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PIPER AIRCRAFT CORPORATION
PA-28R-201, ARROW
7.17 ELECTRICAL SYSTEM (continued)
Secondary power is provided by a 12-volt, 35-ampere-hour battery.
The ammeter as installed does not show battery discharge; rather it
shows the electrical load placed on the system. With all the electrical
equipment off, and the battery master (BATT MASTR) and alternator
(ALTR) switches on, the ammeter will indicate the charging rate of the
battery. As each electrical unit is switched on, the ammeter will indicate the
total ampere draw of all the units including the battery. For example, the
average continuous load for night flying with radios on is about 30 amperes.
The 30 ampere value plus 2 amperes for charging the battery will then show
on the ammeter, indicating the alternator is functioning properly.
Solenoids, provided in the battery and starter circuits, are used to
control high current drain functions remotely from the cabin.
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 vacuum pump, 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 engine from
damage. If the drive shears the gyros will become inoperative.
The vacuum gauge, mounted on the right instrument panel, (refer to Figure
7-21) 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.
ISSUED: SEPTEMBER 15, 1988
SECTION 7
DESCR/OPERATION
REPORT: VB-1365
7-17
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