an apparatus for closing a slider - operated zipper on a moving filled package , comprising means for performing the following steps : conveying a package forward in a straight line ; guiding a slider on a zippered portion of the package through a channel as the package moves forward ; blocking forward movement of the slider at a predetermined position inside the channel as the package continues to move forward ; and releasing the slider when the force being exerted by the slider in the forward direction reaches a level substantially equal to a predetermined threshold . this apparatus can be employed in association with a continuous band sealing apparatus . the means for blocking forward movement of the slider at a predetermined position inside the channel are a pair of spring - loaded plungers , e . g ., ball plungers . if the slider end stop is weak , the slider will be pulled off the advancing package and will fall onto an ejection ramp .