Hawker 800 XP, Pilot Training Manual

Page: 316 / 504

PRESSURE REGULATOR AND
SHUTOFF VALVE (PRSOV)
From each main air valve (MAV), the air is
ducted via a nonreturn valve (NRV), and then
via a common duct to a pressure regulator and
shutoff valve (PRSOV) unit and a pressure re-
ducing and flow restricting venturi to an air
cycle machine (ACM).
AIR CYCLE MACHINE (ACM)
The air cycle machine (ACM) consists of a
three-wheel cold air unit (CAU), and primary
and secondary heat exchangers which are
cooled by ram air. Excess water is removed by
a water separator at the exit from the ACM. To
enhance the cooling performance, this water
is ejected back into the ram-air flow above
the primary heat exchanger (Figure 11-1).
OVERSPEED PROTECTION
A pressure switch, downstream of the PRSOV,
protects the ACM from overspeed should the
PRSOV fail. The pressure switch operates on
a rising pressure of 40 psi to signal the No. 2
MAV to close.
The No. 1 MAV remains open and the maxi-
mum flow to the CAU is restricted by the ven-
turi in the No. 1 LP bleed duct.
Closure of the No. 2 MAV will be indicated
by the MWS panel annunciator, MAIN AIR
VLV 2, illuminating.
NOTE
The illuminated MAIN AIR VLV 2
annunciator indicates that the posi-
tion of the No. 2 MAV does not agree
with the selection made on the MAIN
AIR VLV 2 switch.
This annunciation is not unique to the over-
speed condition. However, the overpressure
condition also triggers a second indication—
a magnetically latched doll’s eye indicator in
the rear equipment bay. This indication re-
mains triggered until reset by ground-ser-
vicing personnel.
The closure of No. 2 MAV results in a de-
crease in system pressure. To avoid cycling of
the valve, a latch circuit maintains the closed
signal. The system can be reset by selecting
the MAIN AIR VLV 2 switch to CLOSE. This
action causes the MAIN AIR VLV 2 annun-
ciator to go out. If the system pressure has
fallen, the No. 2 MAV will subsequently open
when the switch is selected OPEN.
COLD AIR UNIT (CAU)
The CAU comprises a fan, a compressor and
a turbine mounted on a common shaft.
Bleed air from the venturi enters the ACM via
the primary heat exchanger, which cools this
air to an acceptable level for the CAU. The pri-
mary exchanger is cooled by ram air from an
intake at the base of the fin.
The cooled air from the primary heat exchanger
enters the CAU compressor, which raises its
pressure and temperature before it is cooled
by the secondary heat exchanger. The sec-
ondary heat exchanger uses ram air as the
cooling medium.
From the secondary heat exchanger, the air
is expanded and cooled through the turbine.
The energy extracted in this process is used
to drive the compressor and the fan. The fan
is used to draw cooling air through the ram-
air system.
Revision 1 11-2
FOR TRAINING PURPOSES ONLY
HAWKER 800 XP PILOT TRAINING MANUAL
FlightSafety
international