There are two types of 12v fuel transfer pump: mechanical and electrical. The majority of modern cars are equipped with electric fuel pump systems due to their many advantages over mechanical pumps.
The transition from carburetors to fuel injections has mainly contributed to the decline of mechanical pumps and the rise of their electrical counterparts since fuel injection systems work best at fuel pressures that are much higher than what mechanical pumps can generate. An electric pump is usually located inside the fuel tank so that the fuel in the tank can be used to cool the pump, thus ensuring a steady and ample supply of fuel.
These pumps run whenever they are turned on, making them prone to cause fire when there are fuel leaks due to accidents or malfunctions. This is also one reason fuel pumps are installed inside the tank since liquid fuel does not explode.
Another safety feature installed with an electric pump is the ECU or electric control unit, which can be programmed to conditionally shut the pump off even while the engine is running.
Also, some cars are equipped with an inertia switch, which is a roll-over valve that automatically shuts off the fuel pump in the event that the car rolls over. These safety features effectively negate the electric pump's potential for danger, making it not only efficient, but also virtually hazard-free.
Electric fuel pumps are normally replaced every 70,000 to 100,000 miles, depending on the condition of the car. It is recommended to replace these pumps at the first signs of failure to ensure safety for the passengers and optimum performance for the vehicle.