An arrangement comprising a pocket space between drying cylinders in a paper or board machine and means for sealing the pocket space, which arrangement comprises the following arranged to define said pocket space - a first and a second drying cylinder (2, 3), - a travelling wire for supporting a paper or board web to be dried, - a wire turning element between the first and the second cylinder (2, 3) in the travelling direction of the wire, the wire being arranged to be supported by the first and the second cylinder (2, 3) and the wire turning element and to be movable in relation to the cylinders and the wire turning element in the travelling direction of the wire, - a first runnability component fitted in the space between the first and second drying cylinders (2,3) for stabilizing the run of the web, which runnability component is elongated in the cross direction of the paper or board machine and which comprises at least - a first sealing surface (19, 22), which is a Coanda surface curved in the travelling direction of the wire, and which is elongated in the cross direction, and which first sealing surface (19, 22) is arranged, at a first sealing point, to a sealing distance A from the wire in a normal running situation, the sealing distance A being chosen between 5-15 mm, - a first blow nozzle provided with a nozzle slot having a nozzle size B chosen between 0.5-3.5 mm and elongated in the cross direction, arranged to blow air towards the first sealing point at a first blow point, and which nozzle slot is arranged to blow air along the first sealing surface (19, 22), wherein the nozzle size B is the size of the nozzle slot in a perpendicular direction in respect of the cross direction, which defines the thickness of the air layer to be blown as seen perpendicularly away from the sealing surface (19, 22), characterized in that - the sealing surface (19, 22) is fastened to the runnability component by a hinge such that the sealing surface can be turned to a desired safety distance from the wire, when needed, - the distance between the first blow point and the first sealing point as measured along the first sealing surface is 2-5 times the sealing distance A. - a first and a second drying cylinder (2, 3), - a travelling wire for supporting a paper or board web to be dried, - a wire turning element between the first and the second cylinder (2, 3) in the travelling direction of the wire, the wire being arranged to be supported by the first and the second cylinder (2, 3) and the wire turning element and to be movable in relation to the cylinders and the wire turning element in the travelling direction of the wire, - a first runnability component fitted in the space between the first and second drying cylinders (2,3) for stabilizing the run of the web, which runnability component is elongated in the cross direction of the paper or board machine and which comprises at least - a first sealing surface (19, 22), which is a Coanda surface curved in the travelling direction of the wire, and which is elongated in the cross direction, and which first sealing surface (19, 22) is arranged, at a first sealing point, to a sealing distance A from the wire in a normal running situation, the sealing distance A being chosen between 5-15 mm, - a first blow nozzle provided with a nozzle slot having a nozzle size B chosen between 0.5-3.5 mm and elongated in the cross direction, arranged to blow air towards the first sealing point at a first blow point, and which nozzle slot is arranged to blow air along the first sealing surface (19, 22), wherein the nozzle size B is the size of the nozzle slot in a perpendicular direction in respect of the cross direction, which defines the thickness of the air layer to be blown as seen perpendicularly away from the sealing surface (19, 22), characterized in that - the sealing surface (19, 22) is fastened to the runnability component by a hinge such that the sealing surface can be turned to a desired safety distance from the wire, when needed, - the distance between the first blow point and the first sealing point as measured along the first sealing surface is 2-5 times the sealing distance A.