COMPONENT OPERATION / Steering Valve

Overload Relief Valve

The overload relief valves are located in the steering valve and prevent the circuit pressure between the steering cylinder and the steering valve from increasing beyond the set pressure.

When an external force is applied to the left and right steering directions, surge oil pressure is developed in the circuit. When the circuit pressure exceeds the set spring force of the overload relief valve, the poppet in the overload relief valve moves to the right and the oil passage is opened so that pressure oil flows to the hydraulic oil tank.

When the circuit pressure decreases, the poppet moves to the left due to the spring force so that the oil passage is closed again.

MAKE-UP VALVE

The make-up valves are located in the steering valve. When the circuit pressure between the steering cylinder and the steering valve is lower than the pressure in hydraulic oil tank, the make-up valve draws the hydraulic oil from port T in order to prevent the cavitation.

When the circuit pressure between the steering cylinder and the steering valve is lower than the pressure in the hydraulic oil tank, the ball of the make-up valve moves to the right and the oil passage is opened. Therefore, hydraulic oil from port T is drawn and delivered to the circuit between the steering cylinder and the steering valve.

When the circuit pressure between the steering cylinder and the steering valve increases, the ball is moved to the left by pressure oil and the oil passage is closed again.

T3-3-6

COMPONENT OPERATION / Steering Valve