Device and method for controlling axial forces acting upon a moving web comprises first, second and third rotatable rollers. The third roller is between the first and second rollers and is movable in a circular path in the vertical plane between lower and upper positions in response to axial forces acting at any moment upon the web. To enable a simple manual installation of the web, the upper position of the third roller is at a sufficient vertical distance above the first and second rollers to form an open horizontal passage through which the web can pass freely between the first and second rollers and the above-situated third roller. Axial forces are controlled by biasing the third roller with a force which counters the motion of the third roller in the direction of the upper working position and which is less than the ultimate tensile strength of the web.