When liquid level switches are used in high-reliability applications, such as aircraft, submarines, nuclear power plants and medical equipment, it is essential that they operate with precision and dependability. Therefore, great care must be taken in choosing the best switch to fit each specific application. With many choices available in terms of switch style, size and material, knowledge of several scientific principles related to fluids is valuable during the float switch selection process. Click here to download this Level Advice as a printable PDF file (120k).

One of the most common level-sensing switches used in industrial applications is the float switch. It consists of a float holding a magnet and a dry reed switch encapsulated within a stem. As the float follows the level of liquid in the vessel, the magnet also moves up and down. The magnet activates the reed switch when they're both at the same level, providing an "on" or "off" signal. The signal can be conditioned to activate alarms and controllers or complete a circuit that turns on pumps to fill a tank.

Before specifying a float switch, the customer must know the fluid being monitored. Characteristics of the liquid such as its turbulence, specific gravity, temperature and viscosity usually dictate essential switch characteristics.The liquid could also be a strong acid or base, which would influence material selection.

In industrial applications, turbulence can interfere with proper float switch operation. Turbulence can be caused by a vibrating tank, mixer agitation, boiling liquids or surging of liquid while the tank is being filled. A slosh shield can be used as a very low-cost and reliable solution. It isolates the switch from fluid motion and has holes to let air and water flow in and out.

Buoyancy, the tendency of a body to float or rise when submerged in a fluid, comes into play when a float switch is almost the same size as the vessel. The float will displace the liquid, so less liquid could actually be in the vessel than would be indicated by the switch. Miniature and subminiature switches minimize this possibility in small vessels.

Specific gravity is the ratio of the density of a material to the density of water. Materials that are lighter than water (having a specific gravity less than 1.0) will float in water, while those with specific gravities greater than 1.0 will sink in water.

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Contact Madison today to learn more about our liquid level float switch offerings!