What are Float Switches?

Float Switches are liquid level sensors that use a float with a magnet to determine and detect the level of liquid present, or absent, in a vessel or tank. A float switch has one main purpose – to trigger an event when the liquid reaches a certain level such as a pump, by activating an alarm or another electronic device. 

Designed to measure depth, volume or other metrics within a tank or vessel, float switches are most commonly used to measure or control the flow of liquid in or out of a vessel. Float switches are flexible and reliable in that they can be customized from different materials to suit a range of environments and liquids, and they can be mounted vertically or horizontally. This leads on to the question: what is the difference between a vertical and a horizontal switch?

Vertical Float Switches

The most common level sensors in use, vertical float switches, hang or are mounted from the stem at a predetermined threshold at the top of the tank or vessel, or at the bottom and when the liquid reaches or reduces, to a certain level, the doughnut shaped float will rise or fall along the stem.

One or more glass reeds with two metal prongs are hermetically sealed inside the float. Magnets on the outside of the glass reed rise and fall with the position of the float connecting or disconnecting the metal prongs to either open or close the circuit switch inside the stem. Hanging vertically, the float switch is either in the “normally open” or “normally closed” position.

With “normally open” switches, the magnets bring the metal prongs together to complete the electrical circuit, activating any connected electronics for instance high-level alarms, bilge or other pumps.

“Normally closed” switches feature a completed electrical circuit when the device is in its prone position.  The rising liquid levels in the vessel move the magnets such that the connection is severed and the electrical circuit is disrupted for instance with an emergency tank shut off.

Horizontal Float Switches

Horizontal float switches are made of two components, the first is side-mounted through a hermetically sealed hole on the side of the vessel or tank. Attached to it, the second component, the float, hangs freely with the electrical circuit open. When the liquid within the vessel or tank rises high enough, the float rises and closes the circuit, sending an electrical signal through the attached wires to the outside of the tank, through the watertight seal, in turn activating a pump to reduce the liquid level for instance.

Choosing between Vertical and Horizontal Switches

When Should You Use a Vertical Float Switch?

  • Many heated or cryogenic vessels have jacketed walls making it difficult to install a sensor through the side of the vessel. This makes vertical float switches preferred for these applications. 
  • Vertical floats can be designed to be multi-point so if multiple levels are needed, it can be accomplished with one port in the top of the tank vs. multiple ports going up the side of the tank.

When Should You Use a Horizontal Float Switch?

  • Horizontal float switches are great when the top of a tank is inaccessible or hard to reach. They can be easier to install, maintain, route wires from, etc. 
  • Horizontal float switches are a better suited option when you have a tall tank that you want to measure liquid level at the bottom of. An ultra-long vertical float switch may not be practical – expensive to manufacture, expensive to ship, hard to install, etc. Whereas horizontal float switches are a much more affordable and practical solution.

What are Float Switches Used For?

Float switches are versatile and can be utilized in a number of different situations. Vertical float switches are often found in appliances such as dishwashers and add another layer of protection against overflow and flooding, monitoring the rising water levels in the event that the usual fill timer fails. They are also found in aquariums, HVAC, medical, marine uses, wastewater treatment, chemical processing, breweries and wineries and bioprocessing.

In the case of commercial vehicles and tractor trailers, float switches monitor how much fuel is present in a holding tank, allowing for proper operation and distribution. When the fluid levels or temperature changes within the vessel or tank, a signal is sent to activate an emergency alarm or stop switch, preventing equipment failure and in turn stopping an event like a serious oil spill for instance.

Many residential and commercial buildings, hospitals, factories and manufacturing enterprises rely on having back up generators in times of bad weather and power outage. Float switches form part of these essential pieces of equipment – maintaining a steady flow of fuel, preventing overflow and similarly low fuel, causing a shut off in an emergency situation.

Similarly, in bad weather conditions, many people rely on the use of sump pumps on their properties or business premises. Float switches attached to a pump can allow the user to leave the pump in place without the need to constantly monitor the water levels and turn the pump on and off manually. A float switch can monitor the water levels and automatically switch the pump on as the water rises and switch it off again as the water level falls. 

Wireless Float Switch Technology

Multilevel float switches can also be integrated with a wireless transmitter to offer a unique opportunity when it comes to controlling remote relays that signal an on or off function. The flexibility of float switches can be applied to several industries, providing cost effective and reliable data.

In agricultural monitoring, when a lack of liquid or moisture is detected by the sensor an irrigation system can be activated, preventing rot from overwatering of crops. Within the chemical processing industry, the handling, monitoring and maintenance of sensitive liquids and their containers can be aided by multilevel float switches. 

Wireless transmission of liquid level indication is also beneficial in the oil and gas processing industry. Less costly than hard wiring, these solutions can monitor tanks, compressors and wellheads in rugged terrains and in areas that pose risks and measure liquid levels, pressure, temperature, in real time.

Float Switches for Every Industry

Regardless of whether you’re using a horizontal float switch or a vertical float switch, special considerations need to be made to pick the right material, including:


  • Density of the liquid to be measured
  • Normally open vs. normally closed switches – which corresponds to the “fail-safe” condition?
  • Material compatibility
  • Size


At SMD, we can help find the right float switch for you, based on your unique needs. With the flexibility in materials and uses for both vertical and horizontal float switches, you can be sure that SMD Fluid Controls has a customisable solution for your requirements. Contact us today to discuss on (203) 294 5800 (US) or 01284 852000 (UK)