A zipper slider is made to open and close the teeth of the zipper. Be sure that the zipper is completely unzipped before opening the case to prevent damage to the teeth. The slider is designed to slide back and forth along the zipper. Therefore, you should not pull upward on the slider because it will loosen its jaws and eventually make the slider too loose to close the zipper properly. This is usually the first sign of a worn zipper and you should adjust it as soon as possible to avoid further problems.
To stop this problem, you can tighten the back of the slider with a set of pliers. Open the zipper all the way before starting so the slider is touching the material of the cover.
Lightly clamp the pliers along the side of the slider and press down. Make sure to apply the most pressure to the back of the slider. Be careful not to apply too much pressure at first. Use light pressure a few times until the slider is tight enough to slide along the zipper and properly close the teeth.
From www.bamcases.com
