Hydraulic steering systems are now being used in every category of small vessel. In many respects hydraulic steering is preferable to mechanical steering. Hydraulic systems normally comprise of two main components, a steering wheel pump and steering cylinder(s). The steering wheel pump may be either a gear pump or a plunger pump. Which ever type is installed, steering is achieved by turning the steering wheel in either direction causing oil from the wheel pump to be supplied to the appropriate side of the cylinder. Oil is returned via the opposite side of the cylinder back to the pump.
The linear motion of the cylinder rod is transformed to a rotary motion by the tiller, which turns the rudder shaft and rudder. Check valves (non-return valves) are usually incorporated to prevent the rudder driving the steering wheel pump. If an autopilot is to be included in such a hydraulic steering system, then the oil flow providing the rudder movement must be controlled by electrical signals from the autopilot. The maximum flow rate of RPU80, RPU160 and RPU300 is 0,8 l/min., 1,6 l/min. and 3,0 l/min. respectively, measured at a pressure of 10 bar with nominal voltage (12 VDC) on the motor terminals.