A fuel injector, a fuel injector assembly and an associated method

A fuel injector 1 comprising a valve member 11, in a valve bore 23 and a spring chamber 40. The spring chamber contains a biasing member 50, for example a spring, which biases the valve member into contact with a valve seat 20. A fuel supply passage 80 is connected to an outlet chamber 22 of the fuel injector and a secondary cleaning fluid supply passage 90 is connected to a second end 25 of the bore for providing fluid to clean the injector. The cleaning fluid prevents leakage of the fuel from the outlet chamber towards the second end of the bore along a clearance 29 between the valve member and the bore. An annular drainage channel 26 may remove any leaked fuel along with the cleaning fluid. A drainage port (27, figure 3) may drain the annular channel through a drainage passage (28, figure 11).