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2-142
NOMENCLATURE FUNCTION
a OBOGS master switch BACKUP - Deenergizes oxygen concentrator and Process Air Shutoff
Valve. Enables Backup Oxygen.
ON - Applies power to oxygen generator and oxygen monitor.
Opens solenoid valve providing ECS Service Air to Oxygen
Concentrator.
OFF - Removes power from OBOGS and BOS. Process air shutoff
valve closes.
0
VENT AIRFLOW NOT FUNCTIONAL.
0
OXYGEN SUPPLY valve ON- Opens oxygen supply permitting OBOGS or BOS oxygen flow
to crewmember.
OFF - Secures OBOGS and BOS oxygen flow to crewmember.
@
OBOGS caution light Illuminates when OBOGS has failed or OBOGS master switch is in OFF or
BACKUP
@ l33J$XY LOW caution Illuminates when pressure remaining in BOS assembly oxygen cylinder is
below 200 psi.
@ $2; OXY PRESS Indicates pressure remaining in BOS assembly oxygen cylinder.
0
OXYGEN MONITOR Provides functional test of the oxygen monitor, BOS, and OBOGS oontrol
TEST Button systems.
Figure 2-80. Oxygen System Controls and Indicators (Sheet 2 of 2)
2.31.2 BackupOxygenSystem. The BOS consists
of a BOS assembly, BOS controller, B/U OKY
LOW caution light, and a BACKUP OXY PRESS indicator.
This system wsa designed to provide only enough
oxygen for maximum-range descent. In the event of au
OBOGS failure, the aircrew must take immediate action
to conserve backup oxygen.
Switching to the backup system can be accomplished
three ways:
1. Automatically upon monitor detection of an
OBOGS faihue or loss of OBOCX control power
2. Manually via direct selection of BACKUP on the
OBOGS master switch
3. Automatically with total loss of electrical power or
selection of OFF on the OXYGEN system master
switch, when the aimratl is above 10,000 feet MSL.
Backup oxygen cannot be disabled above 10,000 feet
MSL by turning the OXYGEN system master switch
off. Therefore, the individual OXYGEN SUPPLY
valves (Figure 2-80) in both cockpits must be used to
turn off oxygen flow to the personnel regulators.
The BOS assembly consists of an oxygen cylinder,
pressure gauge, pressure regulator, fill pot$ pressure
transducer, low-pressure switch, manual shutoff valve,
and quick disconnect on a pallet&d assembly that is
removable for servicing and maintenance.A 2OOcubicinch,
high-pressurec ylinder containing 500 to 590 liters
of gaseous oxygen at 1,800 to 2,100 psi, respectively,
provides a backup oxygen supply to the OBOGS. The
BOS assembly is located on the right forward side of the
fuselage,ju st below the forward end of the pilot cockpit.
The BOS controller enables flow from the BOS assembly
via a diaphragm valve. This diaphragm valve is
controlled by two solenoid valves and an aneroid valve.
The BOS controller is in the BOS assembly compartment.
Power for automatic operation of the BOS controller
is provided by 28 Vdc essential bus No. 1 via the
OBOGS CONTR circuit breaker. Alternate power is
provided via the BOS CONTRB/u OKY LOW circuit
breaker for automatic activation ofbackup oxygen in the
event of a failure of the OBOGS control relay and when
BACKUP is manually selected.
2-143 ORIGINAL
NAVAIR 0%PUAAD-I
The BAJ OXY LOW caution light is actuatedb y the
BOS assembly low-pressure switch when the BACK UP
OXY PRESS gauge reads less than 200 psi, or when
BOS CONTRiBN OKY LOW power is lost. Figure
2-81 provides backup oxygen breathing time for two
crewmembers for various cabin altitudes based upon
BOS oxygen cylinder pressure.
2.31.3 BOS Pressure Indicator. The BACK UP
OXY PRESS indicator (Figure 2-80), on the right side
of the pilot right knee panel, shows the pressure in the
BOS assembly oxygen cylinder. The indicator will not
function unless the BOS manual shutoff valve on the
BOS assembly is open.
2.31.4 Emergency Oxygen Supply. The 50-
cubic-inch oxygen cylinder in the survival kit of
each ejection seat provides a limited supply of gaseous
oxygen. This oxygencylindercanbemanuallyactivated
in the event of a failure of the OBOGS and depletion of
the backup supply. The cylinder is charged to 1,800 to
2,100 psi and a pressure gauge is visible on the inside
face of the left-thigh support. Flow from the emergency
cylinder is routedt hrough a pressurer educera nd a shuttle
valve, then follows the path of the normal oxygen
system, flowing through the oxygen regulator to the face
mask. The supply of oxygen available in the emergency
cylinder is adequatefo r up to 8 to 10m inutes, depending
upon altitude. The manual actuation handle is a green
ring under the left side of the survival kit cushion.
　
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