A self-compensating piezoelectric actuator for a control valve

An actuator device for a control valve is described and comprises a piezoelectric actuating member (12) for bringing about the movement of a closure member (30) of the valve between an open position and a closure position; the member (12) has a reference portion (20) for connection to a fixed portion (26) of the device and a free portion (24) for connection to the closure member (30), the free portion (24) being movable relative to the reference portion (20) as a result of mechanical deformations produced in the actuating member (12) by the piezoelectric effect. The reference portion (20) of the actuating member (12) is controllable selectively between a free condition in which it is movable relative to the fixed portion (26), and a condition in which it is locked in a reference position and is fixed firmly to the fixed portion (26) of the device by magnetic attraction.