Piper Arrow IV Turbo Maintenance Manual page 300

A fuel tank selector allows the pilot to control the flow of fuel to the engine, and is located on the left side
wall below the instrument panel. It has three positions: OFF, LEFT TANK and RIGHT TANK. The arrow on
the handle of the selector points to the tank which is supplying fuel to the engine. The vapor return from the
engine is also routed back to the tank selected. When the selector valve is in the OFF position, vapor return is
routed back to the right fuel tank. The valve also incorporates a safety latch which prevents inadvertently
selecting the "OFF" position.
The engine fuel injection system is a "continuous flow" type, which utilizes a vapor return line leading
back to the fuel tanks. This line provides a route back to the tanks for vapor laden fuel that has been separated
in the injector pump swirl chamber. The engine has an engine driven fuel pump that is a part of the fuel
injection system. An auxiliary fuel system is provided. The purpose of the electrically powered auxiliary fuel
system is to supply fuel to the engine in case of engine driven fuel pump shaft failure or malfunction, for
ground and inflight engine starting, and for vapor suppression. The auxiliary fuel pump switch is located on
the instrument panel above the engine control quadrant, and is a three position rocker switch; LO, HI and OFF.
The LO auxiliary fuel pressure is selected by pushing the top of the switch. The HI auxiliary fuel pressure is
selected by pushing the bottom of the switch, but this can be done only after unlatching the adjacent guard.
When the HI auxiliary fuel pump is activated, an amber light near the annunciation panel is illuminated. This
light dims whenever the pump pressure reduces automatically and manifold pressure is below approximately
21 inches.
In case of a failed engine driven fuel pump, the auxiliary electric fuel pump should be set on HI. Adequate
pressure and fuel flow will be supplied for up to approximately 75% power. Manual leaning to the correct fuel
flow will be required at altitudes above 15,000 feet and for engine speeds less than 2300 RPM. An absolute
pressure switch automatically selects a lower fuel pressure when the throttle is reduced below 21" Hg manifold
pressure and the HI auxiliary fuel pump is on.
Excessive fuel pressure and very rich fuel/air mixtures will occur
if the HI position is energized when the engine fuel injection
system is functioning normally.
Low auxiliary fuel pressure is available and may be used during normal engine operation both on the
ground and inflight for vapor suppression should it be necessary as evidenced by unstable engine operation or
fluctuating fuel flow indications during idle or at high altitudes.
A spring loaded OFF primer button switch, located on the instrument panel and is used to select HI
auxiliary fuel pump operation for priming, irrespective of other switch positions. The primer button may be
used for both hot or cold engine starts.
On airplanes equipped with an optional engine primer system (identified by Placard below primer button
shown in Figure 28-3), the primer switch location and actuation is the same as the basic airplane. However,
this system does provide a separate primer system as an integral part of the engine fuel system. An electrically
operated diverter valve is located in the metered fuel supply line between the air throttle valve and the
manifold valve. Other components are two primer nozzles, located in the intake manifold on each side of the
engine, the interconnecting fuel lines, and fine wire spark plugs. Actuation of the engine primer switch
operates the auxiliary electric fuel pump on HI and energizes the diverter valve which supplies fuel to each
primer nozzle. The diverter valve does not shut off all fuel flow to the manifold valve, therefore some quantity
of fuel is also supplied to each cylinder nozzle during priming. Operation of the auxiliary fuel pump on HI and
LO is unchanged.
PIPER AIRCRAFT
PA-28RT-201 / 201T
MAINTENANCE MANUAL
—NOTE—
2A21
28-00-01
Page 28-02
December 1, 1978