... 3)Sample offer 4)OEM service Working Principle Of Solar Tube Water:Tri-target solar vacuum tube, connecting with water tank or manifold, when it ... cold water, cold water again flows into solar vacuum tube for another heating process. 1, Vacuum tube is consists of two layer of glass tubes2 ... loss.5, The air is evacuated from the space between the two glass tubes to form a vacuum, so it eliminates heat ...