(overloading), action of the bleed-load control
t h e r m o s t a t a l l ow s t h e bu t t e r f l y va l ve t o c l o s e
The lubrication system is very simple; but, because
sufficiently to regulate bleed-air flow without causing
of the temperatures and rpm at which the unit operates,
engine shutdown or loss of engine speed.
positive feed oil pressure for lubrication and cooling
DIFFERENTIAL AIR PRESSURE
must be provided. The system includes a pressure and
R E G U L ATO R . -- T h e d i ff e r e n t i a l a i r p r e s s u r e
scavenge pump, an oil filter, an oil temperature
regulator, secured to the top of the turbine plenum,
regulator, an oil cooler, an oil tank, and an oil drain
solenoid valve (fig. 12-7). Oil under pressure is
provides a constant control-air pressure to the
unloading air shutoff valve under all conditions for
has been used, it collects in the common sump between
opening and closing of the valve.
the compressor and turbine assemblies and in the sump
LOAD CONTROL THERMOSTAT.--The load
of the accessory section; it is then returned, by the
control thermostat is mounted in the engine tail pipe. It
scavenge pump, to the oil tank.
If the temperature of the oil is such that it requires
thermostat and is connected to the load valve by a
cooling, it is routed through the oil cooler. Cooling is
control air line. It functions to control the bleed load in
accomplished by compressor inlet air flowing around
relation to EGT. At a specified temperature, the
the tubes of the oil cooler. If the temperature of the oil
thermostat valve opens and bleeds control air pressure
is not great enough to require cooling, a bypass valve in
from the actuator diaphragm of the load valve. This
the temperature regulator routes the oil directly to the
reduction in control air pressure allows the butterfly
oil tank, where it is again pumped through the engine.
valve to modulate, thereby maintaining the maximum
The unit is provided with an oil pressure actuated
permissible bleed load on the engine and preventing
switch, which prevents the engine from starting until
oil pressure builds up sufficiently to close the switch.
overheating of the engine.
COMPRESSOR AIR INLET
SCAVENGE PUMP PRESS
OIL VENT LINE
OIL PUMP PRESS
Figure 12-7.--Lubrication system.