S 875-192

 (14)
 Open some of the mask shutoff valves inside the oxygen boxes and bleed the system presure down to zero (00.0) psig.

 S 735-193

 (15)
 Do a visual check that these things occur:

 (a)  
System bleeds down through the masks.

 (b)  
Indicator on the flow control unit moves to OFF.

 (c)  
Close the shutoff valve on the oxygen bottle cart (or portable test cylinder).

 S 415-194
 (16)
 Do the task:  Supernumerary Oxygen Mask Installation (AMM 35-21-06/401).

 S 865-195

 (17)
 Carefully push a 1/4-inch Allen wrench or metal rod through the access hole and lift the plunger on the latch.

 S 015-196

 (18)
 Lift the oxygen box door until it engages the latch and remove the Allen wrench or the metal rod.

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A
747-400
MAINTENANCE MANUAL

 S 085-197
 (19) If the oxygen bottle cart (or portable test cylinder) was used to do the test, remove the test cylinder as follows:
 WARNING:_______LOOSEN THE CONNECTIONS CAREFULLY. THE REMAINING OXYGEN CAN RELEASE WITH A LARGE FORCE. THIS CAN CAUSE INJURY TO PERSONS AND DAMAGE TO THE AIRPLANE AND EQUIPMENT.
 (a)  
Slowly disconnect the oxygen bottle cart (or portable test cylinder) output hose from the coupling assembly at point B (Fig 501).

 (b)  
Install a plug in the opening.

 (c)  
Remove the (0 - 2000 psig) pressure gauge at point C (Fig. 501) and install the plug.

 WARNING: OPEN THE SHUTOFF VALVES ON THE PASSENGER OXYGEN CYLINDERS
_______ SLOWLY. HIGH TEMPERATURES CAN OCCUR WHICH CAN START AN IGNITION WITH THE OXYGEN. THIS CAN CAUSE INJURY TO PERSONS AND DAMAGE TO THE AIRPLANE AND EQUIPMENT.
 (d)  
Open the shutoff valves to each oxygen cylinder:

 (e)  
Slowly turn the shutoff valve until it is fully open. Do not apply more than 25 pound-inches or damage to the valve may occur.

 NOTE: The shutoff valve can be closed by hand which is
____
 equivalent to 25 pound-inches.

 (f)  
Close the shutoff valve one-fourth of a turn.

 (g)  
Install a lockwire on the shutoff valve.

 NOTE: Use the 0.020 inch diameter copper lockwire
____
 (AMM 20-11-28/401).

 (h)  
Do a check at test connections for leaks with leak detection compound.

 (i)  
Rub off the leak detection compound with a clean cotton cloth immediatley after the check.

 S 415-198
 (20)
 Close the access panels to the oxygen cylinder.

 S 865-199

 (21)
 Remove the electrical power if it is not necessary (Ref 24-22-00/201).

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747-400 MAINTENANCE MANUAL
 OXYGEN SYSTEM - INSPECTION/CHECK
________________________________
 1.  General_______
 A.  These tasks are included in this procedure:
 (1)  
Oxygen Cylinder Pressure and Leak Check.

 (2)  
Oxygen Cylinder Security and Condition Check.

 B.  The oxygen cylinders are installed in the forward cargo compartment aft of the cargo door (Fig. 601). Access is through the access panels to the oxygen cylinders.
 TASK 35-21-00-706-011
 2.  Oxygen Cylinder Pressure and Leak Check (Fig. 601)_______________________________________
 A.  Consumable Materials
 (1)  
G00091 Compound - Oxygen System Leak Detection (MIL-L-25567)

 (2)  
G00713 Cloth - Clean, Dry, Lint-free, White, Cotton

 B.  References
 (1)  
AMM 35-00-00/201, Oxygen

 (2)  
　
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