor intensity and maintenance cost of maintenance personnel. How to find a material with high strength, low expansion and wear resistance as soon as possible has become another major problem that manufacturers need to solve. However, judging from the current progress of materials science, it is difficult to fundamentally solve it in the short term.
c. The screw profile needs to be further optimized. Due to the existence of the above two problems and there is no good solution in the foreseeable future, the promotion of single-screw air compressors is limited. Therefore, scientific research institutions and large air compressor manufacturers have not invested much in the research of single-screw profiles, and have not made great progress. How to find the best screw profile is another major task before large-scale promotion. However, due to the poor market prospects, the investment of major manufacturers is not large, so it is difficult to fundamentally improve in the short term.
In general, as far as the current technological development is concerned, the twin screw air compressor is not only technologically advanced, but also fully mature in practical application.
3. Centrifugal compressor
It is the working wheel with blades rotating on the shaft of the compressor, the gas entering the working wheel is rotated by the blades, increasing the kinetic energy (speed) and static pressure head (pressure), and then the working wheel enters the diffuser, in which the speed of the gas is converted into pressure, further increasing the pressure, and the compressed gas is further compressed to the required pressure through the curve and reflow into the next stage impeller.
4. Scroll air compressor
Scroll air compressors are made up of two dynamic and static vortex disks meshing each other. In the process of suction, compression and exhaust, the static disc is fixed on the frame, and the moving disc is driven by the eccentric shaft and restricted by the anti-rotation mechanism, and rotates around the center of the base circle of the static disc for a small radius. The gas is sucked into the periphery of the static disk through the air filter element, and with the rotation of the eccentric axis, the gas is gradually compressed in several crescent-shaped compression cavities combined with the occlusion of the dynamic and static disk, and then continuously discharged from the axial hole of the central part of the static disk.
5. Sliding vane air compressor
A wheel is placed eccentrically in the compression cavity, and there are 4~6 slides on this wheel that can slide along the axis of the center of the wheel, and there is a spring at the bottom of the slide blade, which controls the slide blade to be in contact with the cavity.