... keymark 2.Anti-freezen & pressurized 3.10 years warranty Vacuum tube solar collecotr a. Module design, arbitrary combination, harmonize ... as the medium and the controller hasthe anti-freezing functiond. Multifunction: bathing, washing, domestic heating etc.e. Work at ... Working pressure,4Mpa,welding pressure 4MpaDust Ring GasketSilicon Rubber Vacuum Tubetri-element tube,High boron and silicon content 3 ...