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Capacity control in screw compressors
Capacity screw compressor is controlled by varying the degree of opening of the valves are located in the housing tags rotors. This valve is closed (100% power), only a couple of entering the machine is compressed and discharged in capacitor. With the valve is fully open (minimum capacity) about 90% of couples allowed to flow directly to the suction uncompressed. Due to the internal losses of the screw compressor (proportionally more than the rate of capacity) with partial load operation below 60% is relatively inefficient. Figure 15 shows the change of power over the power range of a typical screw with an operating ratio to condensation evaporating pressure 4:1.
Variable speed drive is now available as a method of controlling the power screw compressor allows to improve efficiency at part load.
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