Fuel injection system for a combustion engine

The device has a control piston (50) acting on an injection valve element (28) with a surface area subject to the pressure in a control pressure chamber (22) determined so that with a second control valve (70) closed, if the control pressure chamber is separated from a discharge chamber (24) the force on the control piston is adequate to close the fuel injection valve when the valve is only partly open but not if it is fully open.