King Air C90GTi, Pilot Training Manual

Page: 275 / 557

When the BLEED AIR switches on copilot’s
left subpanel are OPEN a bleed-air shutoff
electric solenoid valve on each flow control
u n i t o p e n s t o a l l ow t h e bl e e d a i r i n t o t h e
unit. The flow control unit will then adjust
the flow of bleed air mixed with ambient air
into the pressure vessel. Ambient air is al-
lowed to enter the flow control unit through
a n o r m a l ly - o p e n m o d u l a t i n g va l v e , a n d
ser ves to add air mass and some cooling to
the bleed air flow.
The ambient air valve, associated with the
t e m p e r a t u r e s e n s i n g d ev i c e , i s a l s o c o n -
trolled by the left landing gear safety switch.
When the aircraft is on the ground, the valve
is directed to shut off the ambient air source
from the flow control valve. The exclusion
of ambient air allows faster cabin war m-up
during cold weather operation.
After takeoff, the landing gear safety switch
signals the ambient air modulating valves
to open. They do so sequentially to prevent
the simultaneous opening of the modulat-
ing valves and a sudden pressure surge into
the cabin.
T h e p n e u m o s t a t ( p n e u m a t i c t h e r m o s t a t )
provides temperature input to the flow con-
trol unit, which modulates the amount of
ambient air entering the flow unit for blend-
ing. War mer outside air opens the modu-
lating valve and allows more ambient air in
for blending. Cold air closes the valve until
i t c l o s e s c o m p l e t e ly a t a p r e s e t t e m p e r a -
t u r e . A t t h i s p o i n t , bl e e d a i r w i l l b e p r o -
viding all air for pressurization. A check
valve prevents air from leaking out the am-
bient air input.
An aneroid near the bleed air ejector flow
control actuator influences the amount of
bleed air entering the flow control unit. The
aneroid provides altitude sensing infor ma-
tion to the flow control unit, and combined
w i t h t h e p n e u m o s t a t , p r ov i d e s a c c u r a t e
bleed-air input into the pressure vessel.
The quantity of bleed-air flow into the pres-
sure vessel is influenced directly by ambi-
ent temperature and ambient pressure.
KING AIR C90GTi/C90GTx PILOT TRAINING MANUAL
12-12
FOR TRAINING PURPOSES ONLY
12
PRESSURIZA
TION