CIRCUIT BREAKER PANEL
Figure 7-13
7.17 VACUUM SYSTEM*
The vacuum system is designed to operate the air driven gyro instruments. This includes the
directional and attitude gyros when installed. The system consists of an engine driven vacuum pump, a
vacuum regulator, a filter and the necessary plumbing.
The vacuum pump is a dry type pump. A shear drive protects the pump from damage. If the drive
shears, the gyros will become inoperative.
A vacuum gauge, mounted on the far right instrument panel provides a pilot check for the system
during operation. A decrease in pressure in a system that remained constant over an extended period may
indicate a dirty filter, dirty screens, possibly a sticky vacuum regulator or leak in the system (a low vacuum
indicator light is provided in the annunciator panel). Zero pressure would indicate a sheared pump drive,
defective pump, possibly a defective gauge or collapsed line. In the event of any gauge variation from the
norm, the pilot should have a mechanic check the system to prevent possible damage to the system
components or eventual failure of the system.
A vacuum regulator is provided in the system to protect the gyros. The valve is set so the normal
vacuum reads 5.0 ± .1 inches of mercury, a setting which provides sufficient vacuum to operate all the gyros
at their rated RPM. Higher settings will damage the gyros and with a low setting the gyros will be unreliable.
The regulator is located behind the instrument panel. Vacuum pressure, even though set correctly, can read
lower at very high altitude (above 12,000 ft), and at low engine RPM (usually on approach or during
training maneuvers. This is normal and should not be considered a malfunction.
*Optional equipment
ISSUED: DECEMBER 16, 1976
REPORT: VB-880
7-15
PIPER AIRCRAFT CORPORATION
SECTION 7
PA-28-161, CHEROKEE WARRIOR II
DESCRIPTION AND OPERATION
Summary of Contents for CHEROKEE WARRIOR II
Page 253: ...Piper PA 28 161 28 7916159 N3067D ...