Drain. A drain in the outflow valve static control
line is provided for removal of accumulated moisture.
The drain is located behind the lower sidewall upholstery
access panel in the baggage section of the aft
Flow Control Unit. A flow control unit forward of
the firewall in each nacelle controls bleed air flow and
the mixing of ambient air to make up the total air flow to
the cabin for pressurization, heating, and ventilation.
The bleed air switches located on the overhead control
panel (fig. 2-12) operates an integral electric solenoid
which controls the bleed air to the firewall shutoff
valves. A normally open solenoid operated by the
landing gear safety switch controls the introduction of
ambient air flow to the cabin on takeoff.
The unit receives bleed air from the
engine into an ejector which draws ambient air into the
nozzle of the venturi. The mixed air is then forced into
the bleed air line routed to the cabin.
Bleed air flow is controlled automatically.
When the aircraft is on the ground, circuitry from the
landing gear safety switch prevents ambient air from
entering the flow control unit to provide maximum
The bleed air firewall shutoff valve in the
control unit is a spring loaded, bellows operated valve
that is held in the open position by bleed air pressure.
When the electric solenoid is shut off, or when bleed air
diminishes on engine shutdown (in both cases the
pressure to the firewall, shutoff valve is cut off), the
firewall valve closes.
2-61. OXYGEN SYSTEM.
Description. The oxygen system (fig. 2-20) is
provided primarily as an emergency system; however,
the system may be used to provide supplemental (first
aid) oxygen. Two 64 cubic foot capacity oxygen supply
cylinders charged with aviator's breathing oxygen are
installed in the unpressurized portion of the aircraft
behind the aft pressure bulkhead. The pilot, copilot, and
mission operator positions (2) are equipped with
pressure demand regulators. Also a first aid oxygen
mask is provided in the toilet compartment. Oxygen
system pressure is shown by two gages placarded
OXYGEN SUPPLY PRESSURE, located aft of the
pilot's oxygen regulator
control panel. Two pressure reducers, located in the
unpressurized portion of the aircraft behind the aft
bulkhead, lower the pressure in the system to 400 PSI,
and route oxygen to the regulator control panels. Both
cylinders are interconnected, so refilling can be
accomplished through a single filler valve located on the
aft right side of the fuselage exterior. A pressure gage
is mounted in conjunction with the filler valve, and each
cylinder has a pressure gage. Table 2-4 shows oxygen
flow planning rates and table 2-5 shows oxygen duration
capacities of the system. Figure 2-21 shows oxygen
cylinder capacity percent of rated volume vs pressure
and temperature for an 1800 PSI system.
Regulator control panels.
combustion. Do not smoke while
oxygen is in use.
If any symptoms occur suggestive
immediately set the emergency
pressure control lever to the
Whenever carbon monoxide or
other noxious gas is present or
suspected, set the dilutor control
oxygen until the danger is past.
Each regulator control panel contains a blinkertype flow
indicator, a 500 PSI pressure gage, a red emergency
pressure control lever, a white diluter control lever, and
a green supply control lever.
Oxygen supply pressure gage. The 500
PSI oxygen pressure gages are provided on the oxygen
Gage pressure of over 400 PSI
indicates a malfunction of the
Whenever oxygen is inhaled, a blinker-vane
slides into view within the flow indicator window,
showing that oxygen is being released. When oxygen is
exhaled, the blinker vane vanishes from view.
Change 2 2-47