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The Basic Working Principle and Knowledge of Twin Screw Air Compressor

December 28, 2021

The screw air compressor is a positive displacement compressor, which achieves the purpose of gas compression through the gradual reduction of the working volume.

The working volume of the screw air compressor is composed of a pair of tooth grooves of the rotors which are placed parallel to each other and meshed with each other and a casing containing the pair of rotors. When the machine is running, the teeth of the two rotors are inserted into each other's slots, and as the rotor rotates, the teeth inserted into the other's slots move to the exhaust end, so that the volume enclosed by the other teeth is gradually reduced, and the pressure is gradually increased until it reaches the required value. When the pressure is required, the cogging side is connected to the exhaust port to achieve exhaust.

After a tooth groove is inserted by a tooth that is engaged with it, two spaces separated by the tooth are formed. The tooth groove near the suction end is the suction volume, and the one close to the discharge end is the volume of compressed gas. With the operation of the compressor, the teeth of the opposite rotor inserted into the tooth slots move to the exhaust end, so that the suction volume is continuously expanded, and the volume of compressed gas is continuously reduced, thereby realizing the suction compression process in each tooth slot. When the gas pressure of the compressed gas in the tooth groove reaches the required exhaust pressure, the tooth groove is just in communication with the exhaust port, and the exhaust process is started. The change of the suction volume and the compression volume divided by the tooth grooves of the opposite rotor is repeated, so that the compressor can continuously suck in, compress and discharge.


The working principle and structure of screw compressor:

1. Inhalation process:

The screw-type intake side air intake port must be tapped.) When the pi group soils, the tooth groove space of the main and auxiliary rotors is transferred to the intake end wall valve group, and the air intake only depends on the opening of a regulating valve. Later, the sky d sounds T, and the Japanese Rong Ding right is open to the public, because when the air in the tooth groove is fully opened during exhaust, the space z* is large. The boundary air is sucked in, flows into the main axis along the axis and is discharged. When the exhaust is finished, the tooth groove is in a vacuum state. When it reaches the mouth, the molecule → the side end face of the letter is turned away from the tooth groove of the auxiliary rotor of the casing. Inside. Screw air compressor maintenance reminds that when the air fills the entire tooth groove, the end of the inlet side of the rotor turns away from the casing.

The air inlet, the air between the tooth grooves is closed.

2. Sealing and conveying process:

When the suction of the main and auxiliary rotors ends, the peaks of the main and auxiliary rotors are sealed with the casing. At this time, the air is closed in the grooves and no longer flows out, that is, [closed process]. The two rotors continue to rotate, and their tooth peaks and grooves coincide at the suction end, and the anastomotic surface gradually moves to the exhaust end.

3. Compression and fuel injection process:

During the conveying process, the meshing surface gradually moves to the exhaust end, that is, the tooth groove between the meshing surface and the exhaust port gradually decreases, the gas in the tooth groove is gradually compressed, and the pressure increases, which is the [compression process]. At the same time of compression, the lubricating oil is sprayed into the compression chamber and mixed with the chamber air due to the effect of the pressure difference.

4. Exhaust process:

When the meshing end surface of the rotor of the screw air compressor is turned to communicate with the exhaust of the casing, (the pressure of the compressed gas is high at this time) the compressed gas starts to be discharged until the meshing surface of the tooth peak and the tooth groove moves to Exhaust end surface. At this time, the tooth groove space between the meshing surface of the two rotors and the exhaust port of the casing is zero, and the (exhaust process) is completed. At the same time, the length of the tooth groove between the meshing surface of the rotor and the intake port of the casing is again When the z* length is reached, the inhalation process is proceeding again.

Screw compressors are divided into: open type, semi-closed type, and fully enclosed type

1. Fully enclosed screw compressor:

The body adopts a high-quality, low-porosity cast iron structure with small thermal deformation; the body adopts a double-walled structure with an exhaust channel inside, which has high strength and good noise reduction effect; the body and outside forces are basically balanced, no open type, semi-closed Withstand the risk of high pressure; the shell is made of steel, with high strength, beautiful appearance and light weight. With vertical structure, the compressor occupies a small area, which is conducive to the arrangement of multiple heads of the chiller; the lower bearing is immersed in the oil tank, and the bearing is lubricated; the axial force of the rotor is reduced by 50% compared with the semi-closed and open type (motor shaft on the exhaust side) The balance function); There is no risk of the horizontal motor cantilever, and the reliability is high; it avoids the influence of the screw rotor, the slide valve, and the motor rotor on the matching accuracy, and improves the reliability; the assembly process is good. The vertical screw design of the oil-free pump prevents oil shortage when the compressor is running or shutting down. The lower bearing is immersed in the oil tank as a whole, and the upper bearing uses differential pressure to supply oil; the system has low pressure differential requirements. In emergency situations, the bearing lubrication protection function can prevent the bearing from lacking lubrication, which is beneficial to the opening of the unit during the transition season.

Disadvantages: exhaust cooling is used, and the motor is at the exhaust port, which will easily cause the motor coil to burn out; in addition, failures cannot be eliminated in time.

2. Semi-hermetic screw compressor

The motor is cooled by spray liquid, and the motor has a low operating temperature and long life; the open compressor uses air to cool the motor, and the motor has a higher operating temperature, which affects the life of the motor, and the working environment of the machine room is poor; if the exhaust gas is used to cool the motor, the motor has a high operating temperature. The motor life is short. Generally, the external oil separator has a large volume, but the efficiency is very high; the built-in oil separator is combined with the compressor, and the volume is small, so the effect is relatively poor. The secondary oil separation effect can reach 99.999%, which can ensure good lubrication of the compressor under various working conditions.

However, the plunger type semi-hermetic screw compressor is geared to increase the speed, the speed is high (about 12000 rpm), the wear is large, and the reliability is poor.

3. Open type screw compressor

The advantages of the open-type unit are:

1) The compressor is separated from the motor, so that the compressor has a wider range of applications;

2) The same compressor can be used with different refrigerants. In addition to using halogenated vertical refrigerants, ammonia can also be used as a refrigerant by changing the materials of some parts;

3) Motors of different capacities can be equipped according to different refrigerants and operating conditions.

The main disadvantages of open-type units are:

(1) The shaft seal is easy to leak, which is also the object of frequent maintenance by users;

(2) The equipped motor rotates at a high speed, the airflow noise is large, and the compressor itself is also noisy, which affects the environment;

(3) It is necessary to configure complicated oil system components such as separate oil separator and oil cooler. The unit is bulky and inconvenient to use and maintain.

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