TM 9-4520-258-14
1-13. FUEL SYSTEM - continued.
(1)
Priming the fuel system is accomplished by turning the MODE SWITCH (S1) to the VENT position and
holding the PURGE SWITCH (S4) to the ON position until the fuel pressure gage indicates greater than zero.
When S4 is released, the pressure must be greater than 10 psi.
(2)
If not, purging must be continued until the proper fuel pressure is obtained. Priming the fuel system at
extremely low ambient temperatures with the correct fuels presents no problems, except it takes slightly
longer due to the greater restriction of cold fuel circulating through the filter.
(3)
The purge system can also be used to transfer fuel from an external source to the internal fuel tank. The
external fuel hose must be attached to the external fuel supply connection and the fuel transfer valve (V1)
must be in the EXTERNAL TANK position. When the PURGE SWITCH (S4) is operated, the fuel passes
through the pump to the 3-way solenoid purge valve (L2) to the purge line and into the internal fuel tank. Do
not over fill the tank.
c.
Ventilation Mode. In the VENT mode, fuel is drawn through the low pressure filter by the fuel pump. The fuel is then
pumped through the two-way fuel solenoid valve (L1), to the 3-way solenoid purge valve (L2). Since L2 is not energized,
the fuel passes through the normally open (N.O.) position of L2 and returns to the inlet side of the fuel pump. If L2 is
energized, the unit will operate as described in the preceding paragraph, Purge System.
d.
Heating Mode. In the heating mode, fuel flow is the same as during vent mode. Upon heat demand, fuel solenoid
valve (LI) closes and fuel is supplied to the nozzle at the set pressure. Unused fuel is bypassed back to the pump
through the secondary bypass line. When desired air temperature is reached or the temperature limit switch (S2)
activates or the safety relay (K1) activates, LI opens. When LI is open all fuel will return to the pump through the primary
bypass line.
e.
Additional Components. Additional components of the fuel system are:
(1)
The fuel tank drain, provides a means to drain the tank when required.
(2)
The fuel tank gage, mechanically indicates the level of fuel in the internal fuel tank.
(3)
The fuel filler neck, provides a means to service the fuel tank with fuel. A fuel strainer is located inside the
neck to trap foreign objects before they enter the tank. The screen can be removed and cleaned for reuse.
(4)
The fuel pressure gage, indicates purge, recirculate, and heat fuel pressures.
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