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Figure 5.8. Self-Priming Centrifugal Defueling Pump.
Figure 5.9. Centrifugal Priming Pump Operation.
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5.12. Remote Controls (Electrical and Magnetic). Remote control of fueling, defueling, and
emergency stop is performed by a three-element magnetic control KISS switch located near each
hydrant pit. A magnet controls each of the three functions. Placing the horseshoe magnet on either the
refuel or defuel KISS switch causes the appropriate pump to be energized. Usually a lanyard is attached
to the magnet for quick removal. A magnet in the cover over the emergency stop switch holds the
switch closed. By lifting the cover, the switch is deactivated and the system shuts down. Spring-loaded
covers over the refuel and defuel switches may be removed.
5.13. Hydrant Adapter and Liquid Control Valve (352AF).
5.13.1. The 352AF (Figure 5.10) provides a quick pressure-tight connection with the MH-2 hose
cart’s 351AF moosehead. The 352AF has a float assembly that controls the level of fuel maintained
in the piping at the end of defueling. The float keeps air from entering the system.
Figure 5.10. Hydrant Adapter (352AF).
5.13.2. During fueling operations, the 352AF float assembly is lifted from its seat as the float
chamber fills with fuel to open the valve. At the end of the defueling operation, the float chamber
drains and the float drops to close the valve, preventing air from entering the system.
5.13.3. A replacement poppet kit is available for the Cla-Val 352AF hydrant adapter. This kit must
be installed on all adapters to preclude a sticking problem encountered with the original poppet. The
poppet face will be stamped as MOD-1 if the kit is installed.
5.13.4. The API 364AF-2 hydrant adapter and its mating moosehead are industry-standard
replacements for the hydrant adapter of the 352AF and the 351AF moosehead. Replacing the older
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adapters must be a joint economic decision between the BCE and refueling maintenance as hydrants
and MH2 hose carts must be modified at the same time.
5.14. Hydrant Hose Cart. The MH2 hose cart contains an F/S and meter. Maintenance of hose carts is
the responsibility of refueling maintenance.
5.15. High Level Shut-Off (HLSO). The 124AF has been upgraded to the 129AF (Figure 5.11) by
installing an ejector and ball float assembly. The setting is the same as for a Type I system (279
millimeters [11 inches] from the top of the tank). See Chapter 10 for maintenance frequency.
Figure 5.11. HLSO Valve (129AF).
5.16. Type II Modified (Rapid Flow). The Rapid Flow modification was done at some bases to
increase defuel rates from 757 to 1135 liters per minute (200 to 300 gallons per minute) to speed the
turnaround of KC-135s and other large aircraft. A pump on the aircraft flows fuel from the aircraft
through the LCP and into the designated defuel tank. Hydraulic power for the pump comes from
operating one engine at idling speed. The defueling pump in the LCP is only used to evacuate the hose
cart after the aircraft pump is de-energized.
5.16.1. Combination Dual Rate-of-Flow Control, Solenoid Shutoff and Check Valve (41AF-10).
This valve (Figure 5.12) operates the same as the 41AF, with the addition of a solenoid for remote-
control operations. All settings and functions are the same as the 41AF.
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Figure 5.12. Combination Dual Rate-of-Flow Control Valve and Solenoid Valve (41AF-10).
5.16.2. Combination Dual Pressure Relief, Solenoid Shutoff and Check Valve (51AF-4):
5.16.2.1. General. The dual pressure relief valve (Figure 5.13) is installed in the modified hydrant
lateral control pit downstream of the refueling control valve between the hydrant lateral pipe line
and the defueling line (bypass piping around defuel pump, as shown in Figure 5.1). This relief
valve performs two functions: relieves excess pressure in the hydrant lateral piping caused by
quick-closing valves during the refueling operation; and maintains a minimum pressure of
5 psi on the hydrant lateral piping when the refueling pumps are not in operation. This valve also
has a CV flow control to slowly close the valve during rapid defueling operations.
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Figure 5.13. Dual Pressure Relief, Solenoid Shutoff, and Check Valve (51AF-4).
5.16.2.2. Operation. During rapid defueling operations, pressure supplied by the aircraft pumps
will open the low-pressure side of the 51AF-4 and provide thermal relief for the hydrant lateral
piping. When the refueling pumps are started the solenoid is energized, locking out the low-
pressure relief control and putting the valve under the command of the high-pressure relief control.
5.16.2.3. Pressure Setting:
5.16.2.3.1. When the refueling pumps are in operation, set the high-pressure CRL at
5 psi above the 90AF-8 CRL set point.
5.16.2.3.2. When the refueling pumps are stopped, set the low-pressure CRL at 5 psi.
5.16.2.3.3. Adjust the CV flow control closing speed to provide a smooth, pulsation-free
operation.
5.16.3. Recommended Setting Procedure for the Combination Dual Pressure Relief, Solenoid
Shutoff, and Check Valve (51AF-4).
5.16.3.1. Low-Pressure CRL Setting:
5.16.3.1.1. Place the magnet on the refueling KISS switch to pressurize the system (no hose
cart is need for this procedure).
5.16.3.1.2. When system pressure has built up and the refueling control valve (90AF-8) has
closed, remove the magnet from the refueling KISS switch.
5.16.3.1.3. The 51AF-4 should open and the system pressure should drop.
5.16.3.1.4. When the 51AF-4 closes, note the pressure gauge reading.
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