Capacity control device and capacity control method for screw compressor

Abstract

An object of the invention is to provide a capacity control device of a screw compressor capable of restraining the consumption of components such as a suction throttle valve and of extending the life of the components. According to the present invention, there is provided a capacity control device of a screw compressor which controls a suction throttle valve by a controlled pressure at which a load operation state is switched to a low pressure operation, and by a minimum operation pressure at which the low pressure operation is switched to the load operation, the capacity control device being characterized by comprising: a pressure detector 15 which detects a discharge pressure of the compressor 1; and a control device 16 which calculates a cycle time between the load operation and the low pressure operation on the basis of the measured pressure detected by the pressure detector 15, and which changes the controlled pressure to a high pressure side when the cycle time becomes not longer than a shortest period specified beforehand on the basis of the life of each component.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a schematic diagram showing a whole configuration of an embodiment of an oil cooled screw compressor and a capacity control device of the oil cooled screw compressor according to the present invention;

FIG. 2 is a characteristic diagram showing compressor pressure fluctuation caused in the embodiment of the capacity control device of the oil cooled screw compressor according to the present invention shown in FIG. 1;

FIG. 3 is a flowchart diagram for control performed in the embodiment of the capacity control device of the oil cooled screw compressor according to the present invention shown in FIG. 1;

FIG. 4 is a characteristic diagram showing compressor pressure fluctuation caused in another embodiment of a capacity control device of an oil cooled screw compressor according to the present invention; and

FIG. 5 is a figure showing a comparison of energy-saving characteristics between another embodiment of the capacity control device of the oil cooled screw compressor according to the present invention and the other capacity control methods.

Claims

1. A capacity control device of a screw compressor which controls a suction throttle valve by a controlled pressure at which a load operation state is switched to a low pressure operation, and by a minimum operation pressure at which the low pressure operation is switched to the load operation, the capacity control device comprising: a pressure detector which detects a discharge pressure of the compressor; and a control device which calculates a cycle time between the load operation and the low pressure operation on the basis of the measured pressure detected by the pressure detector, and which changes the controlled pressure to a high pressure side when the cycle time becomes not longer than a shortest period specified beforehand on the basis of the life of each component.

2. A capacity control device of an oil cooled screw compressor which controls a suction throttle valve by a controlled pressure at which a load operation state is switched to a low pressure operation, and by a minimum operation pressure at which the low pressure operation is switched to the load operation, the capacity control device comprising: a pressure detector which detects a discharge pressure of the compressor; and a control device which calculates a cycle time between the load operation and the low pressure operation on the basis of the measured pressure detected by the pressure detector, which changes the controlled pressure to a high pressure side when the cycle time becomes not longer than a shortest period specified beforehand on the basis of the life of each component, and which effects a shift to suction throttle control when the cycle time cannot be prevented from becoming not longer than the shortest period by the increase of the controlled pressure.

3. The capacity control device of the screw compressor according to claim 1, wherein the shortest period is specified on the basis of the life of the suction throttle valve.

4. The capacity control device of the screw compressor according to claim 2, wherein the shortest period is specified on the basis of the life of the suction throttle valve.

5. A capacity control method of a screw compressor which controls a suction throttle valve by a controlled pressure at which a load operation state is switched to a low pressure operation, and by a minimum operation pressure at which the low pressure operation is switched to the load operation, the capacity control method comprising: calculating a cycle time between the load operation and the low pressure operation by a control device on the basis of a measured pressure detected by a pressure detector which detects a discharge pressure of the compressor; and changing the controlled pressure to a high pressure side when the cycle time becomes not longer than a shortest period specified beforehand on the basis of the life of each component.

6. A capacity control method of an oil cooled screw compressor which controls a suction throttle valve by a controlled pressure at which a load operation state is switched to a low pressure operation, and by a minimum operation pressure at which the low pressure operation is switched to the load operation, the capacity control method comprising: calculating a cycle time between the load operation and the low pressure operation by a control device on the basis of a measured pressure detected by a pressure detector which detects a discharge pressure of the compressor; changing the controlled pressure to a high pressure side when the cycle time becomes not longer than a shortest period specified beforehand on the basis of the life of each component; and effecting a shift to suction throttle control when the cycle time cannot be prevented from becoming not longer than the shortest period by the increase of the controlled pressure.