Fuel pump
A low-pressure fuel supply used by a carbureted engine can be achieved through a gravity feed system, i.e. by simply mounting the tank higher than the carburetor.Pumps for modern direct-injection engines operate at a much higher pressure, up to 30,000 psi (2,100 bar)[2] and have configurations such as common rail radial piston, common rail two piston radial, inline, port and helix, and metering unit.When the plunger is at top dead center, the injection to the cylinder is finished and it is returned on its downward stroke by a compression spring.[4] Due to the fixed height of a cam lobe, the amount of fuel being pumped to the injector is controlled by a rack and pinion device that rotates the plunger, thus allowing variable amounts of fuel to the area above the plunger.These pumps contain a chamber whose volume is increased and/or decreased by a moving plunger, along with check valves at the inlet and discharge ports.