System comprising: - an actuator that is provided with a piston movably mounted to be moved linearly by the thrust of a fluid within two chambers (20, 24) separated by the piston, - a needle shutter connected to the piston for regulating the injection flow of molten material from a nozzle into a mold, so that the shutter can move from a closing position, wherein there is no passage of molten material through the nozzle, to an opening position, wherein there is passage of molten material through the nozzle, and vice versa; - a supply circuit (30, 32) for bringing pressurized fluid from a reservoir to the chambers (20, 24) with a flow direction and an opposite flow direction, the two fluid flow directions corresponding to a forward and a backward movement of the piston, respectively; and - a solenoid valve (60; 70), connected to the supply circuit (30, 32) and configured so that in resting condition it leaves open a fluid drainage path that connects the chambers (20, 24) and the reservoir to allow a flow of fluid between the chambers (20, 24) and the reservoir determining a movement of the piston that brings the shutter to a closing position, wherein the solenoid valve • is inserted directly into the path of the supply circuit (30, 32), and characterised in that the solenoid valve • comprises two excitation positions: - a position wherein it allows fluid communication between the chambers (20, 24) and the reservoir by imposing in the supply circuit a fluid flow direction opposite to that obtainable in the rest position, and - a position wherein it inhibits fluid communication between the chambers (20, 24) and the reservoir. - an actuator that is provided with a piston movably mounted to be moved linearly by the thrust of a fluid within two chambers (20, 24) separated by the piston, - a needle shutter connected to the piston for regulating the injection flow of molten material from a nozzle into a mold, so that the shutter can move from a closing position, wherein there is no passage of molten material through the nozzle, to an opening position, wherein there is passage of molten material through the nozzle, and vice versa; - a supply circuit (30, 32) for bringing pressurized fluid from a reservoir to the chambers (20, 24) with a flow direction and an opposite flow direction, the two fluid flow directions corresponding to a forward and a backward movement of the piston, respectively; and - a solenoid valve (60; 70), connected to the supply circuit (30, 32) and configured so that in resting condition it leaves open a fluid drainage path that connects the chambers (20, 24) and the reservoir to allow a flow of fluid between the chambers (20, 24) and the reservoir determining a movement of the piston that brings the shutter to a closing position, wherein the solenoid valve • is inserted directly into the path of the supply circuit (30, 32), and characterised in that the solenoid valve • comprises two excitation positions: - a position wherein it allows fluid communication between the chambers (20, 24) and the reservoir by imposing in the supply circuit a fluid flow direction opposite to that obtainable in the rest position, and - a position wherein it inhibits fluid communication between the chambers (20, 24) and the reservoir. • is inserted directly into the path of the supply circuit (30, 32), and characterised in that the solenoid valve characterised in that the solenoid valve • comprises two excitation positions: - a position wherein it allows fluid communication between the chambers (20, 24) and the reservoir by imposing in the supply circuit a fluid flow direction opposite to that obtainable in the rest position, and - a position wherein it inhibits fluid communication between the chambers (20, 24) and the reservoir. - a position wherein it allows fluid communication between the chambers (20, 24) and the reservoir by imposing in the supply circuit a fluid flow direction opposite to that obtainable in the rest position, and - a position wherein it inhibits fluid communication between the chambers (20, 24) and the reservoir.