Abstract: Agricultural implement to be conveyed by a self propelled vehicle includes a structural frame and a substructure moveable between a raised position and a lowered position. The substructure has at least one ground engaging tool supported thereon so as to engage the ground when the substructure is moved to the lowered position. A fluid circuit is provided to control engagement of the tool with the ground. The fluid circuit includes a first check valve having a first side connectable to a source of pressurized fluid flow and a second side connected to a fluid cylinder. The fluid cylinder is operated between a retracted position and an extended position to move the substructure between the raised position and the lowered position, respectively. A second check valve is provided having a first side connected to drain and a second side connected to the fluid cylinder. A sensor assembly opens the second check valve when pressurized fluid flow is received by the first side of the first check valve.