Switching Units for Pumps

Switching units ensure the control and, in some cases, the regulation of pump operation. A correctly chosen pressure switch, flow switch, or float switch not only ensures the proper functioning of the pump but also extends its lifespan, prevents dry running, and even reduces energy demands.

In the case of using domestic waterworks, self-priming and submersible pumps for wells and boreholes, the installation of a switching unit is necessary. This device ensures that when a draw-off point is opened – for example, a water tap – the pump starts immediately and maintains the required pressure. Similarly, when the draw-off is finished, the switch disconnects the pump. This also occurs in the event of dry running, which could damage the pump.

What are the types of switching units?

Pumps and domestic waterworks can be controlled in several ways. In our offer, you will find pressure, flow, combined, and float switches from manufacturers Grundfos and Wilo. Their use varies according to the following requirements and parameters:

• Switching unit combining pressure and flow switch

The most commonly sold and most comprehensive option in terms of pump control is a switch combining a flow and pressure sensor. When the tap is opened, the pressure first drops, and the switch turns on the pump. When the tap is closed, the second sensor detects the cessation of flow and turns off the pump before a higher pressure increase in the system occurs.

• Pressure switching unit

Standalone pressure switches are mainly used on waterworks sets, in combination with a pressure tank. They switch the pump to keep the pressure in the tank within a specified range. When water is drawn, the pressure drops, the switch detects the change, and turns on the pump. When water draw-off is finished, the pump runs until the pressure in the tank reaches the desired value again. In practice, pumping is usually controlled by thirds of the pressure tank volume. Before starting the draw-off, the pressure tank is ⅔ full, and the pump is off. When the tap is opened, water starts to flow, but the pump only restarts when the switching unit detects a drop below ⅓ of the volume. The pump runs until it refills to ⅔ of the volume.

• Flow switching unit

Flow switching units are mainly used in waterworks where only a hose is thrown into the well, and it is not possible to install a float sensor. Therefore, the flow is monitored directly at the pump. The function of starting the pump is then similar to that of a switching unit combining flow and pressure sensors.

• Float switching unit

Float switching units are mainly used with submersible pumps, where they are placed directly on the pump, which they turn off in case of water shortage. Float switches are therefore suitable exclusively as protection against dry running.

How to choose switching units?

The correct choice of switching unit is primarily guided by:

• Type of use,
• Maximum flow rate,
• Switching pressure: it can be fixed, but in most products, it is adjustable,
• Equipped with dry run protection and automatic restart,
• Equipped with a check valve,
• Equipped with a frequency converter,
• Installation method (horizontal, vertical), connection size.

Do switching units offer additional functions?

A common feature is built-in dry run protection, where after a certain time, the unit activates the automatic restart function. Advanced control units can maintain constant pressure thanks to smooth speed regulation using a frequency converter. They can also delay the pump shutdown to prevent cycling, and they include motor current protection.
Additionally, selected products allow setting the on and off pressure. A clear display combined with LED indicators informs about the current operating status and ongoing activity. For better pump protection, a possible leakage sensor is also available. Some switches are also equipped with a manometer.

Is there a way to prevent pump cycling?

In the case of minor leaks in the piping or other negligible pressure losses, installing a flow switch Wilo BRIO 2000 TANK equipped with a 0.4-litre pressure tank may be the solution. Thanks to this application, which is particularly suitable for domestic waterworks, it is possible to prevent cycling (repeated unwanted pump starts) and thus extend its lifespan.

How to install a switching unit?

Installation is not difficult, and the package includes instructions in Czech. Usually, it is enough to connect the power cable, which is part of the switching unit, and connect the switch to the water pipe at any location between the pump itself and the first draw-off point. The operation of these units is generally completely silent, and depending on the purpose and construction method, they are often equipped with an integrated check valve.