The injector(A) of the Common Rail System is electronically controlled. It has been designed to allow multiple injection with short intervals, to be fully electronically controlled, and to release a small amount of heat. The nozzle of injector opens when the solenoid valve is triggered and permits the flow of fuel. They inject the fuel directly into the engine’s combustion chamber. The fuel is stored in the Rail ready for injection and the injected fuel quantity is defined by the injector opening time and the rail pressure. The excess fuel, which was needed for opening the nozzle of injector, flows back to the tank through a collector line. The return fuel from the pressure-control valve and from the low-pressure stage is also led into this collector line together with the fuel used to lubricate the high-pressure pump.