Understanding the Float Switch: A Comprehensive Guide

By Clyde A. Sasquatch

July 1, 2024

Welcome to our ultimate survival guide to the world of float switches! I'll discuss float switches and their functionalities, pros and cons to each, common applications, and issues that could arise. My goal is to help you decide which will work best for you out in the wild.

What are Float Switches?

A float switch is a type of sensor that provides a way to automatically manage fluid levels in a tank or container by detecting the liquid level inside the tank. Float switches are commonly used in applications such as water tanks and sump pumps. They are key instruments in various industrial processes to prevent overflow, to prevent dry running, and to maintain desired liquid levels.

How Does a Float Switch Work?

A mechanical float switch includes a mechanism to operate by opening or closing contacts. As the liquid level rises or falls, the float moves accordingly. This movement triggers the switch to open or close an electrical circuit. Depending on the configuration, the float switch can either start or stop a pump, sound an alarm, or activate another control mechanism.

Float Switch Types

There are several types of float switches, each designed for specific applications and environments. Below are some of the most common types:

1. Standard or Tilt Float Switches

Standard or tilt float switches, also known as cable-suspended float switches, are tethered to a flexible cable and can be mounted using various kits such as the Standard Side Mount Kit, Wide Side Mount Kit, Adjustable Side Mount Kit, or Tire Tank Mount Kit. Tethering a float switch means attaching it to a fixed point within a tank or container, allowing it to float freely within a specific range. This setup allows the switch to move and tilt as the liquid level changes, triggering the switch at predetermined high or low points. These switches are versatile and can be used in a variety of water and sewage applications.

Pros:

• Flexible installation
• Suitable for turbulent conditions

Cons:

• May require more space
• Cable wear over time

Considerations When Selecting a Standard or Tilt Float Switch

Normally Open vs. Normally Closed

When selecting a float switch, it's important to consider its configuration and specifications. Float switches can be configured as normally open (NO) or normally closed (NC). A normally open switch remains open until the float reaches a certain level, at which point it closes the circuit. This type of float switch is active in the raised position and inactive in the lowered position. Conversely, a normally closed switch remains closed until the float reaches the predetermined level, which then opens the circuit. In this scenario, the switch will be inactive in the raised position and active in the lowered position.

Normally open switches are typically used in pump-down and high-level alarm applications, whereas normally closed switches are used in applications such as filling tanks or monitoring for low water level conditions. 

Wide-Angle vs. Narrow-Angle

Another important consideration is the operation angle of the float switch. Float switches can be designed with a narrow or wide operation angle, affecting their sensitivity and range of motion. Narrow-angle float switches have a smaller range of motion and are ideal for applications requiring precise level control, while wide-angle switches allow for more movement and are suitable for applications where more tolerance is acceptable. In a simplex or duplex pump application, three or four narrow-angle floats are generally installed in the sump area.

Cord Length

The cord length of the float switch is crucial, as it needs to be long enough to accommodate both the depth of the tank or container (while allowing the float to move freely) and the location of the pump control panel or power source. Choosing the correct cord length ensures proper functionality and prevents damage to the switch.

Learn more about the Float Pro® Control Switch!

2. Vertical Float Switches

Vertical float switches are installed vertically in a tank. They consist of a central rod with a circular-shaped float attached to it. The float moves up and down along the central rod as the liquid level changes. These switches can be configured to open or close a circuit at specific levels. They are often used in applications where space is limited, as they require less horizontal space than other types.

Pros:

• Space-efficient design
• Suitable for narrow tanks

Cons:

• May require a guide rod
• Can be more complex to install

3. Horizontal Float Switches

Horizontal float switches are mounted on the side of a tank. The float pivots on a hinge, moving up and down with the liquid level. When the float reaches a certain point, it triggers the switch. These switches are ideal for tanks with wider dimensions.

Pros:

• Simple installation
• Effective for wide tanks

Cons:

• Requires space on the tank's side
• Float may be affected by turbulence

4. Miniature Float Switches

Miniature float switches are compact and designed for small tanks or containers. They work similarly to other float switches but are much smaller, making them ideal for applications where space is extremely limited.

