The theoretical displacement of screw compressor depends on the volume between teeth, the number of teeth and the rotating speed. The volume between teeth is determined by the geometric size of the rotor. For the compressor, the possible reasons why the actual displacement is less than the theoretical displacement are:
1) leakage. There is no contact between rotors and between rotors and shells when they are running, and there is a certain gap, thus gas leakage will occur. When the gas after the pressure rises leaks to the suction pipe and the suction groove through the gap, it will reduce the displacement. In order to reduce the leakage, seal teeth are made on the top of the driven rotor, the root of the active rotor is provided with seal groove, and the end face is also processed with ring-shaped or strip-shaped seal teeth. If these sealing lines are worn, the leakage volume will increase and the exhaust volume will decrease;
2) inhaling state. Screw compressor is a volume compressor with constant suction volume. When the suction temperature rises, or the suction pressure decreases due to the excessive resistance of the suction pipeline, the density of the gas decreases, which accordingly reduces the mass displacement of the gas;
3) cooling effect. During the process of gas compression, the temperature will rise, and the temperature of rotor and chassis will also rise accordingly. Therefore, during the process of suction, the gas will expand due to the heating of rotor and chassis, therefore, the suction volume will be reduced accordingly. Some of the rotors of screw-type air compressor adopt oil cooling, while the chassis is cooled by water, one of the purposes of which is to lower its temperature. When the cooling effect is not good, the temperature will rise and the displacement will decrease;
4) rotating speed. The displacement of screw compressor is proportional to the rotating speed. And the rotating speed often changes with the voltage and frequency of the power grid. When the voltage decreases (for asynchronous motor) or the frequency decreases, the rotating speed will decrease and the gas volume will decrease.
