“Part Fill” Valve? Yes, Part Fill valves are widely used in Rainwater tanks. The valve will open once the water level in the tank has fallen to a low position, this allows the town mains water to enter the tank and, when the water level reaches the minimum level, the valve closes. This arrangement is used to maintain a minimum volume of town mains water in the tank for use with the pump, while leaving most of the tank empty waiting for rain to fill it to the top.
Wanna learn more about the Arduino platform? If you have an irresistible temptation to do some experiments using Arduino microcontroller, just try this simple “electronic” version of a “part fill” valve, wired using an Arduino, a standard hobby servo, and a home-made water sensor. When the Arduino notices the water level inside the rainwater tank is very low , it commands the servo to let the water flow from an alternate source!
Arduino Wiring Diagram
Download/copy the simple sketch (Arduino program) included here, verify and upload it to the Arduino board with the help of the Arduino IDE. Here two pieces of stiff wire is used to sense the conductivity in the gap between the water sensor points. When there is more water, there is a higher conductivity. Arduino reads this conductivity, and at the level set by the sketch, turns the servo to release or constrict the flow of water. Needless to say, you should make your own water sensor pad using short-length of closely spaced wires, needles or solder pads. Besides, little skill and patience required to hook up the servo horn with the existing/new valve. The servo horn should crook the town mains water inlet valve open/close to control the flow of water. Zip ties can be used to secure the mechanical connection. Once in situ, try to hot glue the servo.
For more detail: Arduino Based Part Fill Automatic Valve