Change 19 5-3
Section II. FUEL SYSTEM
The fuel/air discharge is irritating and
highly flammable. Mechanics must take
suitable measures to protect their eyes
and prevent fire. Aircraft must be properly
grounded before working on the fuel/air
Failure to properly install, align, and tight-
en fuel fittings and tubes could result in an
Fuel system servicing includes removal and installa-
tion of the fuel pump, gas producer fuel control, power
turbine governor, fuel nozzle, and double check valve. In
addition, it includes fuel filter replacement, cleaning the
fuel nozzle, and adjusting the gas producer fuel control.
5-7. Bleeding the Fuel System.
Maintenance of the fuel system can result in air en-
trapment in the fuel lines and subsequent false starts.
Following maintenance, purge the air from the fuel sys-
tem as follows:
Disconnect the input lead to the ignition exciter.
Disconnect the fuel hose at the fuel nozzle and
place the open end in a suitable container.
Loosen the line to the inlet side of the fuel check
valve. Move the twist grip to the idle detent and motor
engine until fuel appears at the inlet side of the check
valve. Move the twist grip to the closed position. Recon-
nect the fuel line to the inlet side of the fuel check valve.
Move the twist grip to the idle detent and motor
engine until a solid stream of the fuel flows from the
disconnected fuel line. Move the twist grip to the closed
Reconnect the fuel hose to the fuel nozzle. Re-
connect the input lead to the ignition exciter.
5-8. Fuel System Pneumatic Leak Check.
If any fuel system control air tubing (i.e., Pr, Pg, Py or
from tee fitting on governor to fuel control) is removed
or disturbed during maintenance, check the control air
tubing for leaks as follows:
Disconnect the pressure sensing (Pc) line from
the pressure probe elbow in the diffuser scroll.
Apply 50-80 psi filtered air or nitrogen to Pc line.
Air will immediately escape from the pressure regulating
air valve port on the power turbine governor.
Use a liquid soap solution (item 1, table 2-2) to
check the air tubes for leakage. Cover and parting sur-
faces on the fuel control and governor which produce a
slight bubbling of soap solution do not represent a leak
of sufficient magnitude to warrant concern. These leaks
were present during original calibration and were com-
pensated for at that time.
Reduce the pressure to 20-22 psi (0.14-1.54 kg
sqcm) and, check the governor diaphragm for leakage.
No leakage is acceptable. If leakage is noted from the
governor diaphragm remove the safety wire from the
screws, back off screws and then torque to 8-11 inch lbs.
Let screws rest for 20 minutes and retorque to same
value. If after this is completed, the governor diaphragm
still leaks, replace governor.
e. Reconnect the Pc tube. Tighten coupling nuts to
80-120 in. lb. Hold the Pc filter while tightening the cou-
pling nut. During aircraft run up, use the soap solution to
verify no leakage around the reconnected Pc line prior to
flight. Rinse the soap and water solution from the engine
after the check is completed.
5-9. Fuel Pump.
Disconnect the before-filter and after-filter
pressure lines (25 and 27, figure 5-2) and the seal drain
line (26) from the fuel pump (24).
Disconnect the fuel supply hose at pump inlet
Remove fuel tubes (3 and 4) between the fuel
pump and control. It will not be necessary to disturb the
clamping arrangement between the tubes.
Remove the three self-locking nuts (29, fig-
ure 5-3) and washers (30) which secure the fuel pump
(31) to the gearbox. Remove the pump from the mount-
Remove and discard mounting flange gasket
(32) and preformed packing (33).
If a new pump is to be installed, remove the
tube fittings and keep them for installation in the new
pump. Discard preformed packing.