SCHLAGWERK

An impact mechanism operated with gaseous fluid under pressure fed from a source of fluid having a casing with an inner cylindrical space. A piston is accommodated for reciprocation within the cylindrical space of the casing to divide the space into a work stroke chamber and an idle stroke chamber. The chambers are in communication with the source of gaseous fluid through a distribution means for reciprocation of the piston under the action of fluid. A valve is provided over the inlet port of at least one chamber to admit gaseous fluid under pressure thereto. The valve comprises biasing means in the form of a helical compression spring mounted coaxially with the inlet port of the chamber. One end of the spring is tightly sealed and the other end is fixed over the inlet port of the casing. Gaseous fluids under pressure is admitted to the chamber through gaps between the turns of the spring when the spring is expanded, and the admission is interrupted when the spring is compressed. There is also provided a working implement received in the casing and operated by the piston.