... years1,vacuum tube length:47/1500mm,58/1800.2,vacuum tubes:15pcs,18pcs,20pcs,24pcs,30pcs3,Outer tank material:202stainless steel ... principle:1,The high quality vacuum tubes ansorb the solar ultraviolet ray;then heat the cold water in the vacuum tube2,The hot ... valve,the tap water flow in the tank ,if the water is full,it will close the valve automatically solar collector tube for solar water heater