A Pump Up Float Switch, also known as 'Normally Closed', opens the circuit on the rise and is typically used to turn the pump off when the float is in the up position. So, a pump could be set to turn off when the water level in the storage tank reaches a predetermined high level. Therefore, a pump up float switch is often used to fill a water tank. 

A Pump Down Float Switch, also known as 'Normally Open', closes the circuit on the rise and is typically used to turn the pump off when the float is in the down position. So, a pump could be set to turn off when the water level in the storage tank reaches a predetermined low level. Therefore, a pump down float switch is often used to empty a water tank. 

The terms ‘Normally Open’ and ‘Normally Closed’ are often used to describe float switches.

• Normally Open = Pump Down
• Normally Closed = Pump Up