Pressurized solar water heater 150L Solar keymark, CE, ISO Red copper heat pipe, transfer heat quick 58-1800mm tube 1. Working principle: The pressurized water tank has ... no water in the vacuum tube, so it can be working even have an tube broken. 2) The red copper in the inner tube, the ... heat transfer more quickly. 3) It is a closed loop, so the heat can be preserved for a ...