The invention consists of a differential temperature engine in which the return stroke is achieved independently of the contraction of the vapor which induced the initial movement of the moving member. The engine consists of a relatively cold and a relatively warm chamber which are sealed from the outside environment, and contain a low boiling point fluid. One end of a cylinder communicates with the vapors in the relatively warm chamber while the opposing end of the cylinder communicates with the vapors in the relatively cold chamber. When there is no communication between the cold and warm chambers a vapor pressure differential upon the opposing ends of a piston within the cylinder causes the piston to move towards the cold chamber. The return stroke of the piston is induced by equalization of the pressures upon the two opposing ends of the piston. This is obtained either by the establishment of a communication between the cold and the warm chamber, or by establishment of a communication of the two opposite ends of the cylinder with the warm chamber.
A solar powered engine 10, e.g. for pumping water, comprises a solar collector 116 in which a low boiling point liquid is vaporized, an engine comprising a piston 84 reciprocably movable in a chamber 82 where the resulting vaporized liquid does work, a condenser 126 where the vaporized liquid is condensed back into a liquid, means for returning the condensed liquid to the solar collector 116 and a transmission 88 which connects the piston 84 to a load. When the vaporized liquid is being introduced below the piston 84 to move the piston 84 to perform useful work, the condenser 126 is at the same pressure as a reservoir 142 so that condensed liquid may flow from the condenser 126 to the reservoir 142, and when the vaporized liquid is exhausting from below the piston 84 to permit the piston 84 to descend again, the reservoir 142 is at the same pressure as the solar collector 116 so that the condensed liquid may flow from the reservoir 142 to the solar collector 116 to complete the cycle.
A relatively hot and a relatively cold chamber are air evacuated and contain a low boiling point liquid. The temperature differential between the chambers results in a vapor pressure differential between the chambers. The vapor pressures inside the chambers transmit a vector force to a movable wall of each of the chambers. The vapor pressures in the chambers are equalized intermittently by an intermittent communication between the chambers. The chambers are positioned relative to each other so that the movable wall of one chamber transmits an opposing vector force to the movable wall of the other chamber. This brings the walls to a position which is determined by the the resultant of the opposing vector forces upon the walls. When the resultant of the vector forces changes during the intermittent communication between the chambers the movable walls change their position. The movements of the walls between different positions perform useful work through standard mechanical links to a force receiving means.
