The steering control unit is a rotary valve that controls the movement of the steering cylinder. The supply of oil for the unit comes from the steering hydraulic pump. The control unit has a minimum restriction to oil flow when the steering wheel is not moved. The control unit has four ports. A manifold block is installed on the steering control unit over the four ports. The inlet port in the manifold block has a check valve (steering control valve) and a relief valve and is connected to the hydraulic pump. The relief valve is set at 11.7 to 12.4 MPa (1700 to 1800 psi). Two of the ports are connected to the steering cylinder. The port for the drain circuit is connected to the inlet of the brake valve. All of the oil that flows to the steering control unit flows to the brake valve.