System for operating a fluid actuator

System comprising:

• an actuator that is provided with a piston movably mounted to be moved linearly by thrust of a fluid within two chambers separated by the piston,
• a needle shutter connected to the piston for regulating an 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 with a path for bringing pressurized fluid from a reservoir to the chambers 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, connected to the supply circuit and configured so that in resting condition it leaves open a fluid drainage path that connects the chambers and the reservoir to allow a flow of fluid between the chambers 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 and the solenoid valve comprises two excitation positions:
• a position wherein it allows fluid communication between the chambers 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 and the reservoir.