UFC 3-460-03
21 JANUARY 2003
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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