The device for energy-optimization on operation of several centrifugal pumps controlled in rotational speed, in a hydraulic installation, begins firstly with determining which pumps as pilot pumps are assigned directly to a consumer and which pumps are hydraulically connected in series upstream of the pilot pumps. Thereafter, one or more energy-optimization circuits are formed, which in each case consist of one or more pilot pumps and of one or more pumps connected in series upstream, which deliver into the pilot pumps, wherein the energy-optimization circuits are selected such that the pumps connected in series upstream in each case are assigned to only one energy-optimization circuit, whereupon the energy-optimization circuits are energy-optimized with respect to the pumps.