(a)
Remove water from the fuel tank
(b)
Do a check for fuel contamination
(c)
Do a check for ice accumulation
(d)
Collect a fuel sample for microbial growth detection (AMM 28-11-00/701)
(e)
Do a check of the water scavenge system
(f)
Drain fuel to defuel the tank (AMM 28-26-00/201)
(g)
Drain fuel from the surge tanks to reset the overfill protection system
(3)
It is recommended to drain the fuel sumps regularly.
D. Water In the Fuel Tank
(1)
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.
(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 the rate of approximately one foot (30 cm) per hour.
(3)
Drain the tank sumps sufficiently to make sure you remove all of the water.
(4)
A large quantity of water drained from one fuel tank before refueling can show a blocked water scavenge ejector pump. To examine the water scavenge system,refer to (AMM 28-22-13/401).
(5)
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.
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(6) 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.
E. Fuel Contamination
(1)
You can visually inspect the fuel collected from the sump drain for contamination.
(2)
Fuel with no water, ice, or contamination, is clear and bright and very transparent. The words "clear and bright" mean that you cannot see undissolved water, sediment, or suspended material when you examine the fuel in a clear glasscontainer. If the fuel is free of these types of contamination, it is clear and bright.
(3)
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.
(4)
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 growth (AMM 28-11-00/701).
(5)
If the fuel has a pink or a red color, refer to 747-SL-28-081A to do an inspection for red dye contamination.
F. Cold Weather Operations
(1)
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 degrees Celsius (32 degrees Fahrenheit), then you may have to supply heat before you can drain the sumps.
(2)
Cold weather can also cause the drain valve to stay open or damage the O-ring when you push the poppet valve open. Cold weather can also prevent the correct re-seating of the primary or secondary poppet valve after you drain the fuel.
(3)
You can also use an approved anti-ice additive if the fuel specification allows it. For example, you can add Phillips PFA 56MB in a maximum concentration of 0.1% by volume.
(4)
For cold weather maintenance, refer to AMM 12-33-01/301.
G. Sump Drain Valves Installed in the Surge Tank
(1)
The sump drain valves in the surge tanks are installed to do a check for fuel in the surge tank before you remove the access door for entry.
(2)
Fuel in the surge tank will drain into the main fuel tanks through the drain check valve in each surge tank. To quickly drain the wing surge tanks and reset the overfill protection system, do this task: Drain the Wing Surge Tank with the Surge Tank Drain Fitting.
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