Abstract: Method for controlling a plural stage compressor comprising at least a first stage (10), a second stage (20) and a first inter-stage line (12) between the first stage (10) and the second stage (20), comprising the steps of: a—measuring the temperature at the inlet of the compressor, b—measuring the ratio between the outlet pressure (Pout) and the inlet pressure (Pin) of the first stage (10) of the compressor, c—calculating a coefficient (?) based at least on the value of the inlet temperature (Tin) and on the measured pressure ratio (Pout/Pin), d—if the calculated coefficient (?) is in a predetermined range, acting on a control valve (70; 76; 92) mounted in a line (4; 8) supplying the inlet of the first stage (10) of the compressor or in a gas recycle line (74) which opens into the first inter-stage line (12).

Abstract: Method for controlling a plural stage compressor comprising at least a first stage (10), a second stage (20) and a first inter-stage line (12) between the first stage (10) and the second stage (20), comprising the steps of: a—measuring the temperature at the inlet of the compressor, b—measuring the ratio between the outlet pressure (Pout) and the inlet pressure (Pin) of the first stage (10) of the compressor, c—calculating a coefficient (?) based at least on the value of the inlet temperature (Tin) and on the measured pressure ratio (Pout/Pin), d—if the calculated coefficient (?)is in a predetermined range, acting on a control valve (70; 76; 92) mounted in a line (4; 8) supplying the inlet of the first stage (10) of the compressor or in a gas recycle line (74) which opens into the first inter-stage line (12).