Positive displacement expander and refrigeration cycle apparatus including positive displacement expander

A positive displacement expander that generates power using fluid energy generated while a high-pressure fluid, supplied to a plurality of expansion chambers partitioned by an orbiting scroll, is being expanded and decompressed, the positive displacement expander comprising:

• an expander discharge space to which the fluid expanded at the expansion chambers discharges;
• a discharge pipe that discharges the fluid from the expander discharge space;
• a communicating pipe that allows each of the expansion chambers to communicate with the discharge pipe;
• a solenoid valve disposed in the communicating pipe, and
• a controller operatively connected to said solenoid valve and controlling said solenoid valve, said controller configured to open the solenoid valve, in a time period after the supply of the high-pressure fluid to the expansion chambers has stopped and prior to a time when the pressures of each of the expansion chambers and the discharge pipe would be equalized, and the controller opening said solenoid valve within said time period so as to equalize the pressure between each of the expansion chambers and the discharge pipe in such a way that the orbiting scroll is stopped at a predetermined position.