A method includes driving a fluid pumping unit having a plurality of pumping cylinders via a plurality of hydraulic cylinders respectively of a hydraulic power unit. The method further includes controlling activation of the hydraulic power unit such that each stroke of the corresponding piston assembly between the top dead center and the bottom dead center follows a corresponding trapezoidal velocity profile with respect to a time duration. Controlling activation includes controlling flow of a hydraulic fluid in the hydraulic power unit so as to control the corresponding trapezoidal velocity profile with respect to the time duration of the corresponding piston assembly to obtain a predefined flow rate of the fluid medium from the pumping unit.