Abstract: A motor is provided of the piston or diaphragm type in which vacuum is constantly applied to one side of a piston or the like and air under pressure is constantly applied to the opposite side to drive the piston through a stroke. The vacuum and pressurized air may be obtained from sources outside the motor. A valve mechanism driven by the motor reverses the application of vacuum and air pressure when the piston reaches each end of its stroke so that power is continuously applied to both sides of the piston during both forward and reverse movement thereof. Different pistons are arranged out of phase with one another to provide a smooth flow of mechanical power. In one version, the motor drives an air pump having a vacuum inlet and an air pressure outlet, and by connecting such inlet and outlet to the valve mechanism, the motor will drive a load as well as itself. In another version, the motor has an internal combustion apparatus incorporated therewith.