Piper Navajo PA-31 Service Manual page 639

PIPER NAVAJO SERVICE MANUAL
The two fuel quantity
gauges are calibrated in fractional divisions of one-fourth,
one-half, three-fourths and full. Dual transmitter units are installed in series in each fuel
cell.
This unit contains a resistance strip and a movable control arm. The position of this arm
is
controlled by a float in the fuel cell and this position is transmitted electrically to the
indicator gauge to show the amount of fuel in the cell. The quantity gauges will indicate
the
amount of fuel in the cell to which the fuel control levers are positioned. When the
fuel
control levers are moved to the "OFF" position, the quantity gauges will indicate fuel
level
of the cell last selected.
The dual exhaust temperature gauge of the turbo powered PA-31 indicates, in degrees
Fahrenheit, the temperature of the exhaust gases as they pass through the exhaust manifold
of each engine. The sender unit for this instrument is a thermocoupler type probe installed
in a threaded hole in each manifold.
The oil pressure, oil temperature and cylinder head temperature is a combination gauge,
each a complete unit within itself. The oil pressure unit (non-electrical) is connected to
the
pressurized oil passage of its respective engine. The oil temperature and cylinder
head
temperatures utilize a ratiometer to control each unit, both of which are connected with
the
airplane electrical system.
The engine hour recorder operates in conjunction with a pressure switch installed on the
right engine. Engine oil pressure actuates the switch, thus recording actual running
time
regardless of engine RPM.
The cowl flap, wing flap and trim position indicator are separate instruments, each with
their respective rheostat type sender units. Each sender unit is further described and their
adjustment procedures given in their related sections in this manual.
10-7. MISCELLANEOUS INSTRUMENTS. The magnetic compass installed in the PA-31
is
a self-contained instrument and is mounted above the instrument panel on the windshield
centerstrip. This instrument has an individual light which is connected to the instrument
lighting circuit. The compass correction card is located in the card holder mounted above
the compass.
The clock is a hand wound, 8-day time piece. It incorporates a stem wind with the knob
at the lower left-hand side of the dial. This knob, when pulled and turned, also adjusts the
hands. In addition two dummy hands are controlled by a center knob and they function as
elapsed time hands.
The dual tachometer provides an indication of crankshaft speed in revolutions per
minute for each engine. The tachometer connects to each engine accessory section by a
flexible drive cable. The drive operates a magnetic drag mechanism that gives smooth
operation, practically eliminating all pointer oscillation.
The dual manifold pressure gauge is a direct reading pressure instrument that indicates
manifold pressure graduated in inches of mercury. As the pressure in the intake manifolds
increases or decreases, the evacuated diaphragms contract or expand, moving the respective
pointers through a mechanical linkage.
The dual fuel pressure instrument of the turbo powered PA-31 is a differential pressure
gauge comprised of diaphragm sensing units with sector and pinion movement to amplify
diaphragm movement. The gauge indicates fuel pressure in pounds per square inch by
measuring differential pressure between the injector inlet versus deck pressure.
The dual fuel flow instrument incorporates the same differential diaphragm movement
as the fuel pressure gauge and indicates fuel flow in gallons per hour by measuring
differential pressure between the injector outlet versus deck pressure.
Reissued: 10/12/79
INSTRUMENTS
3D1