... principle:This system uses the thermo siphon principle. Solar vacuum tube is plugged into the bottom of water tank. This water ... tubes with outer diameter of 47mm, 58mm and 70mm, and tube length ranges are available at 1200mm, 1500mm, 1600mm, 1800mm, 1900mm ... both at home and abroad, including the US, Germany, Poland, India, Pakistan, Singapore, Vietnam, Korea, Turkey, Syria, the Middle East, Europe ...