Multistage compression system

A multistage compression system using refrigerant and oil, the multistage compression system comprising:

• a low-stage compressor configured to compress the refrigerant;
• a high-stage compressor configured to further compress the refrigerant compressed by the low-stage compressor;
• an oil return pipe configured to return the oil discharged by the high-stage compressor or the oil in the high-stage compressor to the low-stage compressor;
• and
• an accumulator configured to separate a liquid component of the refrigerant flowing into the low-stage compressor;
• and
• a suction pipe,
• the low-stage compressor having
• a compression part configured to compress the refrigerant, the compression part being a rotary compression part,
• a motor configured to drive the compression part, the motor being disposed above the compression part, and
• a container housing the compression part and the motor, and
• the oil return pipe being connected to a space below the motor inside the container,
• the suction pipe connecting an inside of the accumulator and the compression part, the suction pipe being provided, inside the accumulator, with an oil return hole through which the oil inside the accumulator is sent to the compression part, and
• the oil return pipe having a flow path cross-sectional area that is larger than an area of the oil return hole.

A multistage compression system using refrigerant and oil, the multistage compression system comprising:

• a low-stage compressor configured to compress the refrigerant;
• a high-stage compressor configured to further compress the refrigerant compressed by the low-stage compressor;
• an oil return pipe configured to return the oil discharged by the high-stage compressor or the oil in the high-stage compressor to the low-stage compressor;
• and
• an oil cooler in a middle of the oil return pipe,
• the low-stage compressor having
• a compression part configured to compress the refrigerant, the compression part being a rotary compression part,
• a motor configured to drive the compression part, the motor being disposed above the compression part, and
• a container housing the compression part and the motor, and
• the oil return pipe being connected to a space below the motor inside the container.

A multistage compression system using refrigerant and oil, the multistage compression system comprising:

• a low-stage compressor configured to compress the refrigerant;
• a high-stage compressor configured to further compress the refrigerant compressed by the low-stage compressor;
• an oil return pipe configured to return the oil discharged by the high-stage compressor or the oil in the high-stage compressor to the low-stage compressor;
• and
• a decompressor in a middle of the oil return pipe,
• the low-stage compressor having
• a compression part configured to compress the refrigerant, the compression part being a rotary compression part,
• a motor configured to drive the compression part, the motor being disposed above the compression part, and
• a container housing the compression part and the motor, and
• the oil return pipe being connected to a space below the motor inside the container.