The actuator comprises a cylinder and a rod. The cylinder comprises an inner cylindrical tube and an outer cylindrical tube which extend coaxially to each other along a longitudinal axis (z). The inner cylindrical tube accommodates a plunger which is rigidly connected to the rod and separates an inner volume of the inner cylindrical tube into a compression chamber and an extension chamber, wherein at least the compression chamber contains oil. The inner cylindrical tube and the outer cylindrical tube enclose with each other a reservoir chamber which is permanently in fluid communication with the extension chamber via at least one first passage provided in the inner cylindrical tube and contains a pressurized gas in a first portion thereof and oil in a remaining portion thereof. The cylinder further comprises an intermediate cylindrical tube which extends along the longitudinal axis (z) between the inner cylindrical tube and the outer cylindrical tube and encloses, along with the inner cylindrical tube, an intermediate chamber permanently in fluid communication with the compression chamber via at least one second passage provided in the inner cylindrical tube. The actuator further comprises a check valve associated to the inner cylindrical tube to allow the oil to flow in the direction from the reservoir chamber to the compression chamber only, and an electrically-operated flow control valve which is associated to the intermediate cylindrical tube for controlling the flow of the oil between the intermediate chamber and the reservoir chamber. The flow control valve is movable between a first operating position, in which it allows the oil to flow between the intermediate chamber and the reservoir chamber, and a second operating position, in which it prevents the oil from flowing between the intermediate chamber and the reservoir chamber.