A reciprocating drive mechanism having a housing with upper and lower internal chambers with a spool slidably positioned inside the upper internal chamber. There is at least one fluid inlet and fluid exhaust communicating with the upper internal chamber and at least one slide valve positioned within the upper internal chamber and traveling with the spool. A piston positioned in the lower internal chamber divides the lower internal chamber into an upper and lower cylinder space. A valve stem is connected to the piston and includes a bore communicating with the upper internal chamber and an exhaust passage is positioned between the upper and lower internal chambers.