Abstract: A pneumatically driven device which in the exemplary form of the invention is an air tool driven by pistons. In the exemplary form there are two pistons having racks which drive the reciprocatable shoe through pinion gears. One piston drives in each direction. Each piston at the end opposite the driven end has an annular groove in it with a sealing ring with ports for communicating air to the area behind the ring for pushing it out against the inside surface of the cylinder. During a piston stroke at this end of the piston air is compressed to provide a cushioning and braking effect which improves the overall operation, and avoids excessive wear.