What is the reason why the actual exhaust volume of the screw air compressor is less than the theoretical exhaust?

Author : RUNNINGWAY

Update time : 2021-11-18 16:21:39

What is the reason why the actual exhaust volume of the screw air compressor is less than the theoretical exhaust? Theoretically speaking, the displacement of a screw air compressor depends on the volume between the teeth, the number of teeth and the speed. The volume between teeth is determined by the geometry of the rotor.

In practice, for screw air compressors, there are four possible reasons why the actual displacement is less than the theoretical displacement:

1) Leakage. There is no contact between the rotors and between the rotor and the housing during operation, and a certain gap is maintained, so gas leakage will occur. When the pressure increased gas leaks through the gap to the suction pipe and the sucking groove, the exhaust volume will be reduced. In order to reduce the amount of leakage, sealing teeth are made on the tooth top of the driven rotor, sealing grooves are opened on the tooth root of the driving rotor, and ring-shaped or strip-shaped sealing teeth are also machined on the end surface. If these sealing lines are worn, the leakage will increase and the exhaust will decrease;

2) Inhalation state. The screw air compressor is a positive displacement compressor with the same suction volume. When the suction temperature rises or the suction pressure decreases due to the excessive resistance of the suction pipe, the density of the gas will decrease, which will correspondingly reduce the mass and exhaust volume of the gas;

3) Cooling effect. The temperature of the gas will rise during the compression process, and the temperature of the rotor and the casing will also rise accordingly. Therefore, during the suction process, the gas will be heated by the rotor and the casing and expand, so the suction volume will be reduced accordingly. Some of the rotors of screw air compressors are cooled by oil, and the casing is cooled by water. One of the purposes is to reduce its temperature. When the cooling effect is not good, the temperature will increase and the exhaust volume will decrease;

4) Rotation speed. The displacement of the screw compressor is proportional to the speed. The speed often changes with the voltage and frequency of the grid. When the voltage is reduced (for asynchronous motors) or the frequency is reduced, the speed will drop and the air volume will be reduced.

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