*
High (125F, 51.7C).
EFFECTIVITY
BEJ ALL
The overheat switch is normally closed. It latches open when the tank temperature is approximately 170F (76.7C). The overheat switch can be manually reset (closed) when the tank temperature is less than 120F (48.9C).
The pressure relief valve opens when tank pressure is approximately 140 psig. This valve resets automatically when tank pressure goes below the opening value.
Location
There is a water heater in each lavatory, under the sink.
The overheat switch is under the heater lid.
Indication
The indicator light comes on when both of these conditions occur:
*
The power switch is ON
*
The overheat switch is closed.
It goes out for any of these conditions:
*
The power switch is OFF
*
The overheat switch is open.
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WATER HEATING -INTRODUCTION
Training Information Point
If you use all of the hot water from the tank, the water heater takes approximately 15 minutes to heat the water to the set temperature.
When you drain the potable water system, remove power from the water heaters to prevent an overheat condition.
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WATER HEATING -FUNCTIONAL DESCRIPTION
Functional Description
The printed circuit (PC) card gets temperature selection information from the temperature selection switch. The card
gets water temperature information from the temperature
sensor. It operates the heater elements to maintain the
selected temperature.
The cold water supply connection is on the bottom of the tank. Some of the cold water flows into the tank. It gets heated to the temperature set by the temperature selection switch. Some of the cold water flows through a tube in the tank to the mixing/ bypass device where it mixes with hot water from the tank. The mix of cold and hot water gives a larger volume of warm water than the volume of the tank.
The overheat switch stops the operation of the elements if the water tank temperature is more than 170F (76.7C).
The tank operates with air at the top. The air helps to prevent damage to the tank if the water freezes.
The pressure relief valve opens when tank pressure is approximately 140 psig. This valve resets automatically when tank pressure goes below the opening pressure.
Indication
There is a light on the outside of the heater. It comes on when power is available to the heater. It goes off when any of these conditions occur:
*
Power is not available on the utility bus
*
The power switch is set to OFF
*
The overheat switch is open.
Training Information Point
Remove power from the water heaters when you drain the water system.
Remove the lid to get access to the overheat switch. The water tank temperature must be less than 120F (48.9C) to reset the overheat switch.
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WATER QUANTITY INDICATION -INTRODUCTION
Purpose
The water quantity indication system shows the water quantity in the tanks.
Physical Description
These are the water quantity indication components:
*
Water quantity gauge
*
Water quantity transmitter (2)
*
Water quantity summation unit
*
Water level sensors (part of tanks, not shown).
General Description
The water quantity transmitters send water quantity information to the summation unit. The summation unit sends quantity information to the:
*
Cabin services system (CSS) panels
*
Aft potable water service panel gauge.
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