A hydraulic circuit on a harvesting machine for controlling the movement of a knife sharpening arrangement. The circuit comprises a pressure source, a pressure sink, a multi port valve, a first hydraulic cylinder which moves a knife sharpening device and a second hydraulic cylinder which moves a flap of a housing in which the knife sharpening device is housed. Each cylinder is connected to a respective valve arrangement and each respective valve arrangement will conduct fluid when a predetermined fluid pressure is reached. Movement of the multiport valve moves the first or second hydraulic cylinder so that when one of said first or second cylinders reaches a maximum deflection, the pressure in said circuit is greater than the predetermined fluid pressure of the respective valve arrangement of the other of said first or second cylinders so that said other first or second cylinder moves.
