A servo oil pump delivers high pressure oil to a valve unit consisting of non return valves, safety valve, pressure adjusting valve and an electrical operated proportional valve. This proportional valve, which is used to control the propeller pitch can also be manually operated.
From the proportional valve the servo oil is led to an oil distributor ring. From the oil distributor ring high pressure oil is led through pilot operated double check valves to one or the other side of the servo piston, until the desired propeller pitch has been reached.
The pilot operated double check valves keep the propeller pitch fixed in case the servo oil supply is interrupted. The propeller is equipped with an electrical pitch feed-back transducer. This feed-back signal is compared to the order signal to maintain the desired pitch. The pitch setting is normally remotely controlled, but local emergency control is possible.
Hydraulic Power Unit
Hydraulic Power Unit consists of an oil tank with all components top mounted, to facilitate installation at the yard.
Two electrically driven pumps draw oil from the oil tank through a suction filter and deliver high pressure oil to the proportional valve through a duplex full flow pressure filter. One of the 2 pumps is in service during normal operation. A sudden change of manoeuvre will start up the second pump; this second pump also serves as a stand-by pump.
A servo oil pressure adjusting valve ensures minimum servo oil pressure constantly, except during pitch changes, hereby minimizing the electrical power consumption. Maximum system pressure is set on the safety valve.
The return oil is led back to the tank through a cooler and a filter. The servo oil unit is equipped with alarms according to the Classification Society as well as necessary pressure and temperature indication.
