Two-stage compression refrigeration cycle

1. A two-stage pressurizing refrigeration cycle, comprising:

a low-stage side compressor that compresses and discharges a refrigerant in which a lubricating oil is mixed;

a high-stage side compressor that compresses and discharges the refrigerant discharged from the low-stage side compressor;

a low-stage side suction pipe connected to a refrigerant suction side of the low-stage side compressor;

a low-stage side discharge pipe that connects a refrigerant discharge side of the low-stage side compressor to a refrigerant suction side of the high-stage side compressor;

a high-stage side discharge pipe connected to the refrigerant discharge side of the high-stage side compressor;

a bypass pipe branched from the low-stage side suction pipe and connected to the low-stage side discharge pipe, the bypass pipe being configured to guide the refrigerant to the high-stage side compressor while bypassing the low-stage side compressor when the low-stage side compressor stops; and

a check valve provided in the bypass pipe, the check valve being configured to allow a flow of the refrigerant from the low-stage side suction pipe to the low-stage side discharge pipe, while blocking a flow of the refrigerant from the low-stage side discharge pipe to the low-stage side suction pipe, wherein

a suction-side guiding portion is provided in a part of the low-stage side suction pipe that leads from a bypass branch portion, at which the bypass pipe is branched, to the refrigerant suction side of the low-stage side compressor, the suction-side guiding portion being configured to guide the lubricating oil from the refrigerant suction side of the low-stage side compressor to a side of the bypass branch portion, and

the suction-side guiding portion is located at a position in a vertical direction that is equal to or higher than a position in the vertical direction of the bypass branch portion, and a part of the suction-side guiding portion on the refrigerant suction side of the low-stage side compressor is located at a higher position in the vertical direction than a part of the suction-side guiding portion on the side of the bypass branch portion.

2. The two-stage pressurizing refrigeration cycle according to claim 1 , wherein

the low-stage side compressor is disposed at a higher position in the vertical direction than the bypass branch portion.

3. The two-stage pressurizing refrigeration cycle according to claim 1 , wherein

the bypass pipe is provided with a bypass-side guiding portion that guides the lubricating oil from a side of the check valve to the side of the bypass branch portion, and

the bypass-side guiding portion is located at a position in the vertical direction that is equal to or higher than a position in the vertical direction of the bypass branch portion, while a part of the bypass-side guiding portion on the side of the check valve is located at a higher position in the vertical direction than a part of the bypass-side guiding portion on the side of the bypass branch portion.

4. The two-stage pressurizing refrigeration cycle according to claim 3 , wherein

the check valve is disposed at a higher position in the vertical direction than the bypass branch portion.

5. The two-stage pressurizing refrigeration cycle according to claim 1 , wherein

the high-stage side discharge pipe is provided with an oil separator to separate the lubricating oil from the refrigerant containing the mixed lubricating oil, and is connected to an oil return pipe that guides the lubricating oil separated by the oil separator to the low-stage side suction pipe, and

the oil return pipe is connected to the low-stage side suction pipe at a connection portion that is positioned in the low-stage side suction pipe from the bypass branch portion to the refrigerant suction side of the low-stage side compressor.

6. The two-stage pressurizing refrigeration cycle according to claim 1 , wherein

the high-stage side discharge pipe is provided with an oil separator to separate the lubricating oil from the refrigerant containing the mixed lubricating oil, and is connected to an oil return pipe to guide the lubricating oil separated by the oil separator to the bypass pipe, and

the oil return pipe is connected to the bypass pipe at a connection portion that is positioned in the bypass pipe from the bypass branch portion to the check valve.

7. A two-stage pressurizing refrigeration cycle, comprising:

a low-stage side compressor that compresses and discharges a refrigerant in which a lubricating oil is mixed;

a high-stage side compressor that compresses and discharges the refrigerant discharged from the low-stage side compressor;

a low-stage side suction pipe connected to a refrigerant suction side of the low-stage side compressor;

a low-stage side discharge pipe that connects a refrigerant discharge side of the low-stage side compressor to a refrigerant suction side of the high-stage side compressor;

a high-stage side discharge pipe connected to the refrigerant discharge side of the high-stage side compressor;

a bypass pipe branched from the low-stage side suction pipe and connected to the low-stage side discharge pipe, the bypass pipe being configured to guide the refrigerant to the high-stage side compressor while bypassing the low-stage side compressor when the low-stage side compressor stops; and

a check valve provided in the bypass pipe, the check valve being configured to allow a flow of the refrigerant from the low-stage side suction pipe to the low-stage side discharge pipe, while blocking a flow of the refrigerant from the low-stage side discharge pipe to the low-stage side suction pipe, wherein

the low-stage side suction pipe is provided with a bypass branch portion at which the bypass pipe is branched from the low-stage side suction pipe,

the bypass pipe is provided with a bypass-side guiding portion to guide the lubricating oil from a side of the check valve to a side of the bypass branch portion,

the bypass-side guiding portion is located at a position in a vertical direction that is equal to or higher than a position in the vertical direction of the bypass branch portion, and a part of the bypass-side guiding portion on the side of the check valve is located at a higher position in the vertical direction than a part of the bypass-side guiding portion on the side of the bypass branch portion,

the high-stage side discharge pipe is provided with an oil separator to separate the lubricating oil from the refrigerant containing the mixed lubricating oil, and is connected to an oil return pipe that guides the lubricating oil separated by the oil separator to the low-stage side suction pipe, and

the oil return pipe is connected to the low-stage side suction pipe at a connection portion that is positioned in the low-stage side suction pipe from the bypass branch portion to the refrigerant suction side of the low-stage side compressor.

8. A two-stage pressurizing refrigeration cycle, comprising:

a low-stage side compressor that compresses and discharges a refrigerant in which a lubricating oil is mixed;

a high-stage side compressor that compresses and discharges the refrigerant discharged from the low-stage side compressor;

a low-stage side suction pipe connected to a refrigerant suction side of the low-stage side compressor;

a low-stage side discharge pipe that connects a refrigerant discharge side of the low-stage side compressor to a refrigerant suction side of the high-stage side compressor;

a high-stage side discharge pipe connected to the refrigerant discharge side of the high-stage side compressor;

a bypass pipe branched from the low-stage side suction pipe and connected to the low-stage side discharge pipe, the bypass pipe being configured to guide the refrigerant to the high-stage side compressor while bypassing the low-stage side compressor when the low-stage side compressor stops; and

a check valve provided in the bypass pipe, the check valve being configured to allow a flow of the refrigerant from the low-stage side suction pipe to the low-stage side discharge pipe, while blocking a flow of the refrigerant from the low-stage side discharge pipe to the low-stage side suction pipe, wherein

the low-stage side suction pipe is provided with a bypass branch portion at which the bypass pipe is branched from the low-stage side suction pipe,

the bypass pipe is provided with a bypass-side guiding portion to guide the lubricating oil from a side of the check valve to a side of the bypass branch portion,

the bypass-side guiding portion is located at a position in a vertical direction that is equal to or higher than a position in the vertical direction of the bypass branch portion, and a part of the bypass-side guiding portion on the side of the check valve is located at a higher position in the vertical direction than a part of the bypass-side guiding portion on the side of the bypass branch portion,

the high-stage side discharge pipe is provided with an oil separator to separate the lubricating oil from the refrigerant containing the mixed lubricating oil, and is connected to an oil return pipe to guide the lubricating oil separated by the oil separator to the bypass pipe, and

the oil return pipe is connected to the bypass pipe at a connection portion that is positioned in the bypass pipe from the bypass branch portion to the check valve.