Are Positive Displacement Pumps Self-Priming?

In principle, all positive displacement pumpsVibrator Motors Manufacturers in China are self-priming. In particular, this includes rotary gear pumps (internal and external), lobe pumps, vane pumps and diaphragm pumps. A common feature of all positive displacement pumps is the use of close-tolerance parts to prevent fluid returning from the discharge to the suction side. Depending on the effectiveness of these seals created by these close-tolerance parts, a positive displacement pump is capable of venting air from its suction line to some extent. However, under dry running conditions, a pump may overheat and this can cause seal wear and pump failure.

With reciprocating pumps, there is also a danger of cavitation occurring at the point when liquid starts to enter the pump and there is a liquid/air mixture. Under these conditions, vapour bubbles form and expand on the suction side of the pump. Upon reaching the high pressure, discharge side of the pump, the bubbles collapse violently causing vibration and damage to the pumping elements.

For these reasons, it is important to refer to the manufacturer before using a positive displacement pump in an application where it must self-prime and, of necessity, be run dry for any period.