SECTION 7 CESSNA
AIRPLANE AND SYSTEMS DESCRIPTION MODEL 208B 867 SHP
GARMIN G1000
U.S.
FUEL SYSTEM (Continued)
FUEL BOOST PUMP SWITCH
An auxiliary boost pump switch, located on the left sidewall switch and
circuit breaker panel, is labeled FUEL BOOST and has OFF, NORM,
and ON positions. When the FUEL BOOST switch is in the OFF
position, the auxiliary boost pump is inoperative. When the FUEL
BOOST switch is in the NORM position, the auxiliary boost pump is
armed and will operate when fuel pressure in the fuel manifold
assembly drops below 2.5 psi. The NORM position is used for all
normal engine operation where main fuel flow is provided by the ejector
boost pump and the auxiliary boost pump is used as a standby. When
the FUEL BOOST switch is placed in the ON position, the auxiliary
boost pump will operate continuously and the motive flow pump will be
shut off. The ON position is used for engine start and any other time
that the auxiliary boost pump cycles on and off with the switch in the
NORM position due to low fuel pressure.
The high pressure motive flow shutoff valve needs to be closed (FUEL
BOOST switch ON) during engine starts so there is sufficient fuel
pressure delivered to the Fuel Control Unit to open the minimum
pressurizing valve to allow fuel flow to the fuel nozzles. The fuel boost
pump incorporates a timer so when the fuel boost pump switch is
moved from ON to NORM or OFF the pump will continue to run for a
short period of time. This is to avoid the motive flow shutoff valve from
opening and the pump switching off at the same time. This prevents
potential low fuel pressure to the engine causing the boost pump to
cycle back on.
If the FUEL BOOST pump switch is not turned ON prior to
engine start, (motive flow shutoff valve not energized) there
will be insufficient fuel pressure to open the minimum
pressurizing valve and the engine will not start.
208BPHCUS-00
7-82
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