... system and 15 years for vacuum tube. As one of the biggest exporters of solar water heaters,Xingshen Solar Water ... : MG rod, electrical heating, assistant tankLogo: OEM, co lour printing /stickerWorking PrincipleSolar vacuum tube was evacuated into the tank ... tube and become hot, because of different density between cold and hot water, there will be a natural circulation in the tube, and hot water ...