of fig1 and therefore only those components which are different have been illustrated in fig2 the fig1 throttle 59 for the control circuit of pump 11 is replaced with a specially configurated throttle unit 70 in which a constant cross section throttle 71 and an adjustable cross section 72 are connected in parallel to make this possible the conduit 51 has branches 73 74 which are re united behind the throttle unit 70 the cross sections of the throttles 71 72 are so chosen that the flow cross section of the constant throttle 71 is smaller than the maximum flow cross section of the adjustable throttle 72 this modification of fig2 permits a more precise coordination of the adjustments of pump 11 relative to the output characteristics of the combustion engine which is being employed to power the drive the embodiment of fig3 is also identical to that of fig1 except for the fact that the throttles 55 and 59 in conduit 51 have been replaced with two throttles 80 81 which are both adjustable moreover the throttles 80 and 81 are coupled with one another so that adjustment of one of them i e of its flow cross section results in concomitant adjustment of the other throttle depending upon the pressure curve desired for the pump 11 the throttles 80 and 81 may be so coupled with one another that the flow cross section of throttle 81 is.