the two drain ports located on the aft face of the filter
cover. Pressure taps are provided before and after
(labeled BF and AF) the filter element to permit mea-
surement of filter pressure drop if desired.
1-15. Double Check Valve.
The double check valve assembly is a mechanical
device placed in the governing pressure (Pg) circuit
between the power turbine governor and the main fuel
control to dampen surges in the Pg pressure signal.
(See figure 1-4.) It incorporates two individual,
diaphragm operated valves within one unit. The valves
are located in parallel with each other and open in
opposite directions. Movement of air through the check
valve assembly in either direction is permitted by one
of the valves. However, when a stable signal is pro-
vided, a very small flow of air is experienced with the
valve toward its closed position. Any pressure surges in
the Pg signal will be dampened by spring loading on
1-16. Pc Air Filter.
The Pc air filter is a 10 micron filter located in the Pc
air supply line leading from the diffuser scroll to the
power turbine governor. It incorporates a permanent
type, wire mesh, cleanable element. It prevents the
governor and fuel control pneumatic components from
being contaminated with foreign particles by filtering
Pc air flow to the governor and control.
1-17. Fuel Check Valve.
The fuel check valve is located in the fuel line
between the fuel control and the fuel nozzle. It has a
cracking pressure of 22-28 psi and serves to prevent
leakage of fuel through the fuel nozzle into the combus-
tion chamber if the fuel cutoff valve is inadvertently
opened or leaks while the engine is not operating.
1-18. Fuel Nozzle.
The fuel nozzle is a single-entry, dual-orifice type
unit. It contains an integral valve for dividing primary
and secondary flow. This fuel nozzle relies on the fuel
check valve to provide fuel cutoff when the fuel mani-
fold pressure falls below a pre-determined pressure, to
keep fuel out of the combustion chamber at shutdown.
1-19. Lubrication System.
The lubrication system is a dry sump type with an
external reservoir and heat exchanger. A gear type
pressure and scavenge pump assembly is mounted
within the power and accessory gearbox. (See figures
1-6 and 1-7.) The oil filter, filter bypass valve, and pres-
sure regulating valve are in a unit which is located in
the upper right-hand side of the power and accessory
gearbox housing and are accessible from the top of the
engine. A check valve is located between the housing
and the filter unit. Indicating type magnetic chip
detectors are installed at the bottom of the power and
accessory gearbox, and at the engine oil outlet connec-
tion. All engine oil system lines and connections are
internal with the exception of pressure and scavenge
lines to the compressor front support, the gas producer
turbine support, and the power turbine support.
1-20. Ignition System.
The engine ignition system consists of a low tension
capacitor discharge ignition exciter, a spark igniter
lead, and a shunted-surface gap spark igniter. The
system receives its input power from a 14 to 29-volt, d-c
1-21. Temperature Measurement System.
The temperature measurement system has four
chromel-alumel single junction thermocouples in the
gas producer turbine outlet (TOT) and a associated
integral harness. The voltages of the four thermocou-
ples are electrically averaged in the assembly and
delivered by the assembly lead to an engine terminal
block for attachment to the airframe temperature indi-
1-22. Anti-king System.
a. Anti-icing is provided for the compressor inlet
guide vanes and front support hub by the use of com-
pressor discharge air. The air is taken from a port at
the twelve oclock position on the front face of the dif-
fuser scroll. An anti-icing air shutoff valve is installed
in the port and is manually operated from the flight
deck to control anti-icing airflow. Anti-icing air tubes
direct the flow of air from the valve to fittings on each
side of the compressor front support. The air is then
routed through an annulus around the OD of the front
support and through the inlet guide vanes and is dis-
charged into the inlet air stream.
b. The approximate effects of anti-icing air flow on
performance available to pilot at power levels above
40,000 N1 (gas producer) speed are immediate and