Piper SENECA III - Page 190

SECTION
7
PIPER
AIRCRAFT
CORPORATION
DESCRIPTION
&
OPERATION PA-34-220T,
SENECA
III
The
fuel
injection
system
is
a
"continuous
flow"
type
that
utilizes
a
vapor
return
line
leading
back
to
the
fuel tanks.
This line
provides
a
route
back
to
the
tanks
for
vapor
laden
fuel
that
has
been
separated
in
the
injector
pump
swirl chamber.
Each
engine
has
an
engine-driven fuel
pump
that
is
a
part
of
the
fuel
injection
system,
An
auxiliary
fuel
system
is
provided.
The
purpose
of
the
electrically
powered
auxiliary
fuel
system
is
to
supply
fuel
to
the
engine
in
case
of
engine-driven
fuel
pump
shaft
failure
or
malfunction.
for ground
and
inflight
engine
starting,
and
for
vapor
suppression.
The
two
auxiliary
fuel
pump
switches
are
located
on
the
lower
left
side of
the
instru-
ment
panel
and
are
three-position rocker
switches:
LO, HI
and
OFF. The
LO
auxiliary
fuel
pressure
is
selected
by
pushing
the
top
of the switch.
The
Hi
auxiliary
fuel
pressure
is
selected
by
pushing
the
bottom
of the switch,
but
this
can
be done
only
after
unlatching the
adjacent
guard.
When
the
Hl
auxiliary
fuel
pump
is
activated,
an
amber
light
near
the
annunciation
panel
is
illuminated for
each
pump.
These
lights dim
whenever the
pump
pressure
reduces
automatically and
manifold
pressure
is
below
approximately
21
inches.
In
case
of
a
failed
engine-driven
fuel
pump,
Hl
auxiliary
fuel
pressure
should
be
selected.
Adequate
pressure
and
fuel
flow
will
be
supplied
for
up
to
approximately 7592
power.
Manual
leaning
to
the
correct
fuel
flow
will
be
required
at
altitudes above
15,000 feet
and
for
engine
speeds
less
than
2300
R PM. An
absolute
pressure
switch
automatically
selects
a
lower
fuel
pres-
sure
when
the throttle
is
reduced
below 21" Hg
manifold
pressure
and
the
Hl
auxiliary
fuel
pump
is
on.
NOTE
Excessive
fuel
pressure
and
very
rich
fuel
air
mixtures will
occur
if
the
Hl
position is
ener-
gized
when
the engine
fuel
injection
system
is
functioning
normally.
Low
auxiliary
fuel
pressure
is available
and
may
be
used
during
normal
engine
operation
both
on
the ground
and
inflight for
vapor
suppression
should
it
be
necessary
as
evidenced
by
unstable
engine
operation
or
fluctu-
ating
fuel
flow indications
during idle
or
at
high
altitudes.
Separate
spring
loaded
OFF
primer
button
switches,
located
adjacent
to
the
starter
switches,
are
used
to
select
HI
auxiliary
fuel
pump
operation for
priming,
regardless
of
other
switch
positions.
These primer
buttons
may
be
used
for both
hot
or
cold engine
starts.
REPORT:
VB-1110
ISSUED:
JANUARY 8, 1981
7-14
REVISED:
AUGUST
17,
1981