This paper investigates a concept for the pure hydraulic control of a buck converter using a hydraulically piloted 2-2 way on-off valve. The pilot system is controlled by the desired output pressure of the buck converter in form of a pressure signal and the RC filtered feedback of the actual pressure. These pressures act via small plunger cylinders in opposite direction on the on-off valve. An additional pilot cylinder features a jumping active hydraulic area for a robust feedback. The valve performs close to rectangular oscillations, the frequency of which is mainly determined by the characteristic time of the RC filter. The concept is studied by a simple analytical model to obtain its basic operating characteristics and by a detailed numerical model to analyze the role of parasitic effects on system performance. The paper shows that this concept works and can robustly follow the commanded output pressure. The converter has a moderate response dynamics; in certain operation conditions it shows an aperiodic behavior by alternating between phases of periodic switching and pause.

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