Vacuum System Service Tips - Piper Dakota Maintenance Manual

DISTRIBUTION

VACUUM SYSTEM SERVICE TIPS

When replacing any threaded fittings, DO NOT USE PIPE
DOPE or any other anti-seize tape or compound. The
AIRBORNE fittings are all cadmium plated to avoid the need for
any other anti-seize materials.
This information will aid in diagnosing vacuum system problems with hoses, clamps, filters, regulating
valves, and gauges.
l. Hoses and Clamps:
a. Inspect hoses and clamps whenever they are disconnected.
b. Inspect hose ends for rubber separation and slivers of rubber inside of tube.
c. Replace broken, damaged, or corroded hose clamps and fittings.
2. Vacuum Gauges:
a. Vacuum gauges seldom require service and usually are replaced when malfunctions occur.
Vacuum gauge failure in a properly operating vacuum system
does not impair safety of flight.
b. If vacuum gauge malfunction causes an incorrect reading in normal cruise flight, check gauge by
comparing reading with a gauge of known accuracy. If the gauge is indicating correct values and
the system vacuum level is not as specified, reset the regulator.
c. Visually examine gauge performance as follows:
(1) With engine stopped and no vacuum applied to gauge, pointer should rest against the internal
stop in 9 o'clock position. Any other displacement indicates need for replacement.
(2) A slight overshoot during engine startup, not to exceed one-half inch of mercury, is normal
and not cause to replace gauge.
(3) With engine operating at normal cruise rpm, gauge should read from 4.8 inches to 5.2 inches
of mercury (vacuum).
(4) At 1200 rpm, vacuum gauge reading must be more than 4 inches of mercury.
PIPER AIRCRAFT
PA-28-236
MAINTENANCE MANUAL
—CAUTION—
—NOTE—
2E6
37 - 11 - 00
Page 37 - 04
Reissued: August 1, 1986