Nema Pressure Tank

When you open a spigot in your home, you expect water to flow at a certain speed. Water pressure in the line causes that water to flow. If your home is on city utilities, water pressure is controlled (for the most part) by the city. If your home is on a well, you need something to build that pressure and this is the purpose of the pressure tank.
In a nutshell: The pressure tank in a water well system creates water pressure by using compressed air to bear down on the water. Because of this pressure, when a valve is opened water is pushed out of the tank through the pipes in your home. When the water in the pressures tank drops below the required amount, a pressure switch is activated turning on the pump. The pump then refills the pressure tank. The combination of the pressure tank, pressure switch and the pump is what allows water to flow through your home.