In the most basic sense, an electrical switch is a device that controls an electrical circuit by either opening or closing the loop. When a switch is in the on position the circuit is completed, and vice-versa.
This process can serve an almost infinite number of functions, depending on the specific use and other factors. For this reason switches can take on a number of different forms.
When it comes to vertical float switches, units are commonly referred to as “Normally Open” or “Normally Closed,” meaning that specific liquid levels close or sever the electrical circuit. In both cases, a glass reed is sealed inside the float switch’s stem, with magnets mounted in an external float.
Normally open switches have an open, or incomplete, circuit when the float is in the “normal” position. The “normal” position in most cases will mean that the float is suspended above the liquid line, not floating. When the liquid level rises, the float moves with it, bringing the magnets up and into a position where they attract and close the internal reed switch, completing the circuit.
Applications for normally open switches might include level regulation and high-level alarms.
In normally closed configurations the electrical circuit is closed, or completed, when the float is in its normal position. When the water rises and the float is lifted, it moves such that the reed switch is no longer held together by the magnets and the circuit is opened.
Potential applications for normally closed float switches are overfill shutoffs and level control.
Switches can also be mounted upside down, making normally open units into normally closed ones and vice-versa.
If you’d like a normally open or normally closed vertical float switch custom-configured for your specific design needs, contact SMD Fluid Controls to speak with their team of experienced engineers today.