28-26-00
ACTUATOR ON THE DEFUELING VALVE ú ú 01 Page 5 ú May 28/99
A
757
MAINTENANCE MANUAL
DEFUEL VALVE
Defueling Schematic Figure 3 (Sheet 2)
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28-26-00
ACTUATOR FOR THE DEFUELING VALVE ú ú 01 Page 6 ú May 28/99
A
757
MAINTENANCE MANUAL
3) The receiving tank pressure fueling shutoff valves must be open.
(b)
If either defueling valve fails closed and cannot be manually opened, opening the crossfeed valve and the second defueling valve will allow defueling.
(c)
The fuel quantity indicating system (AMM 28-41-00/001) allows monitoring of defueling.
(4)
Defuel Valve Operation
(a)
Switches at the fueling station control the defueling valves. The gound handling bus or the hot battery bus provides 28vdc power. Opening the fueling control panel door energizes the fueling panel door relay. Twenty-eight volt dc power passes through the fueling panel door relay to the defuel valve control switch. Opening the switch sends 28vdc power through the control switch to energize the defuel valve control relay. The valve actuator receives 28vdc power through the defuel valve control relay to open the valve.
(b)
The defuel valve control relay relaxes with the fuel valve control switch closed. The relaxed valve control relay provides a direct path for 28vdc power to the valve actuator to close the valve. Closing the fueling panel door before switching the defuel valve CLOSED switch causes the direct flow of 28vdc power to the valve actuator to close the valve.
(5)
Defueling Valve Indication
(a)
A blue DEFUEL VALVE light on the fueling station control panel provides defuel valve position indication. When the defuel valve reaches full open, the limit switch directs 28vdc power to energize the defuel valve indication relay. The DEFUEL VALVE lamp lights when the valve reaches full open. When the defuel valve reaches full closed, the limit switch directs 28vdc power to energize the defuel valve indication relay. The full closed valve shuts off the DEFUEL VALVE light.
B.
Control
(1)
For defueling control refer to AMM 28-26-00/201 defueling.
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