A method for operating a pump includes establishing a pump limit characteristics diagram by mapping a first system parameter (P1) as a function of a second system parameter (P2) to identify a permissible operating region of the pump; for each first system parameter value (P10), identifying a minimum allowable second system parameter value (P20); monitoring the first system parameter (P1) and identifying a minimum allowable second system parameter value (P20) corresponding to the monitored first system parameter value (P1m); monitoring the second system parameter (P2) and comparing the monitored second system parameter value (P2m) with the identified minimum allowable second system parameter value (P20); and regulating a control valve that controls fluid flow through a return line connecting the suction and discharge sides of the pump so that the monitored second system parameter value (P2m) does not fall below the minimum allowable second system parameter value (P20).