How Does A Float Switch Work?

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A float switch is a device that contains a switch that opens or closes according to a liquids’ level. The float switch moves up and down with the liquid and activates when the liquid passes a certain threshold.

Float switches are used to detect if a liquid rises or falls above a specific level and send a signal to the rest of the system or activate a device. They are often used to control pumps, motors, valves, and alarms in various residential and industrial applications. Float switches are a popular choice for controlling liquid levels because they are reliable, cost-effective, and they can be used in many different liquids. 

How Do Float Switches Work?

Most float switches use a magnet which triggers a reed switch.  On a stem mounted float switch the magnet is contained in the floating portion while the reed switch resides in the main body. This allows the reed switch to be triggered without needing any direct physical connection between the floating portion and the switch. Such designs allow for the floating portion to move freely without getting stuck and doesn’t require waterproofing any moving linkages. 

On a cable mounted float switch the magnet and switch reside in the same waterproof body. The body floats on the surface while the cable pulls the body up or down. The magnet falls towards or away from the switch depending on the angle of the body, which changes with the liquids level. This design can also use a counterweight to pull the cable down at different lengths, which allows one to set the level at which the switch actuates. They also tend to have greater hysteresis (additional change needed to turn the switch off after it was turned on).

External Counterweight

When the reed switch closes it allows current to flow through, which can be used to either trigger control systems or turn on electrical devices directly. It is important to note that float switches have a maximum switching current and voltage, so be sure to read the manufacturer’s guidelines to not exceed this specification. 

How To Wire A Float Switch?

Float switches come in two wiring configurations; normally open and normally closed.

Normally Open (NO) float switches are open when the liquid is below their activation threshold, meaning their electrical switch is disengaged and doesn’t conduct current. This is useful when you want to turn something on when the liquid reaches the float switch.

Normally Closed (NC) float switches are closed when the liquid is below their activation threshold, meaning their electrical switch is engaged and conducts current.  This is useful when you want something to stay on until the liquid reaches the float switch, or to turn something on when the liquid falls below the switch.

Float Switch Applications

As float switches come in a variety of types and designs, they can be used for a wide variety of applications. The most common applications include the following:

  • Sump and sewage pits: Float switches are used to detect and operate pumps to prevent the water from rising into the pits.
  • Potable water, surface water, wastewater, and sewage systems: Plastic float switches are used for highly corrosive applications.
  • Refrigerators and air conditioning units to control water levels.
  • Beverage and food industries to control the in and outflow of liquids: Stainless-steel float switches are used for food or drinking water applications.
  • Industrial washers to monitor the water level. 

Summing Up, Float Switches

Float switches will provide you with an accurate, reliable, simple, and low cost way to measure liquid levels at a single point and activate devices in response to changing liquid levels. 

Float switches come in a variety of shapes, materials, and wiring schemes to fit any liquid monitoring applications.

If you have any questions regarding float switches or are unsure which float switch is for you, please do not hesitate to contact our world-class team at Atlas Scientific.

Float Switches

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