for eventual discharge of hydraulic fluid in correspondence with the connector 32 the base 12b has a cylindrical seat 36 in which a piston 38 is slidable axially by means of a rod 40 operated by the lever 12a the piston 38 has transverse holes 42 for putting the connector 30 into communication with the connector 32 in the non neutral or control configuration of the servocontrol 12 in the neutral configuration of the servocontrol 12 there is no communication between the two connectors that is between the lines t and d the difference between the servocontrols 12 of the invention and the servocontrols normally used relates to a hole 44 present in the crown of the piston 38 which in the non neutral configuration of the servocontrol 12 puts the connector 30 into communication with the discharge connector 34 in normal servocontrols the connector 34 is used to discharge only the small quantity of hydraulic fluid of the order to a few cm 3 per minute which leaks between the piston 38 and its seat 36 according to the invention however in the non neutral position of the servocontrol 12 a predetermined flow of hydraulic fluid considerably greater than that resulting from the leakage passes through the holes 42 and the hole 44 the sensor 18 which is of the electro hydraulic type comprises a hollow body 46 having respective connectors 48 and 50 for connecting it to the pump 14 and the.