The term dry-run, strictly speaking, is when the pump is being operated with no liquid within the pump casing. The result is rapid overheating of the pump interior caused by friction between stationary and moving parts. Dry-running almost always results in pump failure if not detected and remedied quickly. Similar features of overheating can also happen when the pump is insufficiently cooled, such as shut-off valve, improper priming, air entering the pump from the suction system, vaporizing of the chemical under severe cavitation, etc. While these causes are not technically dry-running, it is often described as having the features of dry-running.

The common observable feature of dry-running and other failure modes that result in the pump over-heating is either no flow output or significantly reduced output. From this reasoning, we can easily detect such operating conditions by monitoring the output flow capacity of the pump by sending digital flow meter readings to the control station or the PLC.

In many industries, digital flow meters are not commonly installed due to their relatively high costs. However, since the flow output (loading) of the pump is low, the amount of energy required to rotate the pump is also reduced. We can use this feature to indirectly detect potential dry-running and similar failure modes by monitoring the loading of the motor. This is commonly done by measuring the current being drawn by the motor, which is how most dry-run detection devices on the market works. We measure the loading (current) of the motor during normal operation and we set a lower current value as the lower limit to trigger a warning or the immediate shut-off of the pump.