How Mechanical and Electric Fuel Pumps Work

The fuel pump is one of the essential parts of a vehicle’s fuel delivery system. Its main purpose is to draw fuel from the fuel tank and supply it to the engine. There are two types of fuel pumps – mechanical and electric.

Mechanical fuel pumps were widely used in older model vehicles while electric ones are common in all modern vehicles. Let’s see how they differ in the way they work.

Mechanical fuel pump

They are used in vehicles with carburetors. They draw fuel from the fuel tank and transfer it to the carburetor. Since there was not much pressure involved in supplying fuel in the carburetor, a diaphragm that could expand and produce vacuum was the central component in the pump.

How it works

• It, typically, has three components – camshaft, lever arm and diaphragm

• When the camshaft rotates, the eccentric lobe on the camshaft pushes the lever arm upwards

• This pulls the other end of the lever arm and the diaphragm attached to it moves down, expanding the space in the pump

• When the space expands, vacuum is created inside the pump and fuel is sucked up into the inlet line from the tank, while the outlet is still closed

• The expanded diaphragm is then pushed back to its normal position by a spring attached to it. This closes the inlet valve and opens up the outlet valve. Thus, the fuel is pushed towards the carburetor

• The carburetor, further, blends the fuel with air and transfers it to the engine

Electric fuel pump

They are used in cars with electronic fuel injection system. Most modern vehicles contain an electric fuel pumps. They operate more efficiently and deliver higher pressure (40-60psi). The pump is located inside the tank. This helps in maintaining appropriate temperature of the pump.

How it works

• Its working is very similar to that of a mechanical

• Like the mechanical fuel pump, the electric ones also has the check valve and diaphragm pull system, but the pull on the diaphragm is provided by an electric switch also called the ‘solenoid’

• The diaphragm is not directly connected to the solenoid, but only to an iron rod. The solenoid attracts this iron rod using electromotive force pulling the diaphragm down, drawing fuel into the chamber

• When this happens, the solenoid pulls apart the contacts through which electricity passes. This cancels off the power supply and the spring pulls the diaphragm back to its normal position pumping the fuel into the outlet valve

• The outlet valve opens enabling this outflow

• When this happens, the electrical connectivity is restored and the solenoid starts pulling the iron rod again

Despite the widespread use of electric fuel pumps, some users still prefer mechanical ones due to their ease of installation, reliability and the chance to prevent the risk of electrical issues. However, electric ones are far superior to their mechanical counterparts as they are safer, more convenient, durable, and resistant to contamination and provide optimal fuel efficiency.

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