Centrifugal Pumps – How Do They Work?

Pumps are vital equipment in many industries, including mining, construction, manufacturing, chemistry and pharmaceuticals. The most widely used pump is a centrifugal pump. They come in many sizes and shapes and can be used for clean water and wastewater but also toxic and corrosive chemicals/fluids depending on the materials used in construction.

The principle behind centrifugal pumps

No matter the application or liquid pumped, all centrifugal pumps work along the same basic principle. They all involve an impeller, which is a rotor that rotates the fluid via the action of centrifugal force to create a low pressure zone at the center. This causes the fluid to enter the impeller due to atmospheric differences. The fluid which enters the impeller is then changed in direction by the impeller and this fluid then exits the impeller at the outer diameter. The fluid then enters either the volute or diffuser (depending on which style of pump is being used), which results in the fluid increasing in force until the design discharge head is achieved.

A volute pump has a spiral casing enclosing the impeller which is offset to the impeller whereas a diffuser pump has a circular casing with secondary internal vanes enclosing the impeller which is central to the impeller.

The different parts of a centrifugal pump

The impeller is a rotor with so-called curved vanes that help rotate the fluid