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How Fuel Pump Works
How It Works: Submerged Fuel Pumps
You can lead an electronic fuel-injection (EFI) system to gasoline, but you can't make it drink. In fact, EFI systems won't work at all unless they're force-fed a constant supply of fuel under fairly high pressure.
In the early days of EFI, electric pumps could be found outside the gas tank. But they faded from view because in-tank pumps held many advantages. In-tank pumps are quieter and tucked away from engine heat and weather-related corrosion. Perhaps most important, they pressurize the fuel along the entire length of the system. Because higher pressure raises the fuel's boiling point, vapor-lock is virtually nonexistent in vehicles with an in-tank pump. It's also easier for a pump to push a liquid through a line than to pull it, so in-tank pumps are smaller and lighter. Most in-tank pumps are mounted in a hanger that fits into a hole on top of the gas tank. The hanger also holds the gas gauge sending unit, the fuel pickup and a pickup screen called a fuel sock. The whole assembly sits in a cup-shaped fuel reservoir that's usually fastened to the bottom of the tank. Unused fuel spills from the return line into the cup whenever the pump is running. The filled cup assures that sufficient fuel surrounds the pump pickup during braking, cornering and acceleration, even when the tank is near empty.
Electrical power for the pump usually comes from a pump relay. Turn the key on in a car with an in-tank pump, and the relay switches the pump on for a couple of seconds, filling the cup reservoir and pressurizing the system. After it travels up the pickup tube, it enters the inlet side of the pump, where it rushes directly through the pump motor to cool and lubricate it. From there, the fuel goes into a geroter (sliding vane) or roller vane pump assembly, where it's pressurized. Yes, that's right, the fuel runs directly through the motor, where electricity sparks across the motor's brushes. If you think back to your high-school chemistry class, you'll recall that combustion (or, in this case, an explosion) requires three things: fuel, ignition and oxygen. Fortunately, oxygen is not present in the fuel pump, so there's no ka-boom. Before the fuel exits the pump into the fuel line, it passes through a one-way check valve. The valve keeps fuel from draining out of the line and back into the tank when the pump is off.
Once the fuel has left the pump, it travels through the fuel line to the pressure regulator mounted on the engine on many vehicles. On others it travels first through a pulse damper that's mounted directly above the pump.
You can lead an electronic fuel-injection (EFI) system to gasoline, but you can't make it drink. In fact, EFI systems won't work at all unless they're force-fed a constant supply of fuel under fairly high pressure.
In the early days of EFI, electric pumps could be found outside the gas tank. But they faded from view because in-tank pumps held many advantages. In-tank pumps are quieter and tucked away from engine heat and weather-related corrosion. Perhaps most important, they pressurize the fuel along the entire length of the system. Because higher pressure raises the fuel's boiling point, vapor-lock is virtually nonexistent in vehicles with an in-tank pump. It's also easier for a pump to push a liquid through a line than to pull it, so in-tank pumps are smaller and lighter. Most in-tank pumps are mounted in a hanger that fits into a hole on top of the gas tank. The hanger also holds the gas gauge sending unit, the fuel pickup and a pickup screen called a fuel sock. The whole assembly sits in a cup-shaped fuel reservoir that's usually fastened to the bottom of the tank. Unused fuel spills from the return line into the cup whenever the pump is running. The filled cup assures that sufficient fuel surrounds the pump pickup during braking, cornering and acceleration, even when the tank is near empty.
Electrical power for the pump usually comes from a pump relay. Turn the key on in a car with an in-tank pump, and the relay switches the pump on for a couple of seconds, filling the cup reservoir and pressurizing the system. After it travels up the pickup tube, it enters the inlet side of the pump, where it rushes directly through the pump motor to cool and lubricate it. From there, the fuel goes into a geroter (sliding vane) or roller vane pump assembly, where it's pressurized. Yes, that's right, the fuel runs directly through the motor, where electricity sparks across the motor's brushes. If you think back to your high-school chemistry class, you'll recall that combustion (or, in this case, an explosion) requires three things: fuel, ignition and oxygen. Fortunately, oxygen is not present in the fuel pump, so there's no ka-boom. Before the fuel exits the pump into the fuel line, it passes through a one-way check valve. The valve keeps fuel from draining out of the line and back into the tank when the pump is off.
Once the fuel has left the pump, it travels through the fuel line to the pressure regulator mounted on the engine on many vehicles. On others it travels first through a pulse damper that's mounted directly above the pump.