Proportional valve with shape memory alloy actuator

A proportional valve for controlling the outlet pressure of a fluid flowing therethrough, which comprises a valve body having an inlet port and an outlet port for the fluid and an inner chamber, the chamber including a valve seat that is opened and closed variably by a shutter movable axially towards and away from the valve seat, shutter movement being controlled by a shape memory alloy actuating member operating antagonistically to an elastic member, the temperature of the fluid being lower than the transition temperature of the shape memory alloy, the actuating member and the elastic member being connected to the body valve at opposing sides relative to the valve seat, and a power control circuit circulating an electric current through the actuating member so as to heat the same by Joule effect from a temperature generally lower than the transition temperature, wherein the elastic member on the shutter prevails, to a temperature that is generally greater than the transition temperature, wherein the actuating member on the shutter prevails, at least one vent hole is formed in the valve body for putting a portion of the chamber upstream of the valve seat into fluid communication with the outside or a fluid collection network, the actuating member being housed in that portion of chamber corresponding to the inlet port of the fluid, whereby a continuous flow of fluid around the actuating member is ensured for accelerating the cooling process, a closed-loop control power circuit being provided for controlling the circulating current as a function of pressure signal generated by a fluid pressure sensor and in such a way as to offset the retarding effect produced by the fluid during heating of the actuating member.