turn actuated by servo means 9 the servo means 9 can suitably be a direct acting pneumatic cylinder or an electric motor that via a worm gear actuates the regulating rod via a rack integrated with the regulating rod the regulating rod is suspended in such a manner at two bearing points 15 16 arranged in the walls of the air port that the regulating rod runs essentially parallel to the upper wall 22 of the air port by means of this suspended mounting the a servo means 9 can actuate the regulating device 10 so that the regulating device moves in a direction at 45 u00b0 in relation to the horizontal plane and inclined upwardly and outwardly from the interior of the recovery boiler fig2 shows the arrangement seen in the same view as in fig1 the regulating device 10 is shown here in two alternative positions position ps in which the air opening 30 is closed and position po in which the regulating devices 10 u2032 has been drawn back to its maximum extent in position po the airflow out to the air port opening is completely unrestricted from the air shaft 20 via the air port 21 which air port has essentially at least the same flow cross.