SCROLL COMPRESSOR AND ITS BACK PRESSURE CHAMBER PRESSURE CONTROL VALVE

PROBLEM TO BE SOLVED: To control pressure in a back pressure chamber minutely with a simple structure and with a good efficiency by providing with a pressure control means for controlling intermediate pressure for push-pressing a scroll toward the other scroll and applied in the back pressure chamber, to a target value which is decided by a function of a pressure ratio between intake pressure and discharge pressure. SOLUTION: In a back pressure chamber pressure control system, intermediate pressure between discharge pressure detected by a discharge pressure detecting means 111 and intake pressure detected by an intake pressure detecting means 112, is supplied to a back pressure chamber 82 through a back pressure control valve 100 which communicates with discharge piping 101 and intake piping 102, and non-turning scroll 51 which is floating supported is pushed toward a turning scroll 61. A target value of intermediate pressure applied on the back pressure chamber 82 is calculated by a controller 110 as the function of a pressure ratio between discharge pressure and intake pressure, it is detected by a back pressure chamber detecting means 113 whether real pressure in the back pressure chamber 82 attains a target value or not, and intermediate pressure is controlled by a controller 110 so as to match with the target value.