disk cooling system. The engine is also equipped for cabin-pressurization air.
The following
subparagraphs describe the bleed air systems.
a.
The compressor bleed air system. Automatically opening a valve in the gas generator
case to spill interstage compressor air, the compressor bleed air system thereby prevents compressor stalls
at low engine speeds. The valve closes gradually as higher engine speeds are attained.
b.
Bearing compartment seals. Pressure air is used to seal the 1st, 2d, and 3d bearing
compartments and also to cool both the compressor and the power turbines.
c.
Turbine disk cooling system. The compressor and power turbine disks are both cooled
by compressor discharge air bled from the straightening vane area of the diffuser. It is then metered
through holes in the compressor turbine vane support into the turbine hub baffle, where it divides into
three paths. Some of the air is metered to cool the rear face of the compressor turbine disk, and some
to pressurize the bearing seals. The air is then led forward through passages in the compressor turbine
hub to cool the front face of the compressor turbine. A portion of this cooling air is also led through a
passage in the center of the interstage baffle to the rear face of the power turbine disk. The remaining
air is used to cool the front face of the power turbine disk. The cooling air from both of the turbine
disks is dissipated into the main gas stream flow to the atmosphere.
9.15.
LUBRICATION SYSTEM
The T74 engine oil system is designed to provide a constant supply of clean lubricating oil to
the engine bearings, reduction gears, torquemeter, propeller, and all accessory drive gears. The oil system
consists of the components covered in the following subparagraphs. A schematic of the -702 engine
lubrication system is illustrated in figure 9.13.
a.
The oil tank is part of the compressor inlet case. The tank has a total capacity of 2. 3
gallons of which 1.5 gallons are usable. This capacity allows for oil expansion of approximately 0.8
gallons.
The oil tank has an oil filler neck and a quantity dipstick and cap which protrudes
arrangement,
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