... -axial structure high borosilicate 3.3 glass vacuum tube with tube wall thickness of 1.6mm.Inner ... /1800.2,vacuum tubes:15pcs,18pcs,20pcs,24pcs,30pcs3,Outer tank material:202stainless steel with 0.31mm4, ... has 15years long life span ,and the vacuum tubes can work individually,so if the only ... many residentbuildings.Working principle:1,The high quality vacuum tubes ansorb the solar ultraviolet ray;then ...