Control valve for controlling a gas through-flow, comprising an elongate housing , which delimits a flow channel and is divided into an inflow portion , a drive portion , and an outflow portion , which are arranged adjacent to one another along a longitudinal axis (L), wherein the gas flows through the flow channel from the inflow portion via the drive portion to the outflow portion when the control valve is used as intended, a gearing mechanism , which is provided within the drive portion and has an externally drivable output shaft parallel to the longitudinal axis and a rotary slide element , which is arranged displaceably along the longitudinal axis via the output shaft and has an outer valve seat surface , which closes an annular gap, defined between itself and an inner surface of the outflow portion , by a longitudinal displacement in the flow direction, and a flow element , which is provided on the gearing mechanism at its end facing the inflow portion and has a dome-shaped outer surface, which directs the gas coming from the inflow portion into an annular gap between the gearing mechanism and the inner surface of the drive portion; characterized in that the inflow portion has a cylindrical flow channel , which has a constant diameter (D1) substantially over the entire longitudinal extent and widens conically at the transition to the drive portion, and in that at least one opening for inserting at least one measuring element , preferably a flow measuring element, is provided in the inflow portion; and the rotary slide element is conical with a circular base surface and a lateral surface , which is provided between the valve seat surface and the tip of the rotary slide element, wherein a blind hole parallel to the longitudinal axis is provided at the tip of the rotary slide element. an elongate housing , which delimits a flow channel and is divided into an inflow portion , a drive portion , and an outflow portion , which are arranged adjacent to one another along a longitudinal axis (L), wherein the gas flows through the flow channel from the inflow portion via the drive portion to the outflow portion when the control valve is used as intended, a gearing mechanism , which is provided within the drive portion and has an externally drivable output shaft parallel to the longitudinal axis and a rotary slide element , which is arranged displaceably along the longitudinal axis via the output shaft and has an outer valve seat surface , which closes an annular gap, defined between itself and an inner surface of the outflow portion , by a longitudinal displacement in the flow direction, and a flow element , which is provided on the gearing mechanism at its end facing the inflow portion and has a dome-shaped outer surface, which directs the gas coming from the inflow portion into an annular gap between the gearing mechanism and the inner surface of the drive portion; characterized in that the inflow portion has a cylindrical flow channel , which has a constant diameter (D1) substantially over the entire longitudinal extent and widens conically at the transition to the drive portion, and in that at least one opening for inserting at least one measuring element , preferably a flow measuring element, is provided in the inflow portion; and the rotary slide element is conical with a circular base surface and a lateral surface , which is provided between the valve seat surface and the tip of the rotary slide element, wherein a blind hole parallel to the longitudinal axis is provided at the tip of the rotary slide element. <EOS>