Media support

1. A media support system, comprising:

a continuous loop belt having an inner perimeter, an outer perimeter, and multiple holes each extending through the belt from the inner perimeter to the outer perimeter;

a drive mechanism to circulate the belt in a first direction along an upper run to support a media sheet and in a second direction opposite the first direction along a lower run;

multiple suction cups arranged along the outer perimeter of the belt so that multiple suction cups are exposed simultaneously along a length of the upper run of the belt to hold down media sheets supported on the upper run of the belt, each suction cup having a port aligned with one of the holes through which air may be evacuated from the suction cup; and

a vacuum control system to connect each suction cup port along the upper run of the belt to a vacuum source, the vacuum control system comprising:

multiple rows of multiple enclosures, each enclosure defining a vacuum chamber to underlay the upper run of the belt;

a linear slot along a top of each enclosure to align with holes in the belt;

a tubular duct;

circumferential slots in the duct arranged to include at least one group of multiple slots and at least one single slot; and

multiple conduits each extending between the duct and one of the enclosures; and where the duct is:

translatable to align some or all of the conduits to a circumferential slot according to the translational position of the duct; and

rotatable to connect some or all of the aligned conduits to a circumferential slot according to the rotational position of the duct.

2. The system of claim 1 , comprising the vacuum source connected to the duct.

3. The system of claim 1 , comprising a sleeve around the duct to cover the circumferential slots when not aligned with a conduit.