Automatic, Positive Pumping
Whenever air or vapor is present at the start of the pumping operation – or when there is a loss of suction because of air or vapor during pumping – the priming pump automatically moves air and vapor from the suction line to the discharge line.

Once the flowing liquid from the centrifugal portion of the pump builds up sufficient pressure in the discharge system, this pressure backs up through a tube to act on the bottom of the priming pump’s moveable slide block, placing it in a neutral position. Under these conditions the priming pump no longer evacuates air, but merely circulates a small amount of liquid.

Roto-Prime Pumps are actually two pumps in one. The small, powerful vane-type pump within the main centrifugal housing can prime an absolutely dry 4" (100 mm) line with zero back pressure in approximately two seconds per foot without initial manual priming. And this priming pump will evacuate suction lines with back pressures up to 8 pounds per square inch.