King Air C90GTi, Pilot Training Manual

Page: 210 / 557

ENGINE BLEED AIR
PNEUMATIC SYSTEM
The pneumatic system in Beechcraft King
Airs provides support for several operations
on the air plane. These operations include
surf ace deice, r udder boost, escape hatch
seal, and the door seal. Pneumatic pressure
is used to create a vacuum source for the air-
driven gyros, pressurization control, and de-
flation of the deice boots.
High-pressure bleed air from each engine
compressor section, regulated at 18 psi, sup-
plies pressure for the surface deice system,
r udder boost, escape hatch and door seals,
and vacuum source (Figure 9-1). Vacuum
for the flight instr uments is derived from a
bleed-air ejector. One engine can supply suf-
f icient bleed air for all these systems.
D u r i n g s i n g l e - e n g i n e o p e r a t i o n , a c h e c k
valve in the bleed air line from each engine
prevents flow back through the line on the
s i d e o f t h e i n o p e r a t ive e n g i n e . A s u c t i o n
gage calibrated in inches of mercur y, on the
copilot’s subpanel, indicates instrument vac-
uum (GYRO SUCTION). To the right of the
suction gage is a PNEUMATIC PRESSURE
gage, calibrated in pounds per square inch,
which indicates the air pressure available.
PNEUMATIC AIR SOURCE
Bleed air at a maximum rate of 90 to 120
psi pressure is obtained from both engines,
a n d f l ow s t h r o u g h p n e u m a t i c l i n e s t o a
common manifold in the fuselage. Check
valves prevent reverse flow during single
engine operation.
Downstream from the manifold, the bleed
air passes through an 18 psi regulator which
incor porates a relief valve set to operate at
21 psi in case of regulator failure. This reg-
ulated bleed air is used to supply pneumatic
pressure to inflate the surface deicers, escape
hatch and door seals, and to provide flow
and pressure for the vacuum ejector.
Bleed air is extracted from the P
3
tap of the
engine at a temperature of approximately
4 5 0 ° F. I t i s c o o l e d t o a p p r ox i m a t e ly 7 0 °
above ambient temperature at the manifold
in the fuselage due to heat transfer in the
pneumatic plumbing.
O r d i n a r i ly, t h e p r e s s u r e r eg u l a t o r va l ve ,
which is under the right seat deck immedi-
ately forward of the main spar, will provide
18 +1 psi with the engine r unning at 70 to
8 0 % N
1
. T h e P N E U M AT I C P R E S S U R E
gage on the copilot’s right subpanel is pro-
vided to allow monitoring of the system pres-
sure (Figure 9-2).
VACUUM AIR SOURCE
Vacuum is obtained from the vacuum ejec-
tor. The ejector is capable of supplying from
15 inches Hg vacuum at sea level, to 6 inches
Hg vacuum at 31,000 feet. The ejector sup-
plies vacuum for the pressurization control
system at a regulated 4.3 to 5.9 inches Hg
through a regulator valve.
The vacuum regulator is in the nose com-
partment on the left side of the pressure bulk-
head. The valve is protected by a foam f ilter.
With one engine r unning at 70 to 80% N
1
,
the vacuum gage on the copilot’s right sub-
panel nor mally should read approximately
5.9 +0/–0.2 inches Hg.
KING AIR C90GTi/C90GTx PILOT TRAINING MANUAL
9-3
FOR TRAINING PURPOSES ONLY
9
PNEUMA
TICS
Figure 9-2. Pneumatic Pressure Gage