Piper Navajo PA-31 Service Manual page 644

PIPER NAVAJO SERVICE MANUAL
10-14. GYRO PNEUMATIC SYSTEM.
10-15. DESCRIPTION. The PA-31 uses a dry pneumatic pump system consisting of two
engine driven pneumatic pumps, pressure relief valves, inline filters, manifold and check
valve assembly, pneumatic relay, and necessary tubing, hoses, and connections. The system
operates at a pressure of between 4.3 and 6.1 inches of mercury. Gyro pressure is read on
the gauge located in the right side of the instrument panel. Also incorporated in the gauge
are two red buttons which indicate if either pneumatic system fails.
10-16. PNEUMATIC SYSTEM SET-UP PROCEDURE. The pneumatic system set-up
procedures given in these instructions cover five combinations of instrument and accessory
installations. These are as follows: Single Attitude and Directional Gyro Installation, Dual
Attitude and Directional Gyro Installation, Single or Dual Attitude and Directional Gyro
with H-14 Autopilot, and Single or Dual Attitude and Directional Gyro with Deicer Boots
and H-14 Autopilot. Before attempting any adjustments, ascertain that all line connections
are tight.
NOTE
Insure engines are up to operating temperature prior to
checking or adjusting the pneumatic system.
WARNING
Do not make adjustments of the regulators that are within
the engine nacelles while engines are running.
10-17. SINGLE ATTITUDE AND DIRECTIONAL GYRO INSTALLATION. The required
reading at the pressure gauge located in the right side of the instrument panel should
indicate 5.5 inches of mercury during single and multi-engine operation. Each engine should
be operated separately at about 2200 RPM to determine if and which pressure regulator
requires adjustment. There is one regulator for each engine pump located in the right
forward side of each engine nacelle. (Refer to Figure 10-2a.) Adjustment procedures for either
regulator are as follows:
a. Remove the access plate to the regulator which is the center forward plate at the top
of the nacelle.
b. Loosen the jam nut at the top of the regulator and turn the adjustment screw
clockwise to increase pressure or counterclockwise to decrease pressure.
c. Operate one engine at 2200 RPM to ascertain that the gauge indicates 5.5 inches of
mercury. Shutdown engine and readjust if necessary.
d. Repeat the preceding step for the other engine.
e. Operate each engine separately and then both through their entire range to
determine that the reading is correct.
f. Tighten regulator jam nut and install access plates.
g. The pressure at 2200 RPM, multi-engine should be 5.5 ± .4 in. hg.
Reissued: 10/12/79
INSTRUMENTS
3D6