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assembly and to the switcher solenoid valve assembly. With the solenoid
de-energized, control air passes through the switcher valve and is
transmitted to the pneumatic actuator closing chamber. The force of the
control air pressure acting on the pneumatic actuator piston supplements
the force of the piston spring to maintain the butterfly valve to the closed
position, preventing the flow of air.
As the inlet air pressure rises above the predetermined value, the air
pressure acting on the piston of the metering valve assembly overcomes
the force of the spring, closes the valve, and regulates the pressure to the
switcher solenoid valve assembly.
When the solenoid is energized, control air passes through the switcher
solenoid valve assembly and is transmitted to the pneumatic actuator
opening chamber at a rate determined by the pneumatic actuator chamber
orifice. The pneumatic actuator closing chamber is vented to the
atmosphere through the switcher solenoid valve assembly. As the butterfly
valve opens, downstream air pressure increases and air flows through the
servo assembly to the metering valve assembly, resetting the metering
valve assembly to a desired value for the servo assembly supply pressure.
With air flowing through the unit, the servo assembly acts to regulate the
downstream air pressure at a constant, predetermined value. Downstream
air pressure is sensed in the actuator housing assembly downstream of the
butterfly valve. As downstream air pressure increases, pressure acting on
the servo piston overcomes the force of the piston spring and the piston
lifts the ball valve from the seat, allowing air to bleed from the pneumatic
actuator opening chamber. As control air pressure in the pneumatic
actuator opening chamber increases, the pneumatic actuator piston spring
acts to move the butterfly valve toward the closed position, reducing the
flow of air through the regulator. When downstream pressure decreases,
the servo assembly piston spring moves the piston and seats the ball
valve, stopping the bleed-off of control air pressure from the pneumatic
actuator opening chamber. This cycle modulates the butterfly valve to
control downstream pressure.
Downstream pressure is also sensed through the internal downstream air
pressure sensing port and transmitted to the normally closed overpressure
limiter. In the event of malfunction of the servo assembly, the resulting high
pressure acts on the overpressure limiter piston, overcoming the spring
force and unseating the ball valve. This vents the pneumatic actuator
opening chamber to the atmosphere. When opening chamber pressure
drops, the actuator spring moves the actuator piston, rotating the butterfly
valve toward the closed position and reducing the flow of air through the
unit.
When the butterfly valve rotates more than 6° from the full closed position,
the position indicator switch is actuated, indicating an open butterfly valve.
As the solenoid becomes de-energized, control air passes through the
switcher valve to the pneumatic actuator closing chamber. At the same
time, the pneumatic actuator opening chamber is vented to the atmosphere
through the switcher valve. The force of the control air pressure in the
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-80-00
Page 3
May 31/01
Revision 4
closing chamber and the piston spring then moves the butterfly valve to the
closed position.
3. Controls and Indications:
A. Circuit Breakers (CBs):
The engine starting system is protected by the following CBs:
Circuit Breaker
Name:
CB Panel: Location: Power Source:
ENGINE START P K-6 ESS 28V DC Bus
WARN LTS PWR #3 P F-2 ESS 28V DC Bus
WARN LTS PWR #5 P F-5 ESS 28V DC Bus
WARN LTS PWR #6 P G-1 or G-2 (1) ESS 28V DC Bus
WARN LTS PWR #7 P G-2 or G-3 (1) ESS 28V DC Bus
OVHD ANN LTS PWR
#1 P A-1 or C-1 (1) ESS 28V DC Bus
OVHD ANN LTS PWR
#2 P A-2 or C-2 (1) ESS 28V DC Bus
OVHD ANN LTS PWR
#3 P A-3 or C-3 (1) ESS 28V DC Bus
NOTE(S):
(1) Depending on effectivity.
4. Limitations:
A. Flight Manual Limitations:
(1) Starter Duty Cycle:
Continued use of starter is limited to three (3) crank cycles with a
maximum of thirty (30) seconds per cycle. Delay three (3) minutes
between start attempts. After three (3) cycles, delay use of starter
for at least fifteen (15) minutes.
(2) Starter Re-engagement:
The starter may be re-engaged at HP RPM speeds up to starter
cutout of 42% HP RPM.
(3) Airstart Envelope:
See Figure 3: Airstart Envelope.
OPERATING MANUAL
2A-80-00 PRODUCTION AIRCRAFT SYSTEMS
Page 4
　
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