Float switches are basic devices used to monitor and control liquid levels in tanks, pits, and other vessels. They are widely used in residential, commercial, and industrial applications to control the flow of water, chemicals, and other fluids. In a simple liquid level control application, the switches can be used to start or stop pumps, activate alarms, or turn other systems on or off.
How It Works
Float switches operate based on the float's buoyancy. As the liquid level rises, the float floats up. As the liquid recedes, it pulls the float down. Depending on the position of the float, the switch inside is a magnet or a small sensor that turns the switch on or off. Float switches can be made of mechanical components, or they can use magnets and sealed sensors.
Different Types of Float Switches
There are various types and styles of float switches. Each one is built for different applications and configurations.
1. Mechanical Lever Float
This type has a float connected to a small arm as the float moves up and down with the liquid level, the arm pivots. The arm then pushes a switch to either switch something on or off.
2. Magnetic Reed Float
There is a magnet that is included inside the float of this design. The float moves up and down a rod, activating a sealed switch inside with a magnet. This type has no touching components, so it lasts longer and doesn’t wear out quickly.
3. Cable Float (Weighted)
This float is suspended on a flexible cable and can move freely. A weight holds the cable fixed. As the float moves with the rising or falling liquid, it tilts and changes its angle, turning the switch on or off. This type would be suitable for deep tanks or wells.
4. Dual-Level or Two-Stage Float
These switches consist of two levels. The second float activates the pump or device under normal conditions. The second float serves as a backup to trigger an alarm if the liquid rises too high or falls too low. It adds extra safety.
Common Uses
Float switches serve a wide variety of locations to control or monitor liquids. They are used for many things, some of which are:
- Used in basements to activate pumps to run when water is high and to stop them when water is low.
- Assist in maintaining water levels within a safe range.
- Pump treatments at mixing plants.
- To pick up dangerous liquids.
- Use food safe materials to keep equipment clean.
- Switch off the pump when the liquid is too low to prevent it from running dry.
Benefits of Float Switches
Float switches are useful because they are easy and dependable. Here are a few advantages:
- Easy to Use: They have minimalistic designs, and they don’t require much training to install or use.
- Reliable: They usually run trouble-free for a long time because they have few moving parts.
- Affordable: These switches are cheaper than most electronic sensors.
- Works with Many Liquids: They are constructed of materials that can resist water, oils, chemicals, etc.
- Adjustable Settings: Some models allow users to configure the points at which the switch automatically turns on or off.
- Flexible Design: They can be mounted from the top, side, or bottom depending on the tank or setup.
Choosing the Right Float Switch
Selecting a correct float switch relies on a few key considerations:
1. Fluid Compatibility
A variety of liquids will have unique elements. Float and switch materials must be compatible with the liquid types so as not to cause damage. Some switches, for instance, are designed for water, while others are designed for oil or chemicals.
2. Liquid Density
Some liquids are less dense than water, and some are more dense than water. Ensure the float is free to rise in the liquid. Fewer floats may be needed for lighter liquids.
3. Temperature and Pressure
It has to tolerate the heat and pressure of the system. If the tank will be hot or under pressure, select a float switch that is designed for those circumstances.
4. Mounting Style
There are several ways of installing float switches. Side-mounted switches are set at a specific level. Some are top-mounted and can span a series. Cable floats (strung at the top) are easy to use for deep or narrow tanks.
5. Electrical Needs
If using a switch, ensure that it has the appropriate voltage and current rating for the pump or control system. It should also be verified if it should be NO or NC.
6. Protection Rating
Other switches must be impervious to dust, water, or chemicals. Check for an IP rating, including ratings of IP67 or IP68, or NEMA 4X/6 for harsh conditions.
Installation Tips
A well-done installation will allow the switch to perform better and last longer.
- Securely mount the switch so it can’t shift or vibrate.
- Avoid positioning the float in or near water inlets or outlets, where liquid moves around.
- Give the float some room to move and adjust the height.
- The weatherproof connectors essentially provide a way to open the signal.
- Make sure the float cannot impede anything else in the tank.
Maintenance Tips
Float switches must be regularly checked to ensure they remain in good condition.
- Check for cracks, corrosion or other damage.
- Clear any slime, buildup, or dirt that may inhibit the float.
- Test the switch with a multimeter or manually raise the float.
- Keep the switch housing waterproof.
- If the float or switch isn’t functioning properly, replace it or it may cause bigger problems.
Standards and Safety Certifications
Reliable float switches abide by some safety regulations to ensure performance under all circumstances.
- IP Ratings (IEC 60529): These indicate how well the switch is sealed against dust and water. IP67, for instance, means it can be under water for a short time.
- NEMA Ratings: Used in the U.S., for example, NEMA 4X is safe for corrosive environments or outdoor use.
- UL and CSA: These safety marks indicate that the switch has passed electrical safety tests in the U.S. and Canada.
- ATEX and IECEx: These are required in explosive gas, and explosive dust areas. They prevent the switch from sparking or catching fire.
Conclusion
Float switches are also a highly reliable method for controlling and monitoring liquid levels across many industries. They are low-cost, simple, and easy to install. Whether in a small water tank or a large industrial system, the proper float switch prevents spills, protects equipment, and allows systems to operate safely. When correctly selected, installed, and cared for, float switches deliver extended and reliable performance.