... , the circulation system will start work. It will transmit the solar energy from solar collector to the tank.solar water heater features ... pure red copper TU1+water,transfer power>=150W,Working pressure,4Mpa,welding pressure 4MpaDust Ring GasketSilicon Rubber Vacuum Tubetri-element tube, ... Structure,Gradual change SS-AL-Nx/Cu selective absorption coating,Vacuum Degree,P<=5*10-4,Service Life,10 years ...