Piper Arrow IV Turbo Maintenance Manual page 469

3. Gyro Filters:
A. Gyro filters must be serviced on a scheduled basis, not to exceed 100 hours, or sooner as condition
indicates.
B. The system installation employs a large central filter and differential vacuum gauge that
continuously monitors the filter condition while indicating vacuum readings.
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.
4. Vacuum Regulator:
A. The vacuum regulating valve seldom needs replacement. Symptoms that suggest replacement are:
(1) Chatter as indicated by rapid fluctuation of the vacuum gauge needle or an audible sound.
(2) 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).
B. 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.
C. The gyros themselves act as a limiting device to keep the vacuum power applied from exceeding
safe levels.
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.
VACUUM PUMP.
The vacuum pump is of the rotary vane, positive displacement type. This unit consists essentially of an
aluminum housing containing a tempered sleeve in which an offset rotor, with moving blades is incorporated.
This assembly is driven by means of a coupling mated to the engine driven gear assembly. The pump is
mounted on the accessory section of the engine.
PIPER AIRCRAFT
PA-28RT-201 / 201T
MAINTENANCE MANUAL
—NOTE—
—NOTE—
2H22
37-10-02
Page 37-04
Revised: August 18, 1980