Abstract: An electrohydraulic steering system comprises a servo cylinder which has two chambers, an electric motor and a servo pump connected to the electric motor and being adapted to be driven in two different directions. The servo pump is directly connected to the servo cylinder and, depending on the driving direction, is able of pressurizing one or the other of the chambers of the servo cylinder with a volume flow of a hydraulic fluid. The system further comprises a control unit controlling the electric motor.

Abstract: An apparatus and process for monitoring conditions of a control valve including a valve element operated by a drive controlled by a position controller. A spindle extends into a valve chamber through a dynamic seal and connects the valve element to the drive. The condition of the seal is monitored by measuring start-up time, stopping time and distance travelled. The start-up time relates to the time between application of control current to the position controller and sensing movement of the valve element. The stopping time relates to the interval between application of a second control current to the position controller and sensing the valve element has stopped. The distance travelled relates to distance the valve clement travels during the stopping time. A time difference is determined by subtracting the stopping from the starting time and is calibrated to a seal coefficient of friction. The distance travelled is also calibrated to a seal coefficient of friction.