7.19 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 engine
from damage. If the drive shears, the gyros will become inoperative.
A vacuum gauge mounted on the upper left 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.
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
PIPER AIRCRAFT CORPORATION
SECTION 7
PA-38-112, TOMAHAWK
DESCRIPTION & OPERATION
ISSUED: JANUARY 20, 1978
REPORT: 2126
7-15
7.19 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 engine
from damage. If the drive shears, the gyros will become inoperative.
A vacuum gauge mounted on the upper left 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.
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
PIPER AIRCRAFT CORPORATION
SECTION 7
PA-38-112, TOMAHAWK
DESCRIPTION & OPERATION
ISSUED: JANUARY 20, 1978
REPORT: 2126
7-15