A by-pass and pressure regulator valve exhibiting: an inlet mouth and an outlet mouth set in reciprocal communication by a main conduit; a by-pass mouth. The by-pass and pressure regulator valve comprises: an obturator, mobile between at least a closed position, in which it interrupts fluid communication between the main conduit and the by-pass mouth, and at least an open position, in which the fluid communication is not interrupted; operating pressure control means, predisposed to move the obturator from the closed position; means for determining a flow pressure loss in fluids crossing the main conduit, arranged along the main conduit in order to separate a first tract upstream of the main conduit from a second tract downstream thereof; obturator command means governed by a fluid pressure difference between the first tract and the second tract of the main conduit, distinct from the operating pressure control means but operatively connected to the obturator.