The invention relates to a fuel injector unit (20) comprising: a first fuel feeding section (410) comprising at least one first fuel injection valve (442), wherein the first fuel injection valve (442) is provided with a first fuel gallery (444) and a first control section (480) arranged opposite ends of the first fuel injection valve (442); and second fuel feeding section (610) comprising a second fuel injection valve (642) for controlling injection of second fuel to the engine (100), wherein the second fuel injection valve (642) is connected to a second fuel inlet (14) in the fuel injector unit (20). A sealing fluid chamber (448) is arranged between the first control section (480) and the first fuel gallery (444) of the first fuel injection valve (442), and the sealing fluid chamber (448) is arranged in flow communication with the second fuel feeding section (610) such that the second fuel is arranged to act as sealing fluid. The invention relates also to a fuel feeding arrangement (10) and to an internal combustion piston engine (100).