Vacuum System - Piper Cherokee Archer II Pilot Operating Handbook

PIPER AIRCRAFT CORPORATION
PA-28-18I, CHEROKEE ARCHER II
7.17 VACUUM SYSTEM
SECfION 7
DESCRIITION AND OPERATION
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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 pUl)1p, a
vacuum regulator, a filter and the necessary plumbing.
The vacuum pump is a dry type pump which eliminates the need for an air/oil separator and its
plumbing. A shear drive protects the pump from damage. If the drive shears, the gyros will become
inoperative.
The vacuum gauge, mounted on the right instrumen t panel to the righ t of the radios, provides valuable
information to the pilot about the operation of the vacuum system. A decrease in pressure in a system that
has remained constant over an extended period may indicate a dirty filter, dirty screens, possibly a sticking
vacuum regulator or leak in system (a low vacuum indicator ligh t 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 and is accessible from below the instrument panel.
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ISSUED: JUNE 18, 1976
REPORT: VB-790
7-15