Instead, a metal ball rolls back and forth inside of the float. When the ball rolls to one side, the contacts within the float switch will close. When the ball rolls to the other side, the contacts will open.
When this float switch is hanging from where it is tethered, the switch will be in the open position. Therefore, it is called a normally open float switch. When water level risers, the float switch will start to float upward, and the switch will close.
This type of float switch is often used when a tank needs to be emptied periodically. When the tank is empty, the float will be open, and power would not be sent to a pump within the tank. When the water level rises, the float switch will close and send power to the pump. Then the pump will remove water from the tank and lower the water level. Once the water level drops low enough, the switch will open and deactivate the pump. At this point the cycle will start over.