What is Float Switch : Working & Its Applications

Float switches are used in various industrial processes for point-level detection which means these switches give an indication that a liquid level is normally open or normally closed at a specific level. These switches work for detecting foaming, dielectric, conductivity, pressure, temperature, vacuum, vapours, condensation, boiling effects, vibrations, and bubble formation. So these switches are appropriate for almost all types of liquids. This switching operation is contact-free and doesn’t need a voltage supply. So due to the simple functional principle of this switch, it can be used in a wide range of applications ranging from general industrial applications to process plants & shipbuilding industry. This article discusses an overview of a float switch – working with applications.

What is Float Switch?

A float switch definition is: It is a type of contact liquid level sensor which uses a float to operate a switch within a tank. This switch is also known as a level sensor. These switches play a key role in controlling other devices like pumps & alarms when a level of liquid increases or drops to a particular point. The float switch symbol is shown below. These switches range from small sizes to large sizes. Float switches come in two different styles: magnetic(Electromagnetic) and Mechanical float type.

Switch Symbols
Switch Symbols

Construction of Float Switch

The construction of this electromagnetic switch can be done with a stem, reed switch, and permanent magnet.

Construction of Float Switch


The stem of the switch is a plastic part that connects the switch to the keycap directly. The stem can be plastic or metal depending on the requirement.

Reed Switch


The reed switch is hermetically sealed within a stem of the float switch. These are most frequently designed with stainless steel or plastic. The water float covers a sealed magnet to move up & down the stem length when a level of fluid increases and decreases.

Permanent Magnet

A permanent magnet in a switch moves consistently with the level of fluid on a guide tube. A reed contact is connected in the guide tube which is energized throughout the non-magnetic walls of the float by the float magnet approach.

Float Switch Working Principle

The working of a float switch is based on the principle of buoyancy i.e., when there is no liquid in contact with the float, it floats on top of the liquid surface and triggers an alarm signal, when there is a sufficient amount of liquid in contact with float, it submerges itself into liquid and stops alarming. The principle of operation is the same for both the style of float switches but works depending on their construction of it. Let’s see how both work.

Electromagnet switch Working:

As we have already discussed its design the construction section. Let’s get into the working of it. The magnet which is mounted on the stem moves up and down as liquid levels rise and fall. The reed switch attaches to the side of the tank or container holding the liquid being monitored by the float switch. When the magnet comes into contact with the reed switch, it completes the electrical circuit between these two devices — triggering an alarm or controlling some other device that monitors the false switch (like turning off the power).

Mechanical Float Switch Working:

The mechanical float switch is the most common type of water level switch and is used to detect the presence of water in a tank or vessel. The device consists of a float that rises and falls with the liquid level. This type of Float switch consists of an arm or lever which moves up and down with the level of the liquid in which it is installed. A rod goes through the center of this arm and has one end fixed on top while another end is attached to a lever which will work as an actuator. When there is more liquid present in the container, then more weight is added on top and this causes movement of the lever which turns on the power supply to the appliance connected with it.

When there is less liquid present in the tank or pool, less weight is added on top and therefore arm does not move downwards according to gravitational force but remains static at its position because of an equal amount of weight from both sides.


The specifications of the float switch include the following.

  • Rated voltage ranges from 220-240V.
  • The maximum current is 10 Amps.
  • The protection grade is IP-68.
  • It is ideal for level control within overhead or underground water tanks.
  • It can automatically start or stop the pump.
  • It doesn’t require a sensor.
  • Its operation is completely mechanical.
  • It can be used through an alarm to inform about flooding within the basement.

Types of Float Switch

These switches are available in two types horizontal and vertical.

Horizontal Float Switch

These switches are arranged at the sidewalls of the water tank and this switch is used where the top & bottom of the liquid tanks are not accessible. The movement of float in the tank will cause the reed switch to operate at a certain level because of the changing liquid level. By using this switch, the float can be connected to a hinge. Once the float approaches the reed switch, then it shifts a magnet near the switch to open or close the circuit.

Horizontal Float Switch
Horizontal Float Switch

Vertical Float Switch

The vertical arrangement of two floats like a stem & a magnetic is known as a vertical float switch. In two floats, one float is stable & connected to the top of the fluid tank whereas another float is not fixed with respect to the level of liquid.

Vertical Float Switch
Vertical Float Switch

The float fits in the region of the stem & it increases and decreases through the liquid level. The stem includes one or above-sealed reed switches. Once the water float approaches one of the reed switches, then magnetic force will cause the switch to open otherwise close. So because of the change in liquid level, the movement of liquid float will cause the switch to function at a certain level.

Float Switch Arduino

The interfacing of an Arduino with the float switch is shown below. The switch in this project is used to detect the water level and depth in the tank. Here float switch is an electromagnetic switch that operates as a closed switch because it comes into contact once the water applies the power on it.

Interfacing an Arduino with the Float Switch
Interfacing an Arduino with the Float Switch
  • This switch is made up of plastic material.
  • The power rating of this switch is about 10W.
  • The temperature rating of this switch is about 10 to 85o C.
  • The float’s maximum switch current is about0.5A.
  • The voltage of this switch is 100V DC.

The connection of this switch with an Arduino can be made like the following. Generally, this switch includes two terminals like VCC and GND. The GROUND terminal of the switch is connected to the Arduino Board’s GND pin whereas the remaining pin of the switch is connected to the Arduino Board’s Input pin. The operation of this switch can be understood very easily by connecting an LED to the Arduino. Here LED  glow on when float switch goes on upon detecting the water level high.

The program for Interfacing the float switch with an Arduino is shown below.

int FloatSensor=2;
int led=3;
int buttonState = 1; //reads pushbutton status
void setup()
pinMode(FloatSensor, INPUT_PULLUP); //Arduino Internal Resistor 10K
pinMode (led, OUTPUT);
void loop()
buttonState = digitalRead(FloatSensor);
if (buttonState == HIGH)
digitalWrite(led, HIGH);
Serial.println( “WATER LEVEL – HIGH”);
digitalWrite(led, LOW);
Serial.println( “WATER LEVEL – LOW” );

Once the program is executed successfully then dump the above code into the Arduino board by choosing the port from Arduino IDE. After the code dumping is successfully done into the Arduino, this switch working can be understood.

The below steps will explain the complete program.

  • At first, variables float sensor, LED, and button state is initialized to default values.
  • Then, the serial communication is initialized to the display device.
  • The float switch state is read through an input pin and then stored within the variable “button state”.
  • Once the “button state” of the variable becomes HIGH, then it means the switch has detected the high level of water & it is displayed on the serial monitor & the LED will glow simultaneously.
  • In the same way, the opposite case can be achieved once the level of water is LOW.
  • Like this, the above program can be executed constantly with a 1-second delay.

Once the program is uploaded successfully, we can observe that when the level of water in the tank goes up, the LED which is connected will be turned ON & once the water level goes down, then the LED will turn off.

Advantages and Disadvantages

The advantages of float switch include the following.

  • Simple & low-cost mounting.
  • Doesn’t require an auxiliary power supply.
  • It can be used for any kind of liquids like Acids, Chemicals, etc.
  • Potential-free and switching voltage up to 230V.
  • Surface disturbances like bubbling, foaming, and ripples will not affect its performance.
  • It can be used with a temperature sensor or temperature switch.
  • The fluid conductivity & Dielectric constant will not affect operation.

The disadvantages of float switch include the following.

  • Moving parts exposed to corrosion, clogging, and damage.
  • Fouling can cause unreliable movement or seizure of float actuation.
  • Float actuation mainly depends on fluid contact.
  • Turbulence within the liquid may cause the float to move.
  • Sticky or thick fluids may stop the float from moving.
  • Regular maintenance is required to check nothing is controlling the movement of the float.


The applications of float switch include the following.

  • This switch is used to turn ON and OFF a pump or open or close an electronic valve.
  • This switch activates tank level alarms to protect & inform of a possible hazardous spill.
  • This switch is used to protect heaters and also other equipment from severe injuries and dangerous situations.
  • This switch is very helpful in monitoring the level of liquid within different industrial & residential applications and is normally connected to a valve or pump or an alarm to inform a user.
  • Industrial washers use these switches for monitoring the washer water level.
  • Air conditioning & refrigerant use these switches for controlling the water levels.
  • These switches are used in the beverage industry for filling or emptying the beverage tanks.
  • Water tank float switches can help in water level control for potable water, rainwater, wastewater, and sewage application. This pump switches on/off with the rise/fall of the float switch in the water.
  • These are used in sump pumps & sewage pits can sense and activate a pump to avoid increasing water levels.

Thus, this is all about an overview of a float switch and its working with applications. The main function of this switch is to detect the water level within the tank or any container.  Here is a question for you; Float switch is also called?