500 
12-11-04 Page 306  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  May 01/03 

500 
May 01/03  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  12-11-04 Page 307 

FUEL TANK SUMPING - SERVICING
1.  General
A.  This procedure has this task:
(1)  Drain the tank sump for each tank.
B.  You must not let the fuel tanks collect too much water.  Do the procedure to drain the sump drain valves for each tank regularly.
C.  Obey all of the safety precautions in the task: Precautions and Limits for the Refuel Operation (AMM 12-11-01/301).
2.  Fuel Tank Sumping (Fig. 301)
A.  General
(1)  
The fuel tank sumps must be drained regularly for the removal of water from the fuel tanks.  Each fuel tank sump has a drain valve that drains the water from the fuel tank.  Water in the fuel tank comes from condensation or from fuel that is uploaded during a refuel operation.  Removal of water will help minimize microbial growth that exists at the fuel/water interface.  Microbial growth can cause fuel system degradation including clogged engine filters, fuel quantity indication problems, and eventually structural corrosion.  You can also use the fuel tank sump to do the subsequent:

(a)  
Do a check for fuel contamination

(b)  
Do a check for ice accumulation

(c)  
Collect a fuel sample for microbial contamination (AMM 28-11-0/201)

(d)  
Drain fuel to defuel the tank (AMM 28-23-0/201).

(2)  
During refueling or airplane operations, water mixes in the fuel.  Schedule the task to drain the fuel tank after sufficient time has elapsed to let the water settle to the bottom of the tanks. Water sinks in fuel at a rate of approximately one foot (30 cm) per hour.

(3)  
Look at each fuel sample for water, for ice, or for contamination. Water in a fuel sample usually shows as a layer below the fuel, or as small bubbles in the fuel.  Ice crystals usually appear as cloudiness or haziness and makes the fuel less transparent.  To help you see the water in the fuel, you can add one or two drops of food coloring (water soluble) into the container of fuel.  Any water in the fuel will be shown by a color. You can put the food coloring into the container before you drain the fuel sump.

(4)  
Fuel with no water, ice or contamination is clear and bright and very transparent. The words "clear and bright" mean than you cannot see undissolved water, sediment, or suspended material when you examine fuel in a clear glass container.  If the fuel is free of these types of contamination, it is clear and bright.

NOTE:  Jet-A fuel can have a range of colors from yellow (straw) color to no color.  The words "clear and bright" is not a reference to the color of the fuel.  Yellow fuel or fuel that has no color can be "clear and bright" as specified above.

(5)  
If the water in the fuel has a foul odor or a brown color, then it is possible there is microbial contamination.  Refer to the check for microbial contamination (AMM 28-11-0/201).

(6)  
If the fuel has a pink or a red color, do an inspection for red dye contamination 
 (AMM 28-10-0/701).

(7)  
In cold weather, the water can freeze on the inside and outside of the fuel tanks.  The frozen water can prevent the sump drain valve from opening.  If the ambient temperature is less than 0° Celsius (32° Fahrenheit), then you may have to supply heat before you can drain the sumps.

(a)  Drain the sumps within one hour after remove the airplane from the hanger if the ambient temperature is less than 0° Celsius (32° Fahrenheit).

(8)  
Cold weather can also cause the drain valve to stay open or damage the O-ring when you push the poppet open.  Cold weather can also prevent the correct re-seating of the primary or secondary poppet valve after you drain the fuel.

(9)  
You can also use an approved anti-ice additive if the fuel specification permits it.  For example, you can add Phillips PFA 56MB in a maximum concentration of 0.1% by volume.

(10)
For cold weather maintenance, refer to AMM 12-50-0/201.

(11)
AIRPLANES WITHOUT AN INTEGRAL CENTER FUEL TANK; The wing center cavity drain system is installed with a drain valve to let water be drained from the low point of the system.  If fuel is present in the drained fluid, it shows there is a leak in the fuel tanks, bladder cells or APU fuel line or fittings within the APU fuel line shroud.

(12)
AIRPLANES WITH AN INTEGRAL CENTER FUEL TANK; A center cavity drain system is not used, but drain lines and a drain valve are installed to drain condensation or fuel leakage from the APU fuel line shroud and, if installed, the auxiliary tank shroud and cavity drain system.  If there is fuel in the drained fluid, it shows there is leak:
　
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