Patent ID: 6948335

Claim:
A compression mechanism forming a refrigerant circuit of a vapor compression refrigeration system, comprising: a refrigerant intake main pipe; n compressors with n being any integer equal to or greater than 3, which are arranged such that the second to n th compressors are connected to the refrigerant intake main pipe in sequence from an upstream side of a flow of gaseous refrigerant and the first compressor is connected downstream of the n th compressor; n oil separators with the first to n th oil separators connected to discharge sides of the respective first to n th compressors in order to separate oil from the gaseous refrigerant compressed by the first to n th compressors; and n oil return pipes arranged such that the first to n−1 oil return pipes are connected between oil outlets of the first to n−1 oil separators and intake sides of the respective second to n th compressors and the n th oil return pipe is connected between the n th oil separator and an intake side of the first compressor, the first to k oil return pipes with k being integers from 2 to n−1 are connected to the intake side of the k+1 compressor so that oil is delivered to the first compressor when the first to k compressors are running and the k+1 to n compressors are stopped.