the casing 19 as the sideplate is displaced in operation when the driving cylinder 8 starts functioning the controlling sideplates 3 4 move in the axial direction relative to the impeller this can be seen from the pump embodiment shown in fig1 this movement of the sideplates relative to the impeller allows the outlet width b 2 of the impeller to change the capacity q of the centrifugal pump is proportional to the size b 2 of the impeller width therefore the replacement of the sideplates leads to the corresponding change of the pump discharge i e its capacity when the controlling sideplate moves the pilot shaft 7 connected with it moves as well one pilot shaft is inserted into an induction coil 9 used as a detector the pilot shaft which is made from a conducting material causes a signal to appear at a microprocessor 10 of the control system during its motion in the embodiments of the hydrodriving mechanism shown in fig4 6 when the valve 16 is open the fluid pressure is supplied to the annular cylinder chamber 12 resulting in the moving of the sideplate relative to the impeller this movement decreases the outlet width b 2.