Patent ID: 8182680

Claim:
A pump unit comprising: a primary piston pump with a primary piston and a secondary piston pump with a secondary piston, the primary piston pump being fluidically connected with the secondary piston pump, the pump unit operating periodically according to a pump cycle comprising a compression stroke of the primary piston and a subsequent deliver-and-fill phase for delivering fluid from the primary piston pump to the secondary piston pump and to a fluidic system located downstream of the pump unit; a pressure detection unit configured for determining a fluid pressure of fluid dispensed by the pump unit at an outlet of the secondary piston pump; and a control unit configured for switching closed loop control between controlling a position of the secondary piston in dependence on the fluid pressure determined by the pressure detection unit during the compression stroke, while a predefined position-versus-time curve is performed by the primary piston, and controlling a position of the primary piston in dependence on the fluid pressure determined by the pressure detection unit during the deliver-and-fill phase, while a predefined position-versus-time curve is performed by the second piston.