An expansion tank has a chamber in which air is locked inside a bladder or diaphragm. It screws into standard 1/2-inch or 3/4-inch threaded plumbing fittings. When pipes are filled with heat transfer fluid (water and glycol), and the operating pressure of the system is set, the fluid will occupy a given volume based on the temperature. As the fluid is heated by the sun, it expands. The expansion tank allows the fluid to safely expand by compressing the air in the chamber. The size of the expansion tank needed depends on the total volume of fluid, which is determined by the number and size of collectors, and the length and diameter of the pipes in the solar loop.

The small control meter is installed inside the house and by using a small sensor, which is located inside the tank, the user can know how much hot water is available and what the water temperature is for use in the tank. The user can also control whether the water will be heated by the electrical heating element, enabling him to control his usage of electricity.

Main functions:
1.Display clock and week
2.Display temperature
3.Temperature difference circulation pumps provide three working scopes for choose
4.Three periods timing heating
5.Heat collector frost protection
6.Memory function
7.Water tank temperature setting
8.Display the system pressure