Magnetic level switches are simplest & most reliable instruments used in industrial level measurement.
Whether it is a water tank, chemical vessel, diesel storage tank, boiler, or sump, these switches silently monitor liquid levels and activate alarms or pumps when needed.
But how do these small devices perform such an important job with such high reliability?
In this article, we will learn how magnetic level switches work, why industries trust them, and what makes them one of the most low-maintenance level detection technologies.
Let us understand everything here.
What Is a Magnetic Level Switch?
A magnetic level switch is a device used to detect whether the liquid level inside a tank has reached a certain point. Instead of using electronics, complicated circuits, or external power, it works using magnets and a small component called a reed switch.
Because of this simple design, magnetic level switches are:
- Durable
- Safe
- Easy to install
- Able to work in harsh environments
No matter where you see liquid being stored or moved, there is a good chance a magnetic level switch is working quietly in the background.
The Two Main Parts of a Magnetic Level Switch
To understand how magnetic level switches work, let’s first look at their two key components.
1. The Float (With a Magnet Inside)
This float is placed inside the tank or along the side of the mounting tube.
It:
- Floats on the liquid surface
- Moves up and down as the liquid level changes
- Contains a strong permanent magnet
2. The Reed Switch (Inside the Stem/Tube)
The reed switch is a tiny electrical switch sealed inside a glass capsule.
It:
- Stays in a fixed position
- Is protected from the liquid
- Changes state (ON/OFF) when a magnet comes near it
These two parts work together without touching each other meaning no wear, no friction and very long service life.
How Do Magnetic Level Switches Work?
Here is the basic working idea:
The float rises and falls with the liquid level.
As the float moves, the internal magnet moves with it.
When the magnet comes close to the reed switch: The reed switch contacts either close or open.
This change generates an ON/OFF signal.
This signal can be used for: High-level alarm, Low-level alarm, Pump start/stop, Valve open/close, Safety interlocks
That’s it, no power supply, no moving mechanical contacts, no electronics.
This simplicity makes magnetic level switches one of the most reliable choices for level control.
Why Industries Trust Magnetic Level Switches
Magnetic switches may look simple, but they are engineered to survive very tough environments.
Here is why they’re so popular:
1. No External Power Required
The reed switch operates purely through magnetic force.
Perfect for remote or hazardous locations.
2. Extremely Reliable Switching
Reed switches are sealed in glass and protected from liquid or environmental damage.
They can last for millions of operations.
3. Works in Extreme Temperatures
Depending on design, they can handle:
- Very high temperature (boilers, hot oil tanks)
- Very low temperature (cryogenic applications)
4. Handles High Pressure Easily
The stem and construction are strong enough to work in high-pressure vessels.
5. Suitable for Almost Any Liquid
Magnetic level switches work with:
- Water
- Oil
- Chemicals
- Diesel
- Refrigerants
- Acids (with proper material selection)
6. Very Low Maintenance
No exposed electrical contacts mean no corrosion or wear.
7. Safe for Explosive Areas
Since the switching happens without sparks or open contacts, they are ideal for hazardous zones.
Where Are Magnetic Level Switches Used?
Magnetic level switches are used almost everywhere because they are simple, cost-effective, and reliable.
Common Applications:
- Water tanks
- Chemical process tanks
- Pump control in sump pits
- Boiler feedwater tanks
- Fuel and diesel storage tanks
- Coolant reservoirs
- Hydraulic oil tanks
- Sewage treatment plants
- Food & beverage tanks
- Pharmaceutical mixing vessels
Any process that needs high-level or low-level protection can use magnetic level switches.
Types of Magnetic Level Switch Configurations
There are several installation options depending on tank design and process conditions.
1. Top-Mounted Magnetic Level Switch
Mounted on tank top
Float moves along vertical stem
2. Side-Mounted Magnetic Level Switch
Mounted through a side nozzle
Switching happens horizontally
3. Multi-Level Magnetic Switch
Contains multiple reed switches
Provides more than one switching point
4. External Chamber / Bridle Type
Mounted on a chamber connected to tank and Ideal for high pressure or dirty fluids
Each configuration uses the same basic principle => float + magnet + reed switch.
Understanding Reed Switch Operation
Think of the reed switch as two thin metal strips sealed inside a glass tube. These strips don’t touch each other until a magnet comes close.
When the float magnet reaches the switch:
- The strips snap together → ON signal
- When the magnet moves away → strips separate → OFF signal
This operation is extremely fast, clean, and reliable.
Common Uses of Magnetic Level Switch ON/OFF Signals
A single magnetic switch can perform very important safety or control functions.
High-Level Alarm
Prevent tank overfilling
Low-Level Alarm
Protect pumps from dry running
Pump ON/OFF Control
Automatic pump control in sumps or reservoirs
Safety Interlocks
Shut down equipment when level is unsafe
Valve Operations
Open/close valves during filling or emptying cycles
Machine Protection
Prevent overheating or damage due to low coolant levels
These switches act as the “eyes” of the tank—always monitoring quietly.
Advantages of Magnetic Level Switches
Here is why they continue to be the preferred choice for many level applications:
- Simple design
- Low cost
- Long service life
- No calibration required
- No moving mechanical contact
- Works with conductive/non-conductive liquids
- Suitable for corrosive liquids with proper materials
- Excellent repeatability
- Can handle dirty liquids without sticking
Limitations of Magnetic Level Switches
Even though they are reliable, magnetic level switches are not ideal for:
- Very viscous liquids
- Liquids with heavy foam
- Very dirty or sludge-based fluids
- Applications requiring continuous level measurement
For such cases, technologies like radar, ultrasonic, or capacitance might be better options.
What we learn today?
Understanding how magnetic level switches work helps technicians, engineers, and students appreciate why these devices are so widely used in industry.
With just a float, a magnet, and a reed switch, these instruments offer:
- Accurate level detection
- Reliable ON/OFF switching
- Excellent durability
- Zero-power operation
- Safe performance in harsh conditions
Their elegant simplicity is the reason they have remained one of the most trusted level-sensing technologies for decades.