How Self Priming Pumps Work

Hunker may earn compensation through affiliate links in this story.

When you have a messy, muddy water issue or a slick of viscous liquid, a self-priming pump is a life saver. The pumping system is built to work with oil, debris-filled water, sewage and other liquids that have found a way into the wrong place, as well as with other jobs that require large amounts of fluids to be redistributed. Knowing how the self-priming pump works can help you decide on the type of pump you hope to buy or how to troubleshoot a pump that seems to be stopping under pressure.

How Self Priming Pumps Work
Image Credit: Huntstock/DisabilityImages/GettyImages

How the Pump Works

A self-priming pump uses an air and water mixture in order to reach its fully primed state. While called a self-priming pump, it is actually a centrifugal jet pump working principle. It uses force to create a pumping action by using a pressure differential in a liquid. That sounds much more complicated than it is. The blades take the fluid in the pump and flick it against the walls of the casing. When the pump is in the priming cycle, air is introduced to the water at the impeller. Mixed together in the water reservoir by the impeller, the air will eventually rise, leaving the water to sink in the casing. Once all the air is removed, the water continues to mix with the air that is coming through the suction line. Once a vacuum is created in the suction line, the water is forced up into the suction line due to atmospheric pressure and is moved toward the impeller. This keeps the pump humming along.

The next time the pump roars to life, it is already self-primed and is able to work on its own. Water must always be present in the casing in order for the pumping system to work.

Different Uses of Self-Priming Pumps

The self-priming pump can be used with many different types of fluids that have built up or need to be removed or moved. For instance, it can be used to pump sewage from basements or kitchens, as well as for oil or gray water that backs up into a home or office. It can also come with two impellers rather than one, depending on what the pump is used for. The impellers and casing can be made from plastic, metal or composite materials, all of which carry their own benefits.

Monoblock Pump Working Animation

Sturdy and reliable, a centrifugal monoblock pump can be beneficial for agriculture, civil projects and industrial projects that require clean water or fluids to be moved. A monoblock pump working animation can show exactly how the wheel of the impeller moves the water and air through the casing, separates the two and self-primes when restarted. When the motor and pump are built together and housed in the same casing, they don't need a coupling device between the separate shafts since they are coupled directly, hence the monoblock moniker. They are the preferred pumps for clean fluids that aren't chemically enhanced so as not to damage the pump components.


Kimberley McGee is an award-winning journalist with 20+ years of experience writing for a variety of clients, including The New York Times, Las Vegas Review-Journal Home section and other national publications. As a professional writer she has researched, interviewed sources and written about home improvement, interior design and related business trends. She earned a B.A. in Journalism from the University of Nevada, Las Vegas. Her full bio and clips can be viewed at

View Work