TM 55-2840-241-23 Change 19          5-3 Section  II.   FUEL SYSTEM WARNING 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 system. WARNING Failure to properly install, align, and tight- en fuel fittings and tubes could result in an engine failure. 5-6.   General. 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: a. Disconnect the input lead to the ignition exciter. b. Disconnect the fuel hose at the fuel nozzle and place the open end in a suitable container. c. 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. d. 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 position. e. 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., P_r, P_g, P_y or ^Pc from tee fitting on governor to fuel control) is removed or disturbed during maintenance, check the control air tubing for leaks as follows: a. Disconnect the pressure sensing (P_c) line from the pressure probe elbow in the diffuser scroll. b. Apply 50-80 psi filtered air or nitrogen to P_c line. Air will immediately escape from the pressure regulating air valve port on the power turbine governor. c. 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. d. 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 P_c tube.    Tighten coupling nuts to 80-120 in. lb. Hold the P_c filter while tightening the cou- pling nut. During aircraft run up, use the soap solution to verify no leakage around the reconnected P_c line prior to flight. Rinse the soap and water solution from the engine after the check is completed. 5-9.   Fuel Pump.   a.  Removal.   (1) 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). (2) Disconnect the fuel supply hose at pump inlet (23). (3) 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. (4) 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- ing studs. (5) Remove and discard mounting flange gasket (32) and preformed packing (33). (6) If a new pump is to be installed, remove the tube fittings and keep them for installation in the new pump. Discard preformed packing. b.  Installation.