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757 MAINTENANCE MANUAL
WATER AND DRAIN LINE HEATERS - DESCRIPTION AND OPERATION
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General
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A. Water supply and drain lines are electrically heated to prevent ice formation. System components include heater tapes, blankets, heater tape thermostats, and drain mast heaters. System electrical power comes from the 115-volt ac ground service bus through circuit breakers on the right miscellaneous electrical equipment panel P37. Electrical power for the drain mast heaters also comes from the 28-volt ac ground service bus through a circuit breaker on the APU/External power panel P34.
Component Details (Fig. 1)
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A. Heater Tapes, Blankets
(1) Heater tapes, blankets are wrapped on some water supply and drain lines to prevent freezing. Temperatures of the heaters are controlled by thermostats. Some heaters are equipped with integral thermostats, while others use external thermostats.
B. Heaters Thermostats
(1) Thermostats are used to control the temperatures of the heaters. The thermostats will open when their temperatures exceeds 60 |5°F
(15.5 |3°C), and will reclose when temperatures drops below 45 |5°F
(7.2 | 3°C).
C. Drain Pipe Heater Gaskets
(1) Heater gaskets are installed on the fitting ends of the toilet drain pipes. The heater gaskets are not temperature-controlled by thermostats.
D. Drain Mast Heaters
(1) The forward and aft drain masts are heated to allow for inflight drainage without freezing. Drain mast heater temperature is controlled by an air/ground relay. Low heat is provided on the ground, and high heat is provided inflight.
Operation (Fig. 2)
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A. Functional Description
(1)
There are no control switches for the water and drain line heaters. All heaters are powered when the ground service bus is energized (Ref 24-51-00).
(2)
In flight, all heaters operate as they do on the ground except for the drain masts and one heater tape. The drain masts and heater tape are connected to the high voltage (115-volt AC) tap of the autotransformer through the air/ground relay.
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本文链接地址：757 AMM 飞机维护手册 防冰和排雨 CHAPTER 30 - ICE AND RAIN PROTECTION(174)