Pros:

• Compact size
• Ideal for small tanks

Cons:

• Limited switching capacity
• May not be suitable for high-pressure applications

Choosing the Right Float Switch

When selecting a float switch, it’s important to consider the specific requirements of your application. Factors such as the type of liquid, tank size, operating environment, and required switching capacity will influence your decision. Additionally, it’s important to ensure that the float switch is made from materials compatible with the process media to prevent corrosion or damage. Furthermore, considering the amp rating of the float switch is crucial. Control duty floats typically have a maximum amp rating of 5 amps, while pump duty floats have an amp rating of 13-15 amps, with a lock amp rotor rating of 50-96 amps. This ensures that the float switch can handle the electrical load without causing damage to the system.

Float Switch Applications

Pump Controls

One of the most common applications of float switches is in pump control systems. Float switches regulate the operation of pumps by monitoring liquid levels in tanks, sumps, or reservoirs. A float switch can be connected directly to the pump as a pump controller, or it can be wired to a control panel as a pump switch. There are often several switches connected to the same control panel, depending on the application. 

When the liquid reaches a certain level, the float switch either activates or deactivates the pump. This automation prevents the pump from running dry, which can cause damage to the pump, and helps maintain the desired liquid level. For instance, in a water tank, a float switch can turn off the pump when the tank is full and turn it on when the water level drops, ensuring a consistent water supply. Note: Control switches are designed to carry lower amps than pump switches. They should not be used to carry the full load current of a pump.

Liquid Level Alarms

Float switches are also used as liquid level alarms. In this application, the float switch monitors the liquid level and triggers an alarm when it reaches a critical point.

Sewage Treatment and Lift Stations

Float switches are critical in managing waste levels in sewage treatment plants or lift stations. They are used to monitor and control the levels of sewage in various tanks and reservoirs. By automating the pumping process, float switches help maintain optimal levels in holding tanks, preventing overflows and ensuring efficient treatment of sewage. These switches can also trigger alarms to notify operators of high or low levels, facilitating timely maintenance and intervention.

HVAC Systems

Heating, Ventilation, and Air Conditioning (HVAC) systems often incorporate float switches to manage condensate levels. 

Marine Applications

Float switches are widely used in marine applications, such as bilge pump systems on boats and ships. 

Agricultural Irrigation

In agriculture, float switches are employed to control irrigation systems. They ensure that water tanks and reservoirs maintain appropriate levels to supply irrigation systems continuously. 

Fish Farming

Aquaculture or fish farming relies heavily on float switches to maintain optimal water levels in fish tanks and ponds. These switches help automate the water management process, ensuring a stable environment for fish and other aquatic organisms. 

Chemical Processing

In the chemical processing industry, maintaining precise liquid levels is critical to ensuring safe and efficient operations. Float switches are used to monitor and control the levels of various chemicals in storage tanks and reactors. 

Food and Beverage Industry

The food and beverage industry uses float switches in various processes to maintain hygiene and efficiency. For instance, in dairy processing, float switches monitor milk levels in storage tanks to ensure continuous production and prevent spillage.

Environmental Monitoring

Environmental monitoring systems use float switches to track and manage water levels in natural and artificial bodies of water. For example, float switches monitor river and reservoir levels in flood management systems, providing data to predict and prevent flooding. 

Oil and Gas Industry

In the oil and gas industry, float switches are used to monitor and control the levels of various fluids, including crude oil, refined products, and wastewater. These switches help automate the filling and emptying processes in storage tanks, pipelines, and processing units. 

Common Issues and Solutions

• A float switch, while generally very reliable, can fail or go bad due to incorrect material choices, physical damage, or improper use.
• Physical damage to the float and/or shaft could impede the float’s movement and prevent the float switch from functioning correctly.
• Accumulation of debris, sediment, or other contaminants in the tank can also interfere with the movement of the float.
• Float switches require proper installation.
• Float switches are not for every application. In some scenarios, a pressure transducer or a radar sensor may be more suitable for the job. For a complete breakdown of the different types of level sensors for a variety of applications, click here for a comparison chart of additional types of level sensors.
• It is important to keep replacement float switches in stock for timely maintenance and troubleshooting.

Conclusion

Float switches are essential components in many liquid level control systems. Understanding the different types and their applications will help you select the right float switch for the application, ensuring reliable and efficient operation at your job site. Whether the job needs a switch for a simple water tank or a complex industrial process, there are a variety of different float configurations available. With this newfound knowledge, you are now better equipped to make an informed decision about the appropriate float switch for your application, and you're one step closer to becoming an insightful forest-dweller of Clyde’s Corner!

References

• Float Pro Control Switch Product Page, See Water, Inc., Accessed June 27, 2024
• Sensor Pro Series Comparison Chart, See Water, Inc., Accessed June 27, 2024