6. Fuel Crossfeed Valve
A. A fuel crossfeed valve provides the means of directing fuel to both engines. The valve is mounted on the wing front spar in the left wing. This valve is the same design as the engine fuel shutoff valve (see par. 2 and Fig. 2).
7. Boost Pump Bypass Valve (Airplanes With Valve Lock Actuating Arm)
A. A boost pump bypass valve allows the engines to draw fuel from a tank by suction in case of complete boost pump failure in that tank (Fig. 1). The valve also allows defueling the tanks by suction through the manually operated defueling valve. The valve consists of an L-shaped housing having a pressure inlet port, a suction inlet port, and an outlet port. Both inlet ports contain a normally closed flapper type check valve. A screen on the suction port prevents foreign material from entering the feed system lines. The valve in the suction port may be manually locked in the closed position, from outside the fuel tank, by a mechanism that protrudes through the wing lower surface (Fig. 3).
B. With boost pump pressure applied, the check valve in the pressure inlet port will be open and the check valve in the suction port will be closed, allowing the fuel to be pumped to the engine. With suction applied to the outlet port, the valve in the suction port will be open and the valve in the pressure inlet port will be closed, allowing the engine to draw fuel from the tank.
5C8 Boost Pump Bypass Valve with Valve Lock Actuating Arm
Feb 20/86 Figure 3 28-22-0
Page 7
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
8. Boost Pump Bypass Valve (ALL EXCEPT Airplanes With Valve Lock Actuating Arm)
A. A boost pump bypass valve allows the engines to draw fuel from tank No. 1 or 2 by suction in case of complete boost pump failure in that tank. The valve also allows defueling the tanks by suction through the manually-operated defueling valve. The valve consists of a suction inlet port with a normally closed flapper-type check valve. A screen on the suction port prevents foreign material from entering the feed system lines.
B. With boost pump pressure applied, the check valve in the suction port will be closed, allowing the fuel to be pumped to the engine. With suction applied, the valve in the suction port will be open, allowing the engine to draw fuel from the tank.
9. APU Fuel Shutoff Valve
A. The APU fuel shutoff valve is mounted on the left wing rear spar and controls delivery of fuel from tank No. 1 to the APU (Fig. 1). The valve is an electric motor-driven rotary gate valve with a manual override handle. The manual override handle provides a visual check of the valve position and a manual method of positioning the valve when the electric motor is not energized. To limit pressure buildup in the fuel lines, the valve housing incorporates a thermal relief valve. The valve is operated by 28-volt dc power and is controlled by the APU master switch.
10. Fuel Lines and Couplings
A. The lines that transfer fuel from the tanks to the engine are fabricated from seamless aluminum alloy tubing, and are connected to the various fuel system components by standard unions, couplings or flanges. The lines in the wings are mainly located inside the fuel tank boundaries.
B. The APU fuel line from the point at which line leaves wing center cell to the bulkhead connection on the APU shroud is mainly a flexible hose enclosed in a metal fuel line shroud. The fuel line continues from the APU shroud to the APU fuel control but is not separately shrouded for this distance.
569
28-22-0 Page 8 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. May 01/01
F74537
510 Boost Pump Circuit
May 15/68 Figure 4 28-22-0
Page 9
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
EFFECTIVITY
AIRPLANES WITH BOOST PUMP BYPASS VALVES WITH VALVE LOCK ACTUATING ARMS
F95100
Engine Fuel Feed System Flow Diagram 5C8
28-22-0 Figure 5 (Sheet 1) Jun 20/85
Page 10
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
EFFECTIVITY
ALL EXCEPT AIRPLANES WITH BOOST PUMP BYPASS VALVES WITH VALVE LOCK ACTUATING ARMS
5C1 Engine Fuel Feed System Flow Diagram
Jun 20/86 Figure 5 (Sheet 2) 28-22-0
Page 10A/10B
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
11. Operation
A. The engine fuel shutoff and fuel crossfeed manifold valves are operated by 28-volt dc motors receiving their power from circuit breakers on circuit breaker panel P6. The fuel boost pumps are driven by 115-volt three-phase electric motors which obtain their ac power from circuit breakers on circuit breaker panel P6 (Fig. 4). Pumps in the same tank do not receive their power from the same bus. The pump power sources have been arranged so loss of power to one bus will only affect one pump for each tank.
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