(2)  
The sump drain valves have a valve body with inlet holes, a poppet valve with corresponding holes, and a spring. A valve screen over the valve body inlet holes protects the valve body against contaminants which can clog the poppet valve. Usually held closed by spring force, the holes in the poppet valve do not align with the housing holes. Thus no fuel drains through the sump drain valve. Pushing up on and holding the poppet valve permits the holes in the piston to align with the holes in the valve body and drainage occurs. Pushing up on and holding the drain line fitting of the sump drain valves in the center fuel tank permits drainage. A separate flapper closes over the sump drain valve hole in the wing skin when the sump drain valve is removed from the airplane. This permits removal of the sump drain valves without fuel tank defueling.

 D.
Baffle Rib Check Valve (Fig. 5)

 (1)  
Eleven baffle rib check valves are installed on the baffle rib just inboard of each fueling shutoff valve in the main fuel tank. The check valves prevent fuel flow in the outboard direction but permit fuel flow in the inboard direction. This prevents a low fuel level between the baffle rib and the inboard tank end rib in the main fuel tank. Thus the check valves prevent the boost pump inlets from being uncovered.

 (2)  
Each check valve is a free swinging flow actuated valve. Inboard fuel flow opens the check valves and outboard flow forces the check valves closed.

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A

757 MAINTENANCE MANUAL 
SEE  A 
á  á  SEE B SUMP DRAIN VALVE 
SEE B SUMP DRAIN VALVE SEE B SUMP DRAIN VALVE 
VALVE FLAPPER 
DRAIN LINE CENTER FUEL TANK LOWER SURFACE OF THE SUMP DRAIN VALVE SEE C 

WING-TO-BODY DRAIN LINE FITTING
FAIRING
A
Fuel Sump Drain Valves Figure 4 (Sheet 1)
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A
757
MAINTENANCE MANUAL

FLAPPER
VALVE BODY
VALVE SCREEN
IN THE  O-RING 
FUEL TANK  CAP 
NUT  WASHER  SCREEN VALVE 
SPRING 
O-RING  POPPET VALVE VALVE BODY 
SEE  D 
LOWER SURFACE  O-RING  SPRING 
　
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本文鏈接地址：757 AMM 飛機維護手冊 燃油 CHAPTER 28 - FUEL 1(20)