Servo steering. In Figure 2, the servo solenoidvalve 1 is the key component to control thesteering system, and its characteristics determinethe system dynamic performance. When steering, directional valve 3 is in the normal positionto allow pilot check valves 4 and 5 bidirectionaloperation, and valve 2 is also in the normalposition. Relief valves 6 and 7 are safety valves.Valve 1 could be a proportional, servo solenoid,or servo valve. We have discussed the choice ofvalve type below. Valve 1 is adjusted by aclosed-loop control system according to thesteering error between command and actualangles, measured by the angle sensor. Thus, thesteering wheels can be controlled accurately bythe system