Patent ID: 7665973

Claim:
An apparatus for changing capacity of a multi-stage compressor, comprising: a first cylinder provided with a first suction port and a first discharge port, wherein the first cylinder has a first inner space formed therein that is divided into a first suction chamber and a first compression chamber by a first rolling piston that orbits therein and a first vane that moves linearly so as to maintain contact with the first rolling piston; a second cylinder provided with a second suction port and a second discharge port, wherein the second cylinder has a second inner space formed therein that is divided into a second suction chamber and a second compression chamber by a second rolling piston that orbits therein and a second vane that moves linearly so as to maintain contact with the second rolling piston; a middle bearing positioned between the first cylinder and the second cylinder, the middle bearing having a valve hole formed therein and a bypass hole that intersects the valve hole so as to allow communication between the first and second compression chambers; a sliding valve slidably coupled to the valve hole so as to selectively open or close the bypass hole, wherein the sliding valve comprises a hollow cylindrical body having a closed end and an open end; a pressure switching unit that selectively supplies discharge pressure to one end of the sliding valve; a valve stopper provided at an outer end portion of the valve hole, wherein the valve stopper contacts the open end of the sliding valve so as to restrict movement of the sliding valve during an opening operation; an elastic member interposed between the sliding valve and the valve stopper; a stopping protrusion that extends outward from the open end of the sliding valve; and a valve stopping projection formed at an inner circumferential surface of the valve hole, wherein the valve stopping projection contacts the stopping protrusion so as to restrict movement of the sliding valve during a closing operation of the sliding valve, wherein the elastic member is fixed at spring fixing steps respectively formed on inner circumferential surfaces of the sliding valve and the valve stopper, and wherein the elastic member draws the sliding valve toward the valve stopper when pressure at a cylinder side of the sliding valve and a back pressure are balanced so as to open the bypass hole, wherein the elastic member is positioned outside of the flow path of the bypass hole so as to allow refrigerant to flow without resistance.