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Due to its reliability, a float switch is one of the most frequently used measurement technologies for monitoring liquid media levels. Its simple yet effective design consists of a hollow float within a guide tube, rising and falling with liquid levels and activating switches along the way. Find out more about what a float switch is and how it works.

A float switch is versatile, consistent and exceptionally reliable. Its simple mechanics have been used to control water flows in mills and fields for centuries. Despite various level-measurement innovations in the past decades, the modern float switch is still the most frequently used method for monitoring liquid media levels today.

In its simplest form, a float switch consists of a hollow float body with a built-in magnet, a guide tube to guide the float, adjusting collars to limit the movement of the float, and an inert gas switch contact on the inside. See this short videofor a visual representation of level monitoring with a float switch.

How Does a Float Switch Work?


The buoyant float with a permanent magnet rises or falls along a guide tube with the rising or falling levels of the medium being measured. The guide tube is fitted with a reed contact, which is energized by the movement of the magnet. When a preset switch point is reached, the reed contact is actuated.

The guide tube’s reed contacts consist of contact leaves within the hermetically sealed glass body. These move together or apart when a magnetic field is applied from the float. When a reed contact has a normally open function, the leaves are brought into contact when a magnetic field is applied. When the contact between the leaves is made, a current flows through the closed leaves and a switching signal is detected.

For a float switch with a normally closed switching function (SPST, or single-pole single-throw), the contact or circuit is interrupted when a magnetic field is applied. If one selects a change-over contact (SPDT, or single-pole double-throw), the glass body contains three contact leaves where, at all times, normally closed and normally open contact are simultaneously made for every operation.

Since the contact leaves are under a mechanical preload, a magnetic field must be applied for the contact leaves to close or open. This generates the desired switching signal (monostability). The adjusting collars serve as a limitation for the float body in the correct position, to ensure the desired switching signal is accurate in reaching the defined level.

WIKA: A Leading Provider of Float Switches

The simple and proven functional principle of a float switch enables a very wide range of applications, from general industrial systems to maritime vessels. One of WIKA’s most versatile float switches is the Model WFS.Its operation is non-contact and free from wear. It works independently of foaming, conductivity, dielectric, pressure, vacuum, temperature, vapors, condensation, bubble formation, boiling effects, and vibrations – making it a cost-efficient, simple solution suitable for almost all liquid media and many industrial applications.

As a leading provider of float-based measurement solutions, WIKA USA has options for many application-specific requirements. For more information, contact a WIKA experttoday.



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