Piper CHEROKEE ARCHER II Pilot Operating Handbook page 125

PIPER
AIRCRAFT CORJORATION
PA.28.T8I, CHEROKEE ARCHER
II
SECTION
7
DESCRITTION AND OPERATION
7.17
VACUUM SYSTEM
The vacuum system
is
desigrred
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
fiiter
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
sheai 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
pr.essure
in
a
system that
has
remained constant over an extended period may indicate
a
dirty filter, dirty
screens,
possibly
a
sticking
vacuurn 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 ryros. The valve is set so the normal
vacuum reads 5.0
t
.l
inches
of mercury,
a
setting
which provides
sufficient vacuuln to
operate
all the gyros
at their rated RPM. Hieher
settings
will
damage
the gyros and
with
a
low
setting
the gyros
will
be unreliable.
The
regplator is located behind the instrument panel and is
accessible
from below the instrument
panel.
REPTORT:
V8790
7-15
IISUED: JTINE
18,lYl6