
{"publication_number": "US-8939704-B2", "abstract": "a method for operating a multistage compressor is provided . the method includes monitoring the pump limit , wherein at least a first measurement parameter measured during operation is compared to a reference parameter . the reference parameter is characteristic of reaching the surge limit or a specific distance of the operating point from the surge limit . a multistage compressor is also provided . in order to enlarge the operating range without risking safety , it is proposed that each stage to be monitored individually for the onset of the surge .", "application_number": "US-200913130619-A", "description": "fig2 shows a diagrammatic illustration of the method according to the invention , applied to a compressor co with four stages st 1 , st 2 , st 3 , st 4 . the designations of fig1 are to be applied to fig2 to denote the same elements ( substantially the compressor line which is the subject matter of the invention ). at the first stage st 1 and the third stage st 3 , the compressor co in each case has an adjustable inlet guide vane apparatus igv 1 , igv 3 . an intercooler ic 1 to ic 4 ( the intercooler ic 4 of the last stage st 4 is actually an aftercooler , but this distinction is not made in the sequence for reasons of simplification ) is provided in each case between the stages st 1 to st 4 and after the last stage st 4 . the compressor co delivers a process fluid pf , the volumetric flow { dot over ( v )