Piper PA-28-236 DAKOTA, Pilot Operating Handbook

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SECTION 7 PIPER AIRCRAFT CORPORATION
DESCRIPTION & OPERATION PA-28-236, DAKOTA
REPORT: VB-910 ISSUED: JUNE 1, 1978
7-16 REVISED: NOVEMBER 22, 1982
7.19 VACUUM SYSTEM*
The vacuum system operates the air driven gyro instruments. This
system consists of an engine-driven vacuum pump, a vacuum regulator, a
filter, a vacuum gauge, the necessary plumbing, and, when installed, the
directional and attitude gyro instruments.
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.
The vacuum gauge, mounted on the right instrument panel to the right
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 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.
7.21 INSTRUMENT PANEL
The instrument panel accommodates the customary advanced flight
instruments and the normally required power plant instruments (Figure
7-15). The artificial horizon and directional gyro are vacuum operated
through use of a vacuum pump installed on the engine, while the turn and
bank instrument is electrically operated. A vacuum gauge is mounted on
the far right side of the instrument panel. The radios and circuit breakers
are on the right-hand instrument panel, and extra circuits are provided for
the addition of optional radio equipment. An optional radio master switch
is located near the top of the instrument panel between the radio stacks.
It controls the power to all radios through the aircraft master switch. An
emergency bus
*Optional equipment