2. Oxygen Cylinders (Fig. 2 and 3)
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A. Oxygen storage cylinders supply oxygen to the oxygen system. The cylinders are installed in the forward cargo compartment sidewall. Each cylinder has a quantity of oxygen equivalent to 114 cubic feet at 760 mm Hg absolute and 70°F when filled to 1850 psig. Space is provided for additional cylinders.
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B. The cylinder assemblies each include a slow opening shutoff valve, a pressure gage, and a safety outlet device which bursts before pressure reaches a value that could damage the cylinder, tubing, or components. The safety outlet devices are manifolded to a line which runs to an overboard discharge port in the airplane skin. The overboard discharge port incorporates an indicator (a plastic disc) which normally prevents dirt, grease, etc., from entering the discharge line, but which ruptures at a pressure of 500 psig to allow oxygen to discharge overboard. The overboard discharge line serves both the supernumerary and crew systems.
3. Flow Control Unit (Fig. 2)
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A. The flow control unit is installed in the supernumerary oxygen system to supply a continuous low pressure flow of oxygen to each supernumerary passenger. The units are found in the sidewall of the forward cargo compartment and connected in the oxygen distribution line.
B. Electropneumatic Flow Control Unit
(1) The M101 electropneumatic flow control unit has a pressure reducer, pressure switch, surge chamber, and an actuation valve. The actuation valve may be operated by an automatic aneroid mechanism or by a solenoid-controlled actuator which is activated by a switch on the P5 Pilot's Overhead Panel. To return the system to normal after the control unit has been actuated either automatically or electrically, the actuation valve must be reset (Fig. 3). The units cannot be reset when cabin pressure is equivalent to a 12,000-foot altitude or higher.
(a) A pressure switch, in the low pressure side of the unit, supplies a ground for the R36 decompression relay and signals the EICAS to show the advisory message, SUPRNMRY OXYGEN ON, which shows that the low pressure oxygen distribution system is pressurized and the oxygen system is actuated.
C. Flow Control Unit Resetting
(1) The flow control unit is turned "OFF" when you move the SUPRNMRY OXYGEN switch on the P5 Pilot's overhead panel to the RESET position. This reset is done by a solenoid/reset lever mechanism which turns the flow conrol unit off. This simultanioulsy moves the flow control unit indicator to the "OFF" position. The flow control unit must be reset following actuation to prepare the system for future use.
4. Low Pressure Distribution System (Fig. 1)
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A. The flexible tubing attaches to connections along each manifold and delivers oxygen to the oxygen boxes. The distribution system is vented to the cabin ambient pressure through an automatic vent valve which closes when the oxygen system is actuated. Bleed relief valves are installed at various locations along the low pressure distribution lines to relieve pressure exceeding 27 |1.5 psig.
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5. Automatic Vent Valve (Fig. 2)
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A. The automatic vent valve is used in the normally unpressurized low pressure distribution system to vent oxygen from the flow control units in event of possible leakage. This leakage must be bled from the system to prevent system pressure buildup and subsequent actuation of the service unit latches and dropping of the masks. When the oxygen system is actuated, the vent valve automatically closes when manifold pressure exceeds 1 psig to prevent loss of oxygen.
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