TM55-2840-251-23
Section III PRINCIPLES OF OPERATION (Continued)
1-15 AIR SYSTEM
Pressure air is used to seal the bearing compartments
and to cool internal parts of the engine.
Compressor discharge pressure (P3) is directed to the
fuel control unit to provide a signal indicating change of
condition within the engine.
Compressor stall is prevented by the compressor bleed
valve. The bleed valve consists of a piston and rolling
diaphragm operating within a housing under opposing
pressures. The bleed valve is secured by two bolts to
an outlet port on the gas generator case which provides
a direct passage for the flow of compressor interstage
air (P2.5) to the bottom of the valve. Compressor
discharge air (P3) is tapped off and metered through an
orifice (adjustable in earlier engines and fixed in later
engines) in the cover of the unit, then passed through an
intermediate passage and out to atmosphere through
another orifice. The control pressure (Px) between the
two orifices acts upon the upper side of the piston, so
that when Px is greater than P2.5 the bleed valve
closes.
END OF SECTION
1-20
