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1. Industrial wastewater systems (like lift stations and sump pits) rely on float switches to control pumps and prevent overflows. Float switches automatically detect liquid level and turn pumps or alarms on or off.
We take calls on our float switches here at Sump Alarm. People often have questions about choosing, using, and fixing float switches. From those calls, we’ve compiled the top 10 frequently asked questions (with answers) about float switches in industrial wastewater applications. This includes common purchasing questions and troubleshooting pain points and related questions.
A float switch closes or opens an electrical circuit. Generally, this is done by the float switch changing its orientation. The name can be deceiving. Nothing special happens when the float switch “floats”. A more accurate name would be a “tilt switch”, but in the case of a “float switch” They are generally held in place by a fixed point on the cord. The fixed point may be somewhere the cord is anchored, it could be a cable weight, or some float switches (such as the SludgeBoss®) are “internally counterweighted” meaning they rotate around themselves. There are several different operators internal to the float switch that can be used. At Sump Alarm, our float switches contain a steel ball. There are some that contain mercury (now banned in some states, including California, etc.). When the float switch is lifted by water above the anchor point the ball (or mercury) will roll down to a point where it connects the electrical circuit.
When the electrical circuit is closed, the float switch generally triggers a pump to turn on (to empty or fill a tank or vessel). Essentially, the float switch serves as an automatic on/off switch for pumps or alarms, responding to changing water levels
Generally, in these applications there are multiple float switches deployed, and most systems use a “3 float system”. For example, if the application is to keep the tank or vessel empty, the top float switch would trigger an alarm that something is wrong (i.e. the fluid level is higher than it ever should be). The next float switch down from the alarm float switch starts the pump, and the bottom float switch turns the pump off. Having a substantial distance between the two allows the pump to run longer and start and stop less.
If the goal is to keep the system full, the float switch stack is inverted. The bottom float switch will alarm that the tank is below the minimum level. In a filling system, all the floats will activate (i.e. close the circuit) when they are in the down position. The next float up triggers the pump to turn on and fill the tank. When the top float switch raises, it turns off the pump.
A relay is required for either one of these multiple float switch circuits. This is called a “latching circuit”. Once the relay is triggered to “run the pump”, the relay stays latched until the second float switch breaks the latch, which turns the pump off.
For more information on “latching circuits”, see the blog post here.