... keymark 2.Anti-freezen & pressurized 3.10 years warranty Vacuum tube solar collecotr a. Module design, arbitrary combination, harmonize with ... pressure,4Mpa,welding pressure 4MpaDust Ring GasketSilicon Rubber Vacuum Tubetri-element tube,High boron and silicon content 3.3, ... Quantity(set)20102787763574022116916613613040HQ278213209172171Price(USD) Heat pipe solar thermal vacuum tube solar collector