____ duct when the sleeve is installed.
The pressure is low in the heat duct. Air leakage at the duct repair joint is permitted.
(f) Tighten the duct support clamps.
S 358-003
(2) Repair a Long Section of the Heat Duct (Procedure 2): NOTE: A long segment is greater than twelve inches (305 mm).
____ A short segment is twelve inches (305 mm) or less.
(a)
Remove the damaged heat duct.
(b)
Make a replacement heat duct from the composite material. NOTE: The length of the replacement heat duct must be
____ approximately the same length as the damaged heat duct.
(c)
Drill the same number of the heat outlet holes in the replacement heat duct that are in the damaged heat duct.
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(d) Make two titanium sleeves which are 6 inches (152 mm) in length.
NOTE:____ The sleeve diameter must be larger than the heat duct diameter.
(e) Install the replacement heat duct and the sleeves as shown in Figure 801.
NOTE:____ Make sure the heat outlet holes are on the top of the duct when the sleeve is installed. The pressure is low in the heat duct. Air leakage at duct repair joint is permitted.
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747-400 MAINTENANCE MANUAL
AFT CARGO COMPARTMENT HEATING SYSTEM - DESCRIPTION AND OPERATION
________________________________________________________________
General (Fig. 1 and 2)
_______
A. The aft cargo heating system supplies hot engine bleed air to the aft and bulk cargo compartments. Engine bleed air is taken from the crossover manifold and carried through a supply manifold to perforated ducts in the cargo compartments.
B. The aft cargo heating system consists of a control valve and override valve installed in series in the supply ducts, plus four temperature control switches. There are two temperature control switches and one overheat switch installed with the bulk cargo temperature sensor in a box located on the left sidewall of the bulk cargo area. An underfloor temperature control switch is installed in the bulk cargo floor area. The underfloor switch is enabled only when aft cargo air conditioning is selected on.
C. The aft and bulk cargo temperature sensors provide compartment temperature indication on EICAS. The cargo zone temperature sensors are treated as an additional zone by the zone temperature controller for BIT and indication (AMM 21-61-00/001).
D. The compartment temperature can be maintained at a low or a high temperature selection with the aft cargo compartment temperature select switch which is located just inside the bulk cargo door. The low and the high temperature selections are as follows:
(1)
Low: 40 degrees F (4 degrees C)
(2)
High: 50 degrees F (10 degrees C)
E. The aft cargo heating system can only be operated when the aft cargo air
conditioning system is not in operation.Aft Cargo Heat Valves
_____________________
A. The control valve and the override valve are identical motor-driven valves located in the right body landing gear wheel well. Limit switches interrupt power at the open and closed extremes of valve travel. External indicators show valve butterfly position.
B. Both valves are powered by 115 volt ac from the 115 vac bus 3 and 28 volt
dc from the 28 vdc bus 1.Temperature Switches
____________________
A. The low and high temperature control switches and the overheat switch are similar units installed on the bulk cargo compartment left sidewall. The switches are installed next to the bulk cargo compartment temperature sensor inside the sensor assembly box. The temperature sensor fan draws compartment air across the temperature switches. A set of contacts within the switch open and close in response to temperature increases or decreases.
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