Float Switch- How They Work

Float Switch

A switch that controls the level of any liquid (e.g., water or oil, etc.) in a tank in a fully automated manner, is called a float switch. A float switch is used to automatically check the level of water, oil, liquid type chemical, or any other similar liquid in a tank, to measure the level of liquid, and to keep the level of liquid within the pre-set limits (so that the liquid level neither exceed nor decrease from this pre-determined level). The float switch is mostly used for water tanks in homes. In figure 4.13, a water pump motor has been illustrated along with a float switch. The function of a float switch installed within a water tank is to automatically turn ON the water pump if the water level decreases beyond a certain level and turn OFF the water pump automatically after it’s filling up to a certain limit, so that in the presence of electricity, water pump does not get empty, therefore this type of switch is normally known as an ON / OFF switch. 

Figure – Schematic diagram for pump motor control with float switch

Float Switch

A float switch consists of a mechanically ON/OFF switch mechanism. This switch mechanism turns ON or OFF through a float operating rod (i.e., a rod which turns the switch mechanism ON or OFF through up or down movement of a float type ball as a result of a decrease or an increase in the tank’s water level). In other words, this switch mechanism works through an up or down movement of a float or ball on the water surface as a result of a change (i.e., increase or decrease) in the water level of a liquid in the tank. 

Suppose that a float switch has been used to control the level of water in a tank, whereas a motor pump has been used to fill the water tank with water. In such a situation, a float switch is fitted or left in the water tank through an operating rod in such a way, that float may move up or down easily due to a change in the water level, as has been illustrated in the figure. After this, connections of a motor pump and switch mechanism are set. When the level of water existing in a water tank falls below a preset level, the float drifting on the water surface also moves down with a decrease in the water level. As the float moves down, the operating rod also shifts downwards, whereas contrarily, the smaller end of the operating rod connected through quadrant adjustment, which turns the switch mechanism ON/OFF, moves upward. Remember that difference existing between a high-water level and low water level is adjusted through quadrant adjustment, according to which the ON, and OFF contacts of the switch mechanism operate. As soon as float drops down from the preset limit, the other smaller end of the operating rod turns ON the switch mechanism. As soon as the switch mechanism turns ON, the motor pump receives supply and starts operating. As a result of the operation of the motor pump, the water tank starts filling up. As the water level rises, the float also moves up and the smaller end of the operating rod existing on the switch mechanism moves down. When the tank fills up to the desired level, the switch mechanism (i.e., mechanical switch) turns OFF as a result of reaching up the water surface. As such, the supply to the motor pump stops and the motor pump turns OFF (i.e., water stops pouring into the water tank). This process continues automatically until supply fails. As such, water always exists in the water tank and it does not get empty. 

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Engr Fahad

My name is Shahzada Fahad and I am an Electrical Engineer. I have been doing Job in UAE as a site engineer in an Electrical Construction Company. Currently, I am running my own YouTube channel "Electronic Clinic", and managing this Website. My Hobbies are * Watching Movies * Music * Martial Arts * Photography * Travelling * Make Sketches and so on...

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