Abstract: An operating and down-pressure hydraulic control system for vehicle-mounted implements such as earth compactors and the like. The assembly of hydraulic cylinders, valving and a hydraulic accumulator provided herein operates as a hydraulic system to raise, lower and otherwise position an implement and to provide down-pressure to it. The assembly also permits the hydraulic support of the implement to flex, while maintaining down-pressure on it, when the ground surface elevation rises or falls away relative to the implement as it moves over the ground being worked.