The use of float valves in hydroponics nutrient reservoirs ensures a constant level of nutrient can be maintained, and the hydroponic system is less likely to run dry.
A float valve is usually installed into the main nutrient reservoir, and connected to a 'header' tank with backup nutrient (or just plain water). As the main nutrient reservoir level drops, fresh supplies are feed (usually by gravity) into the main reservoir.
The float valves below can even be connected to mains water.
