The scavenge system removes fuel from the low points of the center and feed tanks. This reduces the amount of unusable fuel.

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There is one scavenge ejector pump and it is installed in the center tank. It gets its motive flow input from the left and right center transfer pumps.

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The center tank ejector pumps scavenge fuel that cannot be transferred by the center transfer pump. The forward and aft AC boost pumps supply motive flow to the center tank ejector pumps. The motive flow through the center tank ejector pumps causes suction at the inlets of the center tank ejector pumps. The center tank ejector pumps transfer the scavenged fuel into the feed tank. Internal check-valves, located at the inlets of the center tank ejector pumps, prevent fuel back flow into the center tank. The center tank ejector pumps are installed on strainers, adjacent to the center transfer pumps. 

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The feed tank ejector pumps scavenge fuel in the feed tanks. The DC auxiliary pumps supply motive flow to the feed tank ejector pumps. The motive flow through the feed tank ejector pumps causes suction at the inlets of the feed tank ejector pumps. The feed tank ejector pumps transfer the scavenged fuel into the collector boxes. The feed tank ejector pumps are installed on strainers in the inboard section of the feed tanks.

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The center transfer/scavenge check-valves are spring-loaded, poppet-type valves. The center transfer/scavenge check-valves are installed in the center tank-fuel scavenge-lines at LBL47.61 and RBL47.61. The center transfer/scavenge check-valves control the flow of fuel to the feed tank. The center transfer/scavenge check-valves prevent the flow of fuel from the center tank ejector pumps in the opposite direction.

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The center motive flow check-valves are spring-loaded, swing-type valves. The center motive flow check-valves are installed in the center tank-fuel scavenge-lines near LBL47.61 and RBL47.61. The center motive flow check-valves control the flow of fuel to the center tank ejector pump. The center motive flow check-valves prevent the flow of fuel from the AC boost pumps in the opposite direction.

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The center transfer pump check-valves are spring-loaded, poppet-type valves. The center transfer pump check-valves are installed in the center tank-fuel scavenge-lines near LBL27.00 and RBL27.00. The center transfer pump check-valves control the flow of fuel to the feed tanks. The center transfer pump check-valves prevent the flow of fuel from the center transfer pumps in the opposite direction.

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Fuel Scavenge System

The purpose of the fuel scavenge system is to reduce the amount of unusable fuel in the wing and center tanks. The fuel ejectors are used to recover an additional (approximately) 130 pounds of previously unusable fuel from these tanks.

The fuel scavenge system incorporates two subsystems:

Wing Tank Scavenge System

The wing tank scavenge system ejectors receive motive flow when the DC AUX PUMPs are in operation (examples: failed AC PRIMARY PUMP, takeoff/landing configuration, low fuel mode). Fuel is scavenged from the left and right wing feed tanks and dumped into their DC AUX PUMP collector boxes. The action of the ejectors keeps the collector boxes full, which maintains the DC AUX PUMPs primed until the fuel is consumed from the wing feed tanks.

The DC AUX PUMP collector boxes are an open box sealed at the bottom. They incorporate a flapper check valve to ensure DC AUX PUMP gravity feed in the event a wing tank scavenge ejector fails. The wing tank water drains are located in the DC AUX PUMP collector boxes.

The existing vent system scavenge ejector outlet is redirected on to the wing tank scavenge ejector. The DC AUX PUMP is inoperative during most of a typical flight. The stirring action of the vent system scavenge ejector discharge prevents ice and wax formations at the wing tank scavenge ejector to ensure proper operation if needed later in the flight.

Center Tank Scavenge System

The center tank scavenge ejectors receive motive flow from the AC PRIMARY BOOST PUMPS. The ejector outlet is fed back through the wing/center rib 47.6 into the wing. The center tank transfer line goes through the wing/center rib 47.6 into the wing.

Once the center tank transfer pumps run out of fuel, the center tank scavenge ejectors take over and scavenge the remaining fuel from the tank. Even when the center tank is empty, the ejectors continue to operate. This keeps unusable fuel quantity low in the center tank due to fuel migration.

A check valve is installed in the motive flow line to the center tank scavenge ejector to prevent air from an empty center tank from entering the feed line via the center tank scavenge ejector inlet during suction feed mode.

A check valve is installed at the inlet of the center tank scavenge ejector to prevent spillage of the motive fuel flow back into the center tank when the transfer pump is in operation, or when the center tank is empty.

Unusable Fuel Data

Fuel remaining in the aircraft after fuel scavenge system operations:

• Wing tanks 3.3 gallons each
• Center tank 3.4 gallons
• Aft tank 0.2 gallons
• Unusable fuel 67.5 lb without aft tank 68.85 lb including aft tank

The fuel quantity system is calibrated for either configuration. When an operator reaches that aircraft´s unusable fuel level, fuel quantity indicated in the cockpit is zero.

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Component Location Index
IDENT	DESCRIPTION	LOCATION	IPC REF
-	CENTER TANK EJECTOR PUMPS	ZONE(S) 160	28-27-01 [ GX ] [ GXRS ] [ G5000 ]
-	FEED TANK EJECTOR PUMPS	ZONE(S) 520/620	28-27-05 [ GX ] [ GXRS ] [ G5000 ]
-	CENTER TRANSFER/SCAVENGE CHECK-VALVES	ZONE(S) 160	28-27-09 [ GX ] [ GXRS ] [ G5000 ]
-	CENTER MOTIVE FLOW CHECK-VALVES	ZONE(S) 160	28-27-13 [ GX ] [ GXRS ] [ G5000 ]
-	CENTER TRANSFER PUMP CHECK-VALVES	ZONE(S) 160	28-27-17 [ GX ] [ GXRS ] [ G5000 ]

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