Danger
The danger of deadheading a centrifugal pump is that, as the liquid rotates, frictional forces cause its temperature to rise to the point where it vaporizes. The vapor disrupts cooling of the pump and may cause excessive wear and tear to its bearings. Deadheaded centrifugal pumps have been known to explode even if they contain just water or brine.
Protection
A centrifugal pump can be protected from the effects of deadheading by fitting a line, upstream of the outlet valve, to recycle liquid back to the inlet valve. The diameter of the line should be sufficient to recycle enough liquid to prevent the pump overheating.
Ammeter
The ammeter – the device that measures current flow – on a centrifugal pump is not a reliable indicator of deadheading. Centrifugal pumps typically use lower power and it can be difficult to distinguish between normal and abnormal operating conditions just by looking at the ammeter.