Float Switches

A float switch, also known as a float sensor, works much like a standard light switch, they open and close contacts to control whether or not signal current can pass through. They are either Normally Closed, meaning current is flowing, or Normally Open, meaning the current is not flowing. The “Normal” state is when the float switch is down, resting on its cable or float stop.

In other words, a float switch considers an empty state normal (no liquid to lift the float). A Normally Closed float switch in an empty tank would have current flowing through it, activating whatever process it is supposed to - such as turning on a pump or sounding an alarm. A Normally Open float switch, on the other hand, would break the current in an empty tank, and would not close, or activate, until the tank was full enough to lift the float.

A float switch is pretty straightforward, without many bells or whistles. However, there are several reasons why ours stand out. Most impressively, the Kari cable-suspended float switch can have a single switch point, or up to four, all-in-one float. This is unheard of amongst competitor float switches. These float switches are set up for various different applications, like fill control or empty control with an isolated alarm.

Our stem-mounted float switches can have up to seven floats - each with one switch. These are custom placed according to your application needs. They can operate in temperatures up to 212° F (100° C). Unlike a cable-suspended float switch, these don’t need a wide area to operate. They’ll work anywhere large enough to fit the sensor.

Our miniature float switches are a versatile group, some capable of operating in temperatures up to 392° F (200° C). The small float switch is very compact and perfect for small tanks.

Point-level sensors in general are great for controlling pumps and alarms when a liquid level must be maintained within a certain window of acceptance. A great example is pump control. If tanks get too full, there are two risks: overflow, and if filled from the bottom, pump failure. If a tank gets too low, you risk pump failure as well. Having a level float switch is a great method for turning pumps on and off.

Some level float switches need a controller to add logic to this on/off equation. If a pump is controlled directly by a switch with no logic, and the liquid level has stopped right at the float (like it’s designed to do), any ripple at the surface will cause the float to bounce up and down, chattering between on and off. This would burn a motor out quickly.

The control adds hysteresis, which tells the pump not to chatter, but to turn off at one level, and turn on only at another level. If you’re filling a tank, for example, the top float would tell the pump to turn off. The pump would stay off until the tank had emptied to the level of the bottom float, where it would turn on - staying on until it reached the high level once again.

Some float switches, like our Kari line, have hysteresis built in. These level float switches have multiple (up to four) switch points in a single float. This float switch is designed with a mechanical hysteresis for different applications, such as tank fill or empty, which controls which switch point is for on and which is for off. Some switch points are designed to handle alarm configurations as well.

Finally, many level float switches are used simply for level indication. Some applications call for a series of lights that indicate something like 25, 50, 75, and 100 percent full. It’s not continuous level measurement, but it’s close.

Food Service Industry is a great place for APG's FS Miniature Stainless Steel Float Switches. All three Series--the FS-400, FS-410, and FS-500--carry NSF 169 certification for food-adjacent equipment and can handle temperatures up to 500°F. So they can be used in steamer reservoirs, commercial dishwashers and fryers, and ovens.

APG's FL Series of Stem-Mounted Float Switches are a good fit for small or large batch chemical handling and storage. With lengths as short as 6 inches and as long as 12.75 feet, an FLE, FLR, or FLX can be used in anything from small totes to process reservoirs and large storage tanks. Since each FL is custom-made to your specifications, you can set as many as seven level alarms at the precise points you need.

While a miniature float switch and stem-mounted float switch can easily be nestled into tight spaces, cable-suspended float switches need space to move with the changing liquid level. Thus, unless they are tethered for a minimum distance between switching levels, APG's Kari and TLS Series Cable-Suspended Float Switches only make sense in medium and larger applications. Whether you have an industrial process that requires a large amount of water, or you are a small commercial entity with your own well or water tank, a cable-suspended float switch will make sure you are never surprised by a lack of water.

•    Do you have a simple mechanical float switch?
•    Can your float switches work in hazardous locations?
•    How can I use fewer cable suspended float switches?
•    Can your float switches withstand high temperatures?
•    Can I change the NO/NC state?
•    Can the MLS switch point be adjusted?
•    Can your float switches be used in a pressurized tank?