The photo below shows a web from a double doffer card on the front apron of a crosslapper. This is the apron that takes the web from the card conveyors into the crosslapper. The arrows point to vacuums on each edge of the web. The purpose of these vacuums is threefold. 1. The vacuums catch extraneous clumps of fiber at the edge of the web. 2. The vacuums keep the width of the web constant as it enters the crosslapper. It is important to keep the width of the web constant going into the crosslapper. You may think the width of the web coming out of the card is constant but it is not; especially if the card and crosslapper have automatic profiling capabilities. 3. They create a feathered edge that blends better and reduces the appearance of a crosslapper mark in the finished product. These vacuums work best on fibers of short staple length. If the fibers are too long, the vacuum will try to rip off too much of the web. The fiber sucked off is recycled and recarded.