A control valve (10) for a fluid circulation circuit comprises a valve body (12) having a bottom wall into which an axial orifice emerges and a side wall (16) into which side orifices (20, 22, 24) emerge, the valve body delimiting a housing of revolution for a regulating member (26) capable of rotating about a rotation axis XX and of taking various angular positions to control the distribution of the fluid through the orifices. The regulating member (26) is surrounded by a sealing segment (42) in the shape of an open ring and elastic means are provided to separate two ends (44, 46) of the sealing segment in order to deform it radially outward and thus ensure that the sealing segment is pressed against the valve body housing. Application particularly to the fluid circuit of motor vehicles.