lie at right angles or vertically to the control edge 4 as shown in broken lines in this figure by this arrangement the same throttle cross section is formed in each case when the control piston 1 is turned and the control edge 4 taken past the four openings 10 when the internal combustion engine 39 s fuel injection plant is not operating the control edge of the control piston 1 takes up the position along the dot and dash line 4a whereas at full load the control edge runs roughly along the line 4b in the position shown the control edge 4 and the openings 10 form a throttle cross section which corresponds to a position in the lower load range and is shown hatched for greater clarity it will be seen that a quadratic ratio exists between the movement of the control piston 1 as it turns and the consequent change in throttle cross section at the control edge 4 and the openings 10 this follows from the fact that a doubling of the displacement of the control piston involves a four fold enlargement or reduction of the throttle cross section this enables a very accurate dosage corresponding to the fuel requirement at any particular time to be achieved from the lowest up to the middle load range in the constructional form shown in fig3 the same reference symbols have been used as in fig1 but with an added index essentially this constructional form differs from the construction form in fig1 only in that the spiral groove 5 39 has a square thread with a number of pitches corresponding to the number of openings 10 39 so to control.