Priming of Centrifugal Pumps

Pumping systems designed with suction lift features need “priming” before they will operate. Pumping systems that are designed with a suction head (also referred to as “flooded suction”) do not need priming. Before we discuss priming let’s discuss how a centrifugal pump works.

The impeller of a centrifugal pump rotates and imparts centrifugal energy to the water present in the pump housing. As a result, the energized water flows to the circumferential areas of the pump from where it finds its way to the discharge piping.

As water is expelled to the circumferential regions of the pump, vacuum is created at the center (impeller’s eye) of the pump. Atmospheric force pushes water on the suction side into the impeller. Thus water flow through the pump continues.

The important thing to note here is that a centrifugal pump will start operation only if it can create vacuum within its body. And to create vacuum, it must have water present in it. In some situations, when a pump is stopped, most of the water drains out of it into the suction piping. Therefore, it is left without adequate water in its body to start up.

This is where priming comes in. The term “priming” refers to the procedure required to fill the body of a centrifugal pump so that it can be started. Once the body of a pump is filled with water, it can be started. As the pump starts up, it will create its own vacuum and draw water in from the suction side.

In this section we will discuss some common methods used for priming of centrifugal pumps.