an improved bypass valve , suitable for the connection of terminal units in which a heat exchange occurs between the environment to be conditioned and a thermal - carrier fluid , in particular a liquid , with the lines of delivery or supply and return of the fluid , with these units typically defined by heat exchangers , fan coil units , batteries for air handling units of the ahu type in the field of hvac , including an h - shaped valve - body with two opposed and parallel tubular elements defining a delivery duct and a return duct joined one to the other and communicating via a transverse element defining a bypass duct , the valve - body integrating , in a monobloc structure , an on - off delivery valve , an on - off return valve and an on - off bypass valve , the latter provided with a linear shutter to enable / disable the circulation of a thermal - carrier fluid through the bypass duct .