3. Service gyro filters on a scheduled basis, not to exceed 100 hours, or as conditions indicate. The
system comprises a large central filter and differential vacuum gauge that continuously monitors filter
condition while indicating vacuum readings.
—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 filter becomes clogged and vacuum declines
below recommended value. Filters should be replaced when
gauge reading declines below recommended value; do not adjust
regulator.
4. Vacuum Regulator:
a. Vacuum regulating valves seldom need replacement. Symptoms that suggest replacement are:
(1) Chatter as indicated by rapid fluctuation of vacuum gauge needle or an audible sound.
(2) Non-repeatability of vacuum gauge reading when panel gauge is not suspect or has been
checked against a known test gauge (cruise rpm only).
b. All modes of regulator malfunction tend to increase vacuum power applied to gyros.
c. The gyros act as a limiting device to keep vacuum power applied from exceeding safe levels.
—NOTE—
If the panel gauge is operating properly and vacuum gauge
reading does not repeat within the range of 4.8 to 5.2 inches of
mercury, change regulating valve
VACUUM PUMP
The vacuum pump is a rotary vane, positive displacement pump. It consists of an aluminum housing
containing a tempered sleeve in which an offset rotor, with moving blades is incorporated. This assembly is
driven by a coupling mated to engine driven gear assembly. The pump is mounted on the accessory section of
the engine.
REMOVAL OF VACUUM PUMP
1. Remove top portion of engine cowling. (Refer to chapter 71.)
2. Loosen hose clamp and remove hose from pump fitting.
3. Remove four retaining nuts, lock washers, and plain washers securing pump to engine.
4 Remove vacuum pump.
37 - 12 - 00
Page 37 - 05
Reissued: August 1, 1986
2E7
PIPER AIRCRAFT
PA-28-236
MAINTENANCE MANUAL
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