A printing system includes a driving belt configured to drive media through the printing system relative to one or more print heads and a vacuum conveyor system. The vacuum conveyor system includes a vacuum chamber cover having a first surface and a second surface opposite the first surface, as well as a plurality of openings through the cover from the first surface to the second surface. A number of seals are disposed to match the location of openings. Each seal extends along the length of the vacuum chamber cover and is drivable to open or close a region with openings. A vacuum chamber below the second surface of the vacuum chamber cover is configured to apply a vacuum to the media through one or more of the openings that are open. The applied vacuum constrains the media on the driving belt by flattening it against the driving belt.