-
the APU speed is between 0% and 60% and the oil sump temperature is below -6.7.C (20.F),
-
the APU speed is between 95% and 7% during the APU shutdown
sequence,
-
the aircraft altitude is more than 30.000 ft.
4. Interface
_________
The Storage and distribution system has interface with:
-
the Accessory Cooling System (Ref. 49-52-00),
-
the APU Control and Monitoring System (Ref. 49-61-00),
-
the Oil Indicating System (Ref. 49-93-00),
-
the Low Oil Pressure and the High Oil Temperature Warning System (Ref. 49-94-00).
5. Component Description
_____________________
A. Oil Pump
(Ref. Fig. 002)
The oil pump assembly is made up of:
-
a high-pressure pump (driven together with the scavenge pump),
-
a scavenge pump (for the turbine bearing),
-an oil filter,
-
a differential pressure indicator,
-
a high-pressure relief valve,
-
a pressure regulator valve.
(1)
This pump is a dual-element unit that is assembled as a module into a housing which 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 relief-valve is of the poppet and seat type. It is installed in parallel to the lubrication items and opens at a pressure difference of 200 psi (13.7895 bar) over the items.
(3)
The oil pressure regulation-valve is of the spool and sleeve type. It is installed in parallel to the lubrication elements and controls the oil pressure 65 +5 -5 psi (4.4815 +0.3447 -0.3447 bar).
B. Oil Filters
(Ref. Fig. 002)
The main components of the oil filter are:
-
the filter housing,
-
the filter element,
-
the differential pressure indicator,
-
the differential pressure bypass valve,
-
the differential pressure switch. 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 indicator button that pops out when the
filter is clogged. When this occurs, it is necessary to change the
filter.
A differential pressure of 1.4 bar (20 PSI) between the inlet and the
outlet of the filter causes the indicator button (which is colored red)
to come out.
The differential-pressure bypass valve opens when the pressure increases
to more than 60 PSI.
The differential pressure switch is installed in the filter housing. It
transmitts a signal to the ECB if the filter element is clogged.
C. Oil Cooler (Ref. Fig. 001) The main components of the oil cooler are:
-
the oil cooler housing,
-
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 in the oil cooler inlet. It helps to increases the oil temperature quickly and keeps it high enough to prevent moisture instrution. The valve begins to close at an oil temperature of 60.C (140.F) and the oil flows through the oil cooler. At a pressure difference of 50 PSI (3.5 bar) over the oil cooler, the valve opens and permits the pressure to decrease.
D. Generator Scavenge Pump (Ref. Fig. 002) The generator scavenge pump is a fixed-clearance gear pump installed on the APU gearbox. 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 (Ref. Fig. 003) 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.
F. De-Oil Solenoid Valve The de-oil port and solenoid valve are installed above the oil level in the APU gearbox. These permit 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, which reduces pump drag. This drag has a bad effect on APU acceleration time.
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