Piper Cherokee Arrow II Pilots Operating Manual page 35

ARROW I1
Secondary power is provided by a 12-volt, 25-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 master switch 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 maximum 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.
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 which eliminates the need for an airloil 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 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 f .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.
*Serial nos. 7535001 and up
2-14
AIRPLANE AND SYSTEMS
REVISED: JUNE 18,1974