The final cylinder in an offset printing press, which is responsible for transferring the printed sheet to the delivery pile. A delivery cylinder is a type of transfer cylinder, others of which may exist in the press between printing units. The delivery cylinder is charged with the responsibility of carrying the printed sheet from the final impression cylinder to the grippers attached to the delivery chains. A delivery cylinder, in most configurations, is covered with skeleton wheels, a set of disks (which can frequently be adjusted to ensure that they only support the sheet in non-image areas) that hold the sheet as it travels to the delivery chains. (Such a delivery cylinder is also known as a skeleton cylinder.) In other configurations, the delivery cylinder—like a typical transfer cylinder—is coated with a near-frictionless substance, then covered with a near-frictionless cloth which is allowed to slide freely over the surface of the cylinder, further ensuring that the wet ink won't be smudged or marked. A marked alternative to the traditional delivery cylinder is known as a BacVac, a system devised by Printing Research, Inc., in which the unprinted side of the sheet is pulled away from the skeleton wheels by a vacuum and rollers, preventing contact between the wheels and the wet ink. This system, however, cannot be used on presses which print both sides of a sheet simultaneously. (See Offset Lithography: Printing Unit.)
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