MASK
STORAGE BOX (DOORS OPEN)
A
HARNESS
INFLATION
EAR

OXYGEN DILUTION CONTROL
PRESS TO
TEST KNOB

EMERGENCY
PRESS
 TO
TEST

REGULATOR
C
Mask/Regulator Figure 3
FLOW BLINKER
REGULATOR
HARNESS INFLATION EAR
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
 8.  Pressure Transducer
___________________
 A.  High pressure indication is received from a pressure transducer which is a component of the cylinder coupling assembly (Fig. 2). The transducer takes system pressure and changes it to a variable electrical signal which controls the oxygen pressure indicator on the aft overhead panel in the control cabin.
 9.  Oxygen Pressure Indicator
_________________________
 A.  An oxygen pressure indicator is installed on the aft overhead panel and supplies high pressure indication for the flight crew oxygen system (Fig. 4). The pressure indicator dial is calibrated to read pressure from 0 to 2000 psi. The indicator contains a unit which takes a voltage output signal from the pressure transducer and changes the signal to a calibrated pressure value that is shown on the dial.
 10. Overboard Vent and Discharge Indicator
______________________________________
 A.  The discharge indicator is a green plastic disk installed in the overboard vent which is adjacent to the crew oxygen cylinder. The indicator will break if the frangible disk in the crew oxygen cylinder breaks. This causes pressure in the overboard vent line to build and this causes the green plastic disk to break. The purpose of the indicator is to permit a visual indication of loss of oxygen through the overboard vent, and prevent entry of foreign objects, insects, etc.
 11. Operation (Fig. 4)
_________
 A.  The crew oxygen system keeps gaseous oxygen under high pressure and supplies oxygen to each crewmember at low pressure. High pressure oxygen flows from the crew oxygen cylinder into the cylinder coupling assembly, then into the attached pressure regulator. The pressure regulator takes an input pressure range of 60 to 1850 psi and reduces it to an output pressure range of 60 to 85 psi. Also connected to the cylinder coupling assembly is a pressure transducer which transmits an electrical signal to control the high pressure indicator on the aft overhead panel.
 B.  A system shutoff valve that is manually operated is installed in the line to control flow to the crew oxygen outlets. The shutoff valve is a slow opening type and is normally open. Operation of the oxygen system is automatic when the cylinder shutoff and system shutoff valves are open and the mask/regulator is removed from the mask storage box. Each individual crew member uses a mask/regulator to control the operation of the system.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
PASS OXYGENOXYGENCREW
NORMAL10
RESET
OXYGEN
TEST
MASK
515 ON
100%
PUSH
28V DC

0 20
OXY PRESS
PASS OXY
BAT. BUS
PSI X 100 ON
C156
a
OXYGEN
SYSTEM IND

P18 CIRCUIT BREAKER PANEL N20 OXYGENT404 PRESSURE TRANSDUCERPRESSURE INDICATOR(FORWARD CARGO COMPARTMENT) P5-14 OXYGEN SYSTEM MODULE(ON AFT OVERHEAD PANEL)
MASK STORAGE BOXA
SYSTEMSHUTOFF VALVE MASK/ MICROPHONE
REGULATOR
(P6 PANEL)
N100%
(CHAPTER 23)
PUSH MASK STORAGE BOX
(CAPTAIN'S STATION)
SEE A
EMERGENCY PRESS
OVERBOARD
TO
TEST
REGULATOR
CABIN
CREW OXYGEN CYLINDER
AIR
(FORWARD CARGO COMPARTMENT)

MASK STORAGE BOXMASK/AND MASK/REGULATORPRESSURE REGULATOR
REGULATOR (FORWARD CARGO COMPARTMENT)
MASK STORAGE BOX
(FIRST OFFICER'S STATION)

SEE A
LEGEND
MASK/REGULATOR
(FIRST OBSERVER'S STATION)
LOW PRESSURE OXYGEN