B. The mask/regulator contains an oxygen mask with a microphone, an
inflatable harness, and a diluter demand regulator.
C. The mask harness is inflated with oxygen by pressing the harness inflation ears on the diluter demand regulator. The harness inflates rapidly to a large, round and rigid shape; allowing the user to rapidly don the mask/regulator. Releasing the inflation ears deflates the harness and allows it to conform to head shape.
D. The diluter demand regulator has three manual controls - harness inflation ears, an oxygen dilution control, and a PRESS TO TEST knob.
(1)
The harness inflation ears are used to inflate and deflate the mask harness.
(2)
The oxygen dilution control is used to select a flow of 100 percent oxygen.
(3)
The PRESS TO TEST knob has two functions. One, rotating the knob provides a positive flow of oxygen under pressure. The oxygen dilution control must be at 100 percent for this to occur. Two, depressing the knob allows the regulator to be tested when the mask regulator is in the mask stowage box.
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35-11-00
ALL ú ú 10 Page 9 ú Oct 18/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
11. Operation (Fig. 6)
_________
A. Functional Description
(1)
The crew oxygen system stores gaseous oxygen under high pressure and supplies oxygen to each crew member at low pressure.
(a)
High pressure oxygen (1850 psig) flows from a crew oxygen cylinder through the cylinder coupling assembly, and through the pressure reducer. The pressure reducer reduces the input high pressure (600 to 1850 psig) to an output intermediate pressure of 600 to 680 psig.
(b)
Connecting to the cylinder coupling assembly is the pressure transducer which transmits an electrical signal to the voltage averaging unit. The output of the voltage averaging unit is then fed to EICAS.
(c)
The medium range pressure plumbing consists of a line from the pressure reducer outlet to the pressure regulator in the flight deck.
(d)
The pressure regulator reduces inlet pressure to an outlet pressure ranging from 60 to 85 psig. The pressure regulator relief valve opens when the outlet pressure exceeds 100 to 110 psig to protect the system components downstream.
(e)
Oxygen flows from the pressure regulator to each mask stowage box. Operation of the system is automatic when the cylinder shutoff valves are open and the mask/regulator is removed from the stowage box. Control is by the individual mask/regulator.
(2)
Normal Mode
(a)
When the mask/regulator is stowed and lids are closed, the shutoff valve is kept in closed position by means of the sliding control. Consequently, neither spillage nor flow through the regulator in any condition is permitted in the stowed position.
(b)
When the mask/regulator is taken out of the mask stowage box, the subsequent opening of lids releases the shutoff valve piston and allows the valve to open.
(c)
After the mask/regulator has been taken out of the mask stowage box, the lids can be closed without shutting off the pressure supply to the regulator. When closing the left-side lid, the inner part of the sliding control rotates and shows the white flag marked OXY-ON. During mask/regulator restowing, it is necessary to pull on the sliding control in order to reset the ON-OFF position. The white flag creates a protrusion which prevents restowing of mask/regulator with the shutoff valve in the ON position.
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