Fuel injection device for internal combustion engines

In connection with a fuel injection device for internal combustion engines, a valve unit is proposed which is located in the transition between pump working chamber, high-pressure accumulator and low-pressure source and which comprises a check piston and a return piston which, with their mutually facing end faces during the compression stroke, form a sealing boundary that encloses the connection between pump working chamber and high-pressure accumulator and seals off against the low-pressure source.