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the Accessory Cooling System (Ref. 49-52-00),
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the APU Control and Monitoring System (Ref. 49-61-00),
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the Oil Indicating System (Ref. 49-93-00),
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the Low Oil Pressure and the High Oil Temperature Warning System (Ref. 49-94-00).
5. Component Description
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A. Oil Pump
The lube module consists of:
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a high-pressure pump,
-
a scavenge pump for the turbine bearing,
-
a scavenge pump for the generator,
- oil filters,
-differential pressure switches,
-a high-pressure relief valve and regulator.
(1)
This lube module is installed onto the gearbox. The housing has a flange for installation of the fuel control unit. The steel shaft of the pump is spline driven from the gearbox and runs on bronze bushes that are force-lubricated with oil.
(2)
The oil pressure regulation-valve is of the spool and sleeve type. It is installed in the lube module and controls the oil pressure
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B. Oil Filters The main components of the oil filter are:
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the filter housings,
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the filter elements,
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the differential pressure switches,
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the differential pressure bypass valves. Two micronic oil filters are installed in the APU oil system, one for high-pressure supply and one for the generator oil scavenge. The 25 micron absolute disposable filter elements are made of corrugated fiberglass and are installed inside housings. The two filter housings have a differential pressure switch that transmit a signal to the CFDS when the filter is clogged. When this occurs, it is necessary to change the filter. A differential pressure between the inlet and the outlet of the filter of 30 psi (2.0684 bar) to 40 psi (2.7579 bar) causes the switch to transmit a signal to the CFDS. The differential-pressure bypass valve opens when the pressure increases to more than 55 psi (3.7921 bar) for the lube filter and 100 psi (6.8947 bar) for the generator scavange filter.
C. Oil Cooler The main components of the oil cooler are:
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the oil cooler housing,
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the thermal bypass valve. The oil cooler is a plate type air-oil heat exchanger. The oil flows through hollow plates that are installed inside a housing. A cooling fan blows air across the plates to an outlet. This removes the heat that has been transferred from the oil to the plates. A thermal bypass valve is installed at the oil cooler inlet and is extanded at oil temperatures above 77 deg.C (170.60 deg.F). The valve begins to close at an oil temperature of 60 deg.C (140.00 deg.F) and the oil flows through the oil cooler. At a pressure difference of 55 psi (3.7921 bar) to 65 psi (4.4815 bar) over the oil cooler, the valve opens and permits the pressure to decrease.
D. Generator Scavenge Pump The generator scavenge pump is a three element geroter pump installed on the lube module. This scavenge pump returns the generator oil to the APU gearbox sump through the generator filter assembly. The oil from the filter is directed against the wall of the gearbox. This removes the air which is mixed with the oil.
E. Magnetic Drain Plug The magnetic plug is a plug with a magnetic chip-detector that is immersed in the APU oil. This is installed into a check valve which prevents oil loss when the magnetic plug is removed for examination.
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F. De-Oil Solenoid Valve The de-oil solenoid valve is installed above the oil level in the APU gearbox. This permits air to enter the inlet of the oil supply pump for cold start conditions. The air makes sure that the oil supply pump can not prime until 60 % APU speed, this reduces pump drag. This drag slows the on APU acceleration time.
G. Oil Filler Ports The APU has a gravity fill port and a pressure fill port installed on the left side of the gearbox. You can put oil into the APU through either of the two fill ports.
H. Oil Sight Glass The oil sight glass is installed on the left side of the gearbox. ADD and FULL marks on the plate show when oil must be added.
6. Operation/Control and Indication
________________________________ When the APU start sequence is initiated (Ref. 49-42-00) the lube module gets oil from the oil reservoir. The oil passes to the oil cooler, then to the filter which retains any particles contained in the oil. The de-oil solenoid valve opens during start up to 60% rpm when:
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