UFC 3-460-03
21 JANUARY 2003
6.6.1.2.11. With two, three, or four pumps running, if the return venturi DPT senses between
151 and 2649 liters per minute (40 and 700 gallons per minute), the activated pumps will
continue to run without calling on an additional pump.
6.6.1.2.12. With the lead, second, third, and fourth pumps running, if the return venturi DPT
senses over 2649 liters per minute (700 gallons per minute) for 15 consecutive seconds, the
microprocessor will call off pumps two, three, and four in the reverse order after each
15-second interval.
6.6.1.2.13. With only the lead pump running (2271 liters per minute [600 gallons per minute]),
if the return venturi DPT senses over 2120 liters per minute (560 gallons per minute) for 60
consecutive seconds, the system will initiate shutdown.
6.6.1.2.14. During shutdown, the solenoid on the BPCV will D/C the valve and cause the
hydrant loop pressure to rise.
6.6.1.2.15. When the loop pressure reaches 175 psi, three things happen:
6.6.1.2.15.1. The microprocessor calls off the lead pump.
6.6.1.2.15.2. Solenoid A on the D/FV will E/E the valve to bleed the system pressure to
80 psi.
6.6.1.2.15.3. PCV solenoid will D/E the valve to bleed the pressure to 75 psi.
6.6.1.2.16. Now the system is back to the automatic mode/idle condition.
6.6.1.3. Defueling Condition. To begin an aircraft defueling operation, an operator connects the
HSV between the aircraft and HCV API adapter. The HSV has an on-board defuel pump capable
of pumping 1135 liters per minute (300 gallons per minute) at 165 psi. When the operator starts
the defuel pump, the following sequence will occur:
6.6.1.3.1. If pumps are running (PCV and D/FV are E/C), the fuel being removed from the
aircraft will either go to any other aircraft connected to the system or the fuel will modulate the
BPCV open between 100 and 130 psi to return fuel to the operating tank.
6.6.1.3.2. If pumps are not running (PCV and D/FV are D/E), the fuel being removed from the
aircraft will modulate open both the PCV at 75 psi and the D/FV at 80 psi to allow fuel to flow
to the operating tank.
6.6.1.3.3. If no refueling operations are planned, the system can be placed in flush mode to
expedite defueling. NOTE: Ensure refueling pumps are not started when the system is placed
in flush mode.
6.6.2. Flush Mode. Although fuel entering the hydrant system is filtered at least twice, contaminants
and water can still enter the hydrant loop. Some contaminants drop out in the system and tend to
accumulate in low points. To keep a pipeline clean, fuel must flow at a minimum velocity of
1.8 meters (6 feet) per second. Calculations show that a 0.3-meter (12-inch) line flowing at
2271 liters per minute (600 gallons per minute) will have a velocity of about 0.5 meter (1.7 feet) per
second. At 9084 liters per minute (2400 gallons per minute), the velocity of 2 meters (6.7 feet) per
second is just over the minimum velocity of 1.8 meters (6 feet) per second. To completely flush the
system, at least twice the loop capacity must be pumped through the loop at maximum velocity. For
example, if the Type III loop can hold 75,708 liters (20,000 gallons) of fuel, 151,416 liters (40,000
gallons) must be pumped through the system. If the largest part of the loop is a 0.3-meter diameter
pipe, and the flow rate is 9084 liters per minute (2400 gallons per minute), the system would be
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