Piper Cherokee Six Service Manual page 488

PIPER CHEROKEE SIX SERVICE MANUAL
NOTE
The latest systems
which employ
a central filter in
combination with a differential vacuum gauge will indicate a
decline in panel gauge reading when the filter becomes
clogged and vacuum declines below the recommended value.
The filters should be replaced when gauge reading declines
below the recommended value; do not adjust regulator.
d. Vacuum Regulator:
1. The vacuum regulating valve seldom needs replacement. Symptoms that suggest
replacement are:
(a) Chatter as indicated by rapid fluctuation of the vacuum gauge needle or an
audible sound.
(b) Non-repeatability of the vacuum gauge reading when the panel gauge is not
suspect or has been checked against a known test gauge (cruise RPM only).
2. All modes of regulator malfunction tend to increase the vacuum power applied
to the gyros. Thus, although excess vacuum is applied, a loss of vacuum does not occur.
3. The gyros themselves act as a limiting device to keep the vacuum power applied
from exceeding safe levels.
NOTE
If the panel gauge has been checked and found OK and the
vacuum gauge reading does not repeat within the range of 4.8
to 5.2 inches of mercury, then the regulating valve should be
changed. Observe the usual precautions
for maintaining
system cleanliness to avoid premature pump service.
9-5. TROUBLESHOOTING.
TABLE IX-I. VACUUM SYSTEM
NOTE
For Serial Numbers before 32-7100001 and 32-7140001.
Trouble
Cause Remedy
No vacuum pressure
Pump inoperative, dis- Replace pump. Locate
gauge indication.
connected. Broken or
trouble and correct.
restricted lines.
INSTRUMENTS
Revised: 8/7/74
2J20