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.

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.