Piper Navajo PA-31 Service Manual page 654

PIPER NAVAJO SERVICE MANUAL
h. Should the gauge reading not be within tolerance, first ascertain that the de-icer
boots have been pressure tested by the following procedure:
1. Use a source of clean 18 to 20 psig air with a testing rig consisting of:
(a) Adjustable regulator.
(b) Pressure gauge.
(c) Shut-off valve. (The shut-off valve is to be connected so as to trap air in the
De-Icer system.)
2. Attach test rig to the inlet port of either control valve. Disconnect the tubing
from the overboard port and cap this port. Apply 18 psig to the system, and, using the
shut-off valve, trap the pressure in this portion of the system. A soap solution may be used
to check for leakage, which should not exceed 3 psig per minute. This test need be run in
one nacelle only.
3. Check the pressure switch operation with the De-Icer system under pressure,
while the battery switch is in the "ON" position; the indicator light will glow.
4. With the master switch "ON" and the De-Icer control switch in "OFF" position,
press the indicator light to check the circuit and light bulb. If the indicator light does not
function, check and reset circuit breaker; a short circuit may exist.
5. Remove the test rig, lubricate threads, replace and tighten items dismantled.
i.
With the boot pressure test completed, recheck pressures as given in steps f and g.
j.
Should this reading not be within tolerance, shut-down the engine, loosen the jam
nut of the aft regulator of the dual regulators and turn the screw clockwise to increase
pressure or counterclockwise to decrease pressure.
k. Operate both engines, turn on de-icer switch and ascertain that the pressure gauge
surges to 18 ± .50 psi.
1. With both engines operating at 2500 RPM, check if pressure gauge located in the
right side of the instrument panel indicates 5.7 inches of mercury.
m. Should the gauge not indicate the correct reading, adjust the pneumatic relay valve
located forward of the instrument panel above the control pedestal.
1. To adjust the non-electrically controlled relay valve (Refer to Figure 10-7),
loosen the locking screw on the side of the relay valve with an Allen wrench and turn the
adjustment screw to obtain a correct reading with engines operating at 2500 RPM.
2. To adjust the electrically controlled relay valve (Refer to Figure 10-7), use the
following procedure:
(a) Remove co-pilot gyro pressure line from relay valve.
(b) Install "tee" fitting between relay valve and pressure line, using a short hose
on the valve side of the "tee" fitting to facilitate installation.
(c) Connect an accurate gauge with a range of 0 to 20 psi to the "tee" fitting
with a hose long enough to allow the face of the gauge to be observed from
the cockpit.
(d) Clamp hose connections to prevent leakage.
(e) Run engines at 2500 RPM and adjust co-pilot side of relay valve to obtain
5.7 inches of mercury on the test gauge.
(f) Lock adjustment on relay valve and remove test gauge.
(g) Reinstall gyro pressure line to relay-valve.
(h) Run engines 2500 RPM and adjust pilot side of relay valve to obtain 5.7
inches of mercury on the instrument panel gauge.
(i) Run engines at 2500 RPM and adjust orifice to obtain 5.7 inches of mercury
for pilot's gyros (indication on panel gauge) during boot inflation.
Reissued: 10/12/79
INSTRUMENTS
3D16