FLOAT SWITCH FOR WATER TANK
“Float switch ; As name suggests, is a type of switch that floats into the water. Float switch is used to control a pump or a valve depending upon the requirement.”
The float switch consists of hollow plastic chamber in which a limit switch is attached with mechanical lever. A cable is connected to the limit switch, most probably 3 core cable if limit switch is a ‘changeover switch’. A heavy weight is tied on the cable, In some float switches weight is not required.
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WORKING OF FLOAT SWITCH
‘Changeover relay’ & ‘mechanical lever’ arrangement are the key components in float switch. Entire working depend upon that two things.
That’s why it is very much important to understand the changeover relay & mechanical lever first.
CHANGEOVER RELAY
Changeover relay is a type of switch which controls the circuit through another circuit, Indirectly. It consists of three contacts ‘Common‘, ‘NC(Normally closed) ‘& ‘NO(normally open)‘.
A Schematic diagram of electromagnetic relay is shown below. In that arrangement, It is seen that an electromagnetic coil is place behind the changeover relay. Contact’s jumper is connected with a spring Which pulls the common contact towards the NC contact.
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At initial normal state, common contact is connected with NC contact while at forced state; common contact gets connected to the NO contact. The forced state of relay can be achieve by physical force like in roller-lever limit switch or through electrical signal as in Electromagnetic relay.
When external force on relay get removed then due to the mechanical spring, Common contact get pulled back towards the NC contact.
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MECHANICAL LEVER :
A mechanical lever is rigid solid element which moves on a single point. Mechanical lever normally contains two ends. Force produced on one end produces the parallel movement on another end. A bit movement on one side produces an larger movement on another side.
A GIF of mechanical lever shown below :
Now back to the topic !
In metallic ball based float switch; A heavy metallic ball is placed along with a lever & a changeover relay.
A cable is connected to the changeover relay & brought out of the plastic chamber. The whole float chamber is IP68 ingress protected. Inner view of float switch is shown below:
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- Free Fall state :
When water is empty & float switch is hanging freely. The metallic ball pushes the lever downward; In turn; lever’s another side presses the push button of changeover relay. Relay get shifted to forced state from normal state. COMMON contact get connected to NO contact.
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2. Uplift state :
When water is full. The float switch pushed upward. Which results metallic ball get shifted to opposite of lever & due to removed force, relay get back to its normal state. Where ‘COMMON‘ contact get connected back with ‘NC ‘ contact.
Positioning of weight on float switch’s Cable
The weight which is placed on the cable of float switch; play a very important role.
When float switch is hanging freely into an empty tank, Connected weight don’t do anything. But it works When float switch is immersed into the water. Let understand this !
- Let suppose, Weight is taken off from the float switch. float switch is immersed into the water without weight.
The float switch don’t lift up completely instead it starts floating on the surface of water Which results metal ball don’t able to shift its position. - On the other hand, Connected weight on the cable makes float switch to lift up completely which forces metal ball to shift its position.
The length between connected weight & float switch is also important to consider which determines at what water level; float switch lifts up.
APPLICATIONS OF FLOAT SWITCH
Float switch has only a changeover relay through which we can implement multiple circuits for multiple applications. Next, we will discuss some of the applications & their circuits one by one.
Circuit to fill the tank For Single phase pump
Neutral is directly connected to the pump & Phase is passes through the 2way selector switch & ‘NO ‘ contact of the changeover relay.
At these connections, When selector switch in closed position(acting like on/off) & float switch fall freely into the empty tank making the ‘NO ‘ contact closed. Pump gets power supply & starts pumping the water into the tank until the float switch get lifted up OR selector switch shifted to open position. This circuit helps to prevent overflow condition.
Float switch rating should be consider according to pump’s rating. Otherwise, changeover relay can get damaged.
CIRCUIT :
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Circuit to fill the tank For Three phase pump running on DOL Starter
In single phase circuit, Pump is directly controlled through changeover relay but In 3 phase motor, Motor should be controlled through a Contactor.
Motor terminals & 3phase supply is connected across the contactor. To implement tank filling circuit on 3phase pump running on DOL Starter; We just need to replace single phase Motor with a 3 pole contactor with coil voltage 230VAC,50Hz. As shown in an image below
CIRCUIT:
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Circuit to empty the tank for Single phase pump
Again neutral is directly connected to pump. Phase is passes through the selector switch & ‘NC ‘ contact of the changeover relay. At these connections, Pump is used to empty the filled tank. Pump starts emptying the tank when selector switch in closed position & float switch in uplift position making the relay’s ‘NC ‘ contact closed.
We can also use this circuit as a safety from dry run condition in which pump don’t operate until water level is above than the minimum desired level.
CIRCUIT:
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Circuit to empty the tank with 3 phase pump running on DOL Starter
In single phase circuit, Pump is directly controlled through changeover relay for float switch but in 3 phase, Pump should be controlled through contactor whose coil’s voltage is 230VAC. As described above.
SUMMARY
- Float switch is a type of switch that floats into the water. Which is used to control a pump or a valve.
- The float switch consists of hollow plastic chamber in which a limit switch is attached with mechanical lever.
- Changeover relay & mechanical lever arrangement are the key components in float switch. Entire working depend upon that two components.
- Changeover relay in float switch; is utilized to implement multiple circuits.
FAQ List:
Q1: What is a float switch?
A1: A float switch is a device used to automatically control the water level in a tank. It detects the water level and turns pumps or valves on or off to maintain a desired level.
Q2: How does a float switch work?
A2: A float switch has a buoyant float that rises and falls with the water level. When the water reaches a set height, the switch triggers a relay or circuit to turn the pump on or off.
Q3: Can a float switch prevent tank overflow?
A3: Yes. Float switches are commonly used to stop water pumps automatically when the tank is full, preventing overflow.
Q4: What are the types of float switches?
A4: Float switches can be mechanical, electronic, vertical, or horizontal, depending on installation and tank design.
Q5: How do I wire a float switch to a water pump?
A5: A float switch can be wired to the pump using a relay or directly if ratings match. Usually, it’s connected in series with the pump circuit for automatic operation.
Q6: Can I use a float switch for both high and low water protection?
A6: Yes. Installing two float switches—one for high-level (to stop the pump) and one for low-level (to start the pump)—is common practice.
Q7: What maintenance does a float switch require?
A7: Regular cleaning of the float, checking wiring and contacts for corrosion, and periodic testing are necessary to ensure proper operation.
Q8: Is it safe to install a float switch myself?
A8: Yes, if you follow the manufacturer’s instructions and ensure electrical connections are insulated and waterproof. For high-capacity pumps or complex setups, consulting a professional is recommended.
Q9: Where can I find a circuit diagram for a float switch setup?
A9: Circuit diagrams are available in the user manuals of float switches and online. Typically, they show the float switch connected to a relay that controls the pump.
Q10: Can a float switch be used for liquids other than water?
A10: Some float switches are designed only for clean water. For chemicals or corrosive liquids, you must use a switch made from compatible materials.
Hope, you like the post if you have any doubt, suggestion or query please do comments !