-pressure = 55 psi (3.7921 bar) to 65 psi (4.4815 bar). The spring loaded pressure relief valve opens when the pump pressure increases to more than 65 +10 -0 psi (4.4815 +0.6894 -0.0000 bar) Thus the oil returns to the oil sump.
B. Oil Filters
The main components of the oil filters are:
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the filter housing,
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the 20 micron disposable cartridge,
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the differential pressure switch and indicator on the lubrication oil-filter,
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the differential pressure switch and indicator on the generator scavenge oil-filter,
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the filter bypass valve.
The two oil filters are installed in the APU oil system, one for high-pressure supply and one for the generator oil scavenge. The two filters 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 30 - 35 PSI between the inlet and the outlet of the filter causes the indicator button to pop out. Additionally, the scavenge filter and the lubrication filter have an electrical switch which gives signals to the ECB. The filter bypass valve opens if the pressure in the filter increases to more than 50 +10 -0 psi (3.4473 +0.6894 -0.0000 bar).
C. Oil Cooler The main components of the oil cooler are:
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the oil cooler housing,
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the check valve,
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the bypass valve,
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the drain plug. The oil cooler is a tube type air-oil heat exchanger. The oil flows through tubes that are installed inside a housing. A cooling fan blows air across the tubes to an outlet. This removes the heat that has been transferred from the oil to the tubes. The oil cooler bypass valve starts to open when the oil pressure in the oil cooler is more than 30 psi (2.0684 bar) and is fully open by 50 psi (3.4473 bar).
D. Generator Scavenge Pump The main components of the generator scavenge pump are:
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the pump housing,
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the pump rotor,
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the vanes.
The oil pressure pump is a vane type unit consisting of a slotted inner
rotor equipped with vanes, a precision ground cam profile and a housing
body.
The flow of the pump is 36 l.min (9.5101 USgal.mn).
E. Rear Bearing Scavenge Pump The rear bearing scavenge pump is a gerotor positive displacement pump units consisting of two elements, an inner and an outer rotor. The inner rotor has one less tooth than the outer, and has its centerline positioned at a fixed eccentricity from the centerline of the outer element. The inner element is driven by one pinion of the gearbox. The flow of the pump is 2.6 l.min (0.6868 USgal.mn)
F. 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.
G. De-Oiling 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 55% APU speed, which reduces pump drag. This drag slows the APU acceleration time due to the high viscosity of cold oil.
H. Oil Filler Ports
The APU has a gravity fill port installed on the left side of the
gearbox. You can put oil into the APU through fill port.
J. Sight Glass The sight glass is installed on the left side of the gearbox. It has a glass sheet that is sandwiched and sealed. The plate has a hole to permit vision of the oil through the glass. The ADD and FULL marks on the plate show when oil must be added.
6. Operation/Control and Indication
________________________________ (Ref. Fig. 002) The mechanically driven oil pressure pump removes the oil from the oil reservoir by suction. The oil passes to the oil cooler, then to the filter which retains any particles contained in the oil. The ECB energizes the de-oiling solenoid valve during the APU start sequence. Thus opens the valve and air enters the oil pressure pump to reduce the load on this pump. Above 55% APU speed, the ECB de-energizes the solenoid and the de-oiling valve closes. The oil lubricates and cools the following components:
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the AC APU generator and its splines,
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the cooling fan splines,
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the gearbox gears and bearings,
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the front bearing,
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the rear bearing.
The gravity returns the scavenge oil from the APU generator, the splines,
the gearbox gears and the front bearing to the oil reservoir. Two
mechanically driven scavenge pumps removes the scavenge oil from the rear
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