the control line 66 decreases below the opening pressure of the control orifice 50 of the pressure balance the biasing valve 60 39 may be designed in the manner of a spring loaded slide it would furthermore be conceivable to provide an actuation magnet instead of the pressure precontrol via the control line which is de energized upon the decrease of the pressure if the hydraulic motor 2 is moved against the load pressure fluid is conveyed into the working pressure line 11 by the hydraulic pump 4 the 2 3 way valve 57 in the control line 56 is in its locking position the control orifice 50 is relieved at the opening side and operates as a directional seat valve being in the locking position the pressure built up in the working pressure line 11 is available at the pressure balance 50 the hydraulic motor 2 is moved at the selected speed as a function of the selected position of the measuring orifice 7 excessive pressure fluid is discharged to the tank 5 by the control orifice 52 of the pressure balance 54 via the bypass line 51 thanks to the influence of the control presures in the control lines 62 and 61 and of the spring 63 the control orifice 52 ensures the keeping constant.