Application Note

Protecting Pumps From Dead Head Conditions

Source: Eaton
Protecting pumps from Dead Head Conditions

The C445 motor management relay offers the most configurable protection options in the industry, with features specifically designed to protect critical pumps from costly damages due to dead-head and other underloaded or starved pump conditions.

What is a dead-headed pump?
A dead-head is when a centrifugal pump operates with no flow through the pump due to a closed discharge valve or line blockage. The pump re-circulates the same water, causing water temperature to continually rise. If a pump is run in a dead-headed condition for too long, excessive heating can damage expensive seals and reduce the life of the pump.

Why is a dead-head hard to detect?
A pump float switch will not detect a dead-head because the water level does not decrease. The key to accurate pump protection against dead-head damage is that the motor load decreases. Two methods are available to determine motor load: motor current and input power. However, monitoring current for underloaded conditions is not effective because current is nearly constant up to 50% of the motor load. Current is high even at light loading and the power factor is high, as current is flowing to the motor but it is not doing useful work (power).