We can come across many applications where it is required to either fill or empty a water tank with a pump. In these cases, it is important to avoid air or gas inside the pipe in order to protect the pump. This task can be automated with a float switch, a type of level sensor, more precisely a level switch that is designed to float on the surface of a liquid.

What is a float switch?

A level switch can be electronic or mechanical, but it serves only one purpose – to alert you if it detects the presence of the product so you can take action based on this alert. A float switch is one that does this while floating on the water or other liquid in the tank. Makes sense, right?

This article will explain why a float switch can be a better option compared to other level sensors or switches in a water tank. We will also tell you the main things you need to be aware of before replacing a float switch.

To know more about some other low-cost level transmitters in the market, you can read the Visaya Article here

Endress+Hauser
Liquifloat FTS20 The float switch for point level detection in liquids
in the shop from 56 €
FTS20

The advantages of a float switch

Using a float switch with a pump might damage the device. These devices are relatively fragile and even a little mishandling can render them out of service. However, we still recommend them using them. Here’s why.

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 measurement 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.

Choosing the right float switch

Having settled on a float switch for your application is only half of the work. You will also have to choose the right one from all the options available, based on the following specifications.

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.

changeover contact AC/DC diagram

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.

float switch cable length diagram
Example of FTS20 installation

Example:

For example, if we have a pump with a changeover connection of 3 wires, 230 V 50 Hz, it will certainly need a float switch so as to avoid it from flowing without any fluid. Here, the media is a soap solution at 25 degree Celsius.

In such a situation, we can use the FTS20 AC/DC version with a PVC cable. The AC/DC version works perfectly with 230V and the PVC cable is a safe choice for material compatibility.

Conclusion

The primary things to consider for selecting the right float switch includes appropriate cable length, the perfect material to be used and ensuring to have the right connection. Once we have answered these questions, it will be easy to select the right float switch based on the application required.

To know more about float switches and help you choose the right device, you can get in touch with our engineers and we will be happy to help.

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