Abstract: The present invention relates to a solar water heating system operating in a closed circuit and making use of a change of phase in a working fluid as a heat transfer medium, comprising: at least one collector to be exposed to sunlight for transmitting radiant solar energy to a working fluid and thus converting the fluid into a liquid-vapor mixture; a hot water storage reservoir connected to a heat exchanger; a pump for returning the working fluid to the collector; and a pipe means connecting all of the above mentioned components.

Abstract: A vapor pressure pump for delivering a liquid into a system operating at a higher pressure or located at a higher level by action of a vapor pressure produced from a portion of the liquid to be delivered. The pump comprises a closed reservoir for liquid, which includes an unidirectional liquid inlet, an unidirectional liquid outlet, a vapor exhaust valve adapted to balance the pressure between the unidirectional liquid inlet and the reservoir during its filling. The pump also comprises a vapor generator for producing vapor inside the reservoir at a pressure sufficient to force out the liquid contained therein through the liquid outlet, and a control device for operating the vapor generator only when the liquid fed by the liquid inlet has reached a predetermined level in the reservoir.