The invention relates to a valve device comprising a valve body defining a fluid flow duct having a throttle element disposed therein and turned about its axis by actuator means via a drive shaft, the throttle element having an internal cavity defined by a circular wall that is open in its bottom portion. The circular wall also presents, over a portion of its periphery, an opening of varying shape so as to define a fluid flow passage in the duct that is variable between a fully-open position in which the opening co-operates in full with the duct, and a fully-closed position in which said circular wall closes the duct. The device further includes an annular sealing gasket disposed in the flow duct, said gasket being in contact with the wall of the internal cavity in the throttle element. The internal cavity of the throttle element is spherical in shape so that in the fully-closed position of the valve, the entire circumferential of the sealing gasket is in contact with the wall of the internal cavity of the throttle element.