certain pressure difference between the control line 9 and the second pressure chamber 15 is reached this function can be achieved for instance by providing that the pressure stage component 33 covers part of the end face of the step up piston 17 protruding into the first pressure chamber 13 once the step up piston 17 is in its outset position the remaining area of the step up piston 17 being larger than the end face of the step up piston 17 that protrudes into the second pressure chamber 15 by the choice of the proportions of these areas and the prestressing of the restoring spring 27 the pressure difference up to which the high pressure side of the step up piston 17 acted upon by the pressure of the feed line 21 and the restoring spring 27 keep the step up piston 17 in its outset position counter to the pressure of the control line 9 is defined also shown in fig4 are a third and a fourth check valve 35 and 37 the third check valve 35 is disposed in the feed line 21 between the first check valve 23 and the injection pump 3 and it has the same blocking direction as the first check valve 23 the fourth check valve 37 is disposed in a connecting line 39 between.