What is a float switch?

Categories: Technical

What is a float switch?

A float switch is a small device enclosed in a waterproof case used to turn a pump on and off relative to the water level in the tank. It can be attached to a submersible pump or a pump that sits outside the tank and it protects the pump from running if the water is low.

Advantages of float switch

Float switches are cheap

The main advantage of a float switch, which makes it one of the most popular options for liquid level measurement, is the low cost. Other, more complicated methods of level measurement, like conductive, capacitive, and pressure, certainly last longer, but they are also much more expensive.

Easy installation and versatility

Compared to other devices available in the market, it is pretty easy to install a float switch. It is so simple in fact that it is a stretch to call it installation: you just need to put the float switch into the tank, make sure that the cable is long enough that the device can travel up and down the tank as the level of liquid rises and ebbs, and that’s it.

In some cases, installing other level measurement devices might require moving the pump, which is significantly more difficult. A float switch can be installed relatively quickly by one person.

A simple solution for simple problems

Different types of measurements require different devices. One of the most common types of level measurement applications involves a storage tank of non-corrosive liquid (for example, water, the most common liquid substance on our planet), at ambient temperature. Float switches excel in these applications, providing reliable measurements for a long time, with minimal installation and maintenance required.

How can we choose a good float switch?

·  The electrical connection between the float switch and the pump

In most of the cases where a pump is used, the pump has a changeover contact with 3 wires. Here, we must ensure that the float switch we acquire has the same connection so that it can stop the pump when the water goes below the desired levels.

Furthermore, the current between the float switch and pump must match as well. This means that they must have the same specification. For example, if the pump works with 24 V, 220 V and/or needs an ATEX approval, the float switch must also be compatible with this value.

·  Choosing the right material to avoid corrosion

Selecting the appropriate material is one of the main criteria while fixing on the right float switch. In cases where the liquid that we want to pump is water, corrosion is not a major issue. But, in the case of a solution, it becomes important to analyze the compatibility of materials. PVC is very versatile and usually a good choice, but considering the other compatible materials is also vital.

·  Cable length and liquid level

It is not a problem if the cable is too long. We can either cut it or roll it to adjust the size. The problem arises if the cable is shorter in length, we need to make a junction in order to let the cable reach the desired level. Also, since making a junction is more expensive than buying a new float switch, it is advisable to be mindful of the length of the cable.

Where is a float switch installed?

Horizontal HVAC units are often equipped with a drip pan, which is placed underneath the unit to prevent small amounts of excess condensate water from causing damage. However, in the event of a major leak, a drip pan can only hold so much before it overflows. A float switch installed on the drip pan could prevent such a situation from causing major damage.

For a vertical HVAC unit or horizontal unit without a drip pan, a float switch can be installed on the unit’s PVC drain pipe and will activate if water flow is obstructed. An HVAC unit may also come equipped with a condensate pump, which actively pumps excess condensation away from the unit instead of passively relying on gravity to drain it away. Such a pump also includes a float switch-like mechanism which works in the same way, disabling the HVAC unit and preventing the occurrence of major water damage.