The system includes an actuation device having a d.c. electric motor (10, 20) and a high-ratio gearbox (11). The output of the gearbox connects with the spool (13) ofthe valve through a segmented rack and pitman pin or a rack and pinion arrangement (12). A control circuit for the electric motor includes position feed-back (17) to permit accurate positioning of the spool. Further, spring means are included to bias the spool to its neutral position in the absence of a control signal or on occurrence of a fail condition. A suitable control device for the control system is also disclosed, the device having a command leve with a pair of catering springs. Detent means for the lever is also shown.