Another type of air drive used in tools such as road breakers, riveting hammers and stapling machines is the reciprocating piston. This consists of a piston that is driven up and down inside the working cylinder by expansion of the compressed air. A system of valves or ports is used to direct the compressed air to each end of the piston in turn, giving a rapid oscillating motion. In most designs the piston movement is transmitted by allowing the piston to strike against the working head, which then transmits the blows to the workpiece.
For many applications the pneumatic motor or reciprocating piston is incorporated in a hand tool for direct use by an operator. When such tools are used for assembly-line work they are often mounted overhead on counterbalanced suspension systems that allow them to be pulled down for use and released to return to the storage position until required again. Another common use of air motors on assembly and machining lines is in hoist systems where the fine control that can be achieved is of particular value in positioning parts.