... keymark 2.Anti-freezen & pressurized 3.10 years warranty Vacuum tube solar collecotr a. Module design, arbitrary combination, harmonize ... glass 3.37) Solar working station8) With heat pipe: anti-freezing > -35 degrees centigrade9) Water capacity: 150L, 200L, 250L, ... ,Working pressure,4Mpa,welding pressure 4MpaDust Ring GasketSilicon Rubber Vacuum Tubetri-element tube,High boron and silicon content 3 ...