Aircraft Fuel Systems Overview

Pump Discharge Check Valves

• Prevent reverse flow from the fuel feed manifold back into the fuel tank
• Help prevent this if one fuel pump is stronger than the other

Boost Pump Bypass Suction Port

• Allows both boost pumps to be bypassed
• Enables fuel to be delivered by gravity or engine suction

Fuel Feed Manifolds

• Fuel lines which supply the engines

Cross Feed Manifold

• Interconnects the left and right hand tanks and consumers

Engine Fuel Shut Off Valves

• Enable isolation of fuel flow to an engine
• Also called engine fire shut-off valves or engine low pressure fuel valves

Cross Feed Valves

• Enable feeding the left hand engines from the right hand tanks or vice versa
• Normally closed, ensuring each engine is supplied by its dedicated tank
• Twin-engined aircraft have one, others have more

Sequence Valves

• Pressure relief valves attached to fuel boost pumps
• Reduce output pressure of pumps to ensure fuel from the center tank is used first

Air Release Valves

• Allow air trapped in the fuel line to bleed out under pump pressure
• Prevent air bubbles from being ported to the engine, which could interrupt the fuel supply

Fuel System Components

• Pump discharge check valves prevent reverse flow from the fuel feed manifold back to the fuel tank. This can occur if one fuel pump is stronger than the other.
• Boost pump bypass suction port allows both boost pumps to be bypassed, enabling fuel to be delivered by gravity or engine suction.
• Fuel feed manifolds are fuel lines supplying the engines.
• Crossfeed manifold interconnects the left and right fuel tanks and consumers.
• Engine fuel shut-off valves isolate fuel flow to an engine. These valves are also known as engine fire shut-off valves or engine low pressure fuel valves.
• Crossfeed valves allow fuel to be fed from the right-hand tank to the left-hand engines or vice versa. The valves are normally closed, supplying each engine from its dedicated tank. Twin-engined aircraft have one crossfeed valve, while larger aircraft have more.
• Sequence valves are pressure relief valves attached to some fuel boost pumps. They reduce output pressure from these pumps to ensure fuel from the center tank is used first.
• Air release valves allow air trapped in the fuel line to bleed out under pump pressure. This prevents air bubbles from reaching the engine, which can interrupt the fuel supply.
• Transfer valves in the center tank manage fuel flow between the stabilizer tank and the center tank. Due to the long fuel line routed through the fuselage between the center tank and stabilizer tank, a single line is used for fuel feed and refueling to minimize potential leaks.