A pneumatic tool, such as a nailer, includes a housing, a cylinder disposed within the housing, and a piston slidably movable within the cylinder. The piston has a driver for driving fasteners, such as nails. An upper piston chamber and a lower piston chamber are defined within the cylinder on an upper...http://www.google.ca/patents/US6145727?utm_source=gb-gplus-sharePatent US6145727 - Pneumatic tool
