A fuel injector unit for assembly to a cylinder head of an internal combustion piston engine and for injecting first and second fuel to the internal combustion piston engine, the fuel injector unit comprising: - A first fuel feeding section comprising at least one first fuel injection valve for controlling injection of first fuel to the engine when assembled to the engine, wherein the first fuel injection valve is provided with a first fuel gallery and a first control section arranged opposite end of the first fuel injection valve, the first control section being provided with a control chamber, wherein a control piston is arranged, controlling opening and closing of a control needle in the first fuel feeding section, and the first control section is a hydraulic control section, and wherein the first fuel gallery is connected to a first fuel inlet in the fuel injector unit and wherein the first fuel gallery is provided with injection orifice or orifices opened in response to a position of the first fuel injection valve, and wherein the first fuel feeding section is further provided with a main flow fuse valve arranged between the first fuel inlet in the injector unit and the first fuel injection valve, - A second fuel feeding section comprising a second fuel injection valve for controlling injection of second fuel to the engine when assembled to the engine, wherein the second fuel injection valve is connected to a second fuel inlet in the fuel injector unit, and the second fuel feeding section comprises a second fuel injection valve, a second fuel gallery and a second control section wherein position of the second injection valve is effected by a pressure of the second fuel in the second control section, and that the second fuel feeding section is provided with a flow fuse valve arranged between the second fuel inlet and the second fuel injection valve. - and a sealing fluid chamber arranged between the first control section and the first fuel gallery of the first fuel injection valve, wherein - the sealing fluid chamber is arranged in flow communication with the flow fuse valve of the second fuel feeding section such that the second fuel is arranged to act as sealing fluid minimizing the first fuel to flow from the first fuel gallery to the first control section and - the flow fuse valve of the second fuel feeding section is arranged to open and close flow communication from the second fuel inlet to the sealing fluid chamber of the first fuel feeding section, and - the sealing fluid chamber is provided with a discharge conduit for allowing a discharge of the second fuel therefrom to a common discharge with the first fuel feeding section. - A first fuel feeding section comprising at least one first fuel injection valve for controlling injection of first fuel to the engine when assembled to the engine, wherein the first fuel injection valve is provided with a first fuel gallery and a first control section arranged opposite end of the first fuel injection valve, the first control section being provided with a control chamber, wherein a control piston is arranged, controlling opening and closing of a control needle in the first fuel feeding section, and the first control section is a hydraulic control section, and wherein the first fuel gallery is connected to a first fuel inlet in the fuel injector unit and wherein the first fuel gallery is provided with injection orifice or orifices opened in response to a position of the first fuel injection valve, and wherein the first fuel feeding section is further provided with a main flow fuse valve arranged between the first fuel inlet in the injector unit and the first fuel injection valve, - A second fuel feeding section comprising a second fuel injection valve for controlling injection of second fuel to the engine when assembled to the engine, wherein the second fuel injection valve is connected to a second fuel inlet in the fuel injector unit, and the second fuel feeding section comprises a second fuel injection valve, a second fuel gallery and a second control section wherein position of the second injection valve is effected by a pressure of the second fuel in the second control section, and that the second fuel feeding section is provided with a flow fuse valve arranged between the second fuel inlet and the second fuel injection valve. - and a sealing fluid chamber arranged between the first control section and the first fuel gallery of the first fuel injection valve, wherein - the sealing fluid chamber is arranged in flow communication with the flow fuse valve of the second fuel feeding section such that the second fuel is arranged to act as sealing fluid minimizing the first fuel to flow from the first fuel gallery to the first control section and - the flow fuse valve of the second fuel feeding section is arranged to open and close flow communication from the second fuel inlet to the sealing fluid chamber of the first fuel feeding section, and - the sealing fluid chamber is provided with a discharge conduit for allowing a discharge of the second fuel therefrom to a common discharge with the first fuel feeding section.