Piper Cherokee Six - Page 487

PIPER
CHEROKEE
SIX
SERVICE
MANUAL
b.
Vacuum
Gauges:
1.
Vacuum
gauges
seldom
require
service
and
usually
are
replaced
when
malfunctions
occur.
NOTE
Vacuum
gauge
failure
in
a
properly
operating
vacuum
system
does
not
impair
safety
of
flight.
2.
If
the
vacuum
gauge
malfunctions
in
a
manner
to
cause
an
incorrect
reading
in
normal
cruise
conditions,
the
gauge
must
be
checked
by
comparing
the
reading
with
a
gauge
of
known
accuracy.
If
the
gauge
is
indicating
correct
values
and
the
system
vacuum
level
is
not
in
accordance
with
the
specified
vacuum,
then
and
only
then
should
the
regulator
be
reset.
3.
Visual
examination
of
the
gauge
performance
should
cover
the
following
steps:
(a)
With
engine
stopped
and
no
vacuum
applied
to
the
gauge,
its
pointer
should
rest
against
the
internal
stop
in
the
9
o'clock
position.
Any
other
displacement
from
this
position
suggests
need
for
replacement.
(b)
A
slight
overshoot
during
engine
startup,
not
to
exceed
half
an
inch
(1/2")
of
mercury,
is
normal
and
is
not
cause
to
replace
gauge.
(c)
With
engine
operating
at
normal
cruise
RPM,
the
gauge
should
read
from
4.9
inches
to
5.1
inches
of
mercury
(vacuum).
(d)
At
1200
RPM,
the
vacuum
gauge
reading
should
be
more
than
four
inches
of
mercury.
c.
Gvro
Filters:
1.
Gyro
filters
must
be
serviced
on
a
scheduled
basis,
not
to
exceed
100
hours,
or
sooner
as
condition
indicates.
NOTE
Several
gyro
filter
systems
have
been
used
on
various
aircraft,
depending
on
when
the
aircraft
was
built.
2.
The
oldest
aircraft
installations
generally
did
not
have
central
filters.
They
depended
on
the
small
cloth
or
paper
disc-type
filters
built
into
the
instruments
themselves.
This
type
of
filter
requires
frequent
replacement
for
proper
gyro
operation.
3.
The
later
system
installation
employed
a
large
central
filter
which
eliminated
the
frequent
replacement
of
the
small
internal
filters
in
the
gyros.
4.
The
latest
system
installation
employs
a
large
central
filter
and
differential
vacuum
gauge
that
continuously
monitors
the
filter
condition
while
indicating
vacuum
readings.
NOTE
In
the
aircraft
systems
described
in
Items
(2)
and
(3)
above,
failure
to
replace
filters
would
cause
a
slight
increase
in
vacuum
gauge
readings.
The
AIRBORNE
regulator
will
automatically
adjust
to
the
flow
changes
that
result
when
dirty
filters
are
allowed
to
remain
in
the
system.
INSTRUMENTS
Revised:
8/7/74
2J19