Abstract: Valve for regulating and measuring the flowrate of a fluid through a header (1) and a bypass duct (2,2b) inside the said header, comprising means (10,10a) for shutting off the aperture (2b) of the bypass duct (2), which are movable axially upon operation of associated actuating means (30), means (44) for detecting the pressure exerted by the fluid flow, an instrument (43,43a) for measuring the flowrate of the fluid, the scale (43a) of which is provided on the external surface of said actuating means (30), said means (10,10a) for shutting off the aperture (2b) of the bypass duct (2) being joined to said actuating means (30) so that rotation of the latter results in only the axial movement of the former and the shut-off means (10,10a) are independent of the measuring instrument (43,43a) during their movement in the axial direction.