OIL SYSTEM D/O (3)OIL SYSTEM OPERATIONThe operation of the oil system is divided into three parts:- storage,- pressure flow,- scavenge flow and vent.PRESSURE FLOWThe oil is drawn from the oil tank through a strainer by suction fromthe pressure pump as the gearbox starts to turn. The pump assemblyalso includes a cold-start relief valve, which protects the system byrelieving excessive pressure back to the pump inlet. The pressurepump increases the pressure and supplies oil through the pressurefilter to the Air Oil Heat Exchanger (AOHE).The AOHE is made up of a heat exchanger and an air modulatingvalve. In certain operating conditions, the AOHE uses LP air todecrease the oil temperature. From the AOHE, oil flows to the FuelOil heat Exchanger (FOHE). The FOHE has two functions. Theprimary function is to decrease the oil temperature and the secondaryfunction is to increase the temperature of the fuel to prevent icing.Both heat exchangers have cold start relief valves, which will bypassthe exchangers when the oil pressure is excessive.For lubrication and cooling purposes, the oil flows from the FOHEto the different users:- front bearing chamber,- LP/Intermediate Pressure (IP)/High Pressure (HP) location bearingchamber and internal gearbox,- HP/IP turbine bearing chamber,- LP turbine bearing chamber,- intermediate gearbox assembly,- gearbox input drive,- external gearbox and centrifugal breather.