Back to top

Using Displacer Switch Technology to Control Sump Liquid Level

Displacer switch technology is a popular level control solution across numerous process industries today. This is particularly true for sump level control, where displacer switches can provide a low cost, automated solution that is highly reliable because it is not affected by surface turbulence, foam or changes in specific gravity.

In this post, we will discuss the use of displacer switch technology to automatically control level and provide overfill protection – or a high-level alarm – in a sump. To learn how a displacer switch uses the principle of mechanical buoyancy to provide accurate level measurement, please read our previous blog post.

How Displacement Type Liquid Level Pump Control Works
Installing a displacer actuated pump control level switch, such as the Magnetrol® Series A10 displacer switch, is a proven way to maintain level between two set points automatically. The capability to automatically control the sump level in this manner makes a displacer switch an ideal overfill prevention solution.

The rate at which a sump pump fills depends upon system runoff. However, when the liquid level reaches the “Pump On” set point, the displacer level switch automatically actuates a sump pump to drain the liquid. Then, when the liquid level drops to the “Pump Off” set point, the displacer switch turns the sump pump off automatically. This allows level to begin rising again for the next pumping cycle.

You can calibrate the “Pump On” and “Pump Off” set points by clamping the displacer modules at the required on and off points. (It is best to complete this step before you lower the displacer assembly onto the sump.) As you increase the distance between the “Pump On” and “Pump Off” set points, you will also increase length of the pumping cycle.

It is important to note that surface turbulence will not cause rapid pump cycling. In fact, once the liquid level reaches the “Pump On” set point, the switch will not reverse until the liquid reaches the “Pump Off” set point.

In addition, when a displacer switch is set for the minimum specific gravity of any liquid that flows into the sump, the displacer unit will continue to cycle the pump with allowable changes in set points.


Follow Our Displacer Switch Discussion
Next week, we will examine how displacer switches can provide an effective liquid level control solution for steam boilers in the power generation industry. For more information about displacer switches, you can also download the MAGNETROL Buoyancy Products technology bulletin.