Hydraulic lock. The wheels should be locked attheir required positions in steering mode. Forexample, the middle rear axle in heavy vehiclesshould be locked to prevent the vehicle from goinginto a snap. For this case, valve 3 is energized tomake valves 4 and 5 check the oil from the cylinders, while the valve is power-off to make valves 4and 5 open. So, valve 3 controls whether thehydraulic cylinders should be locked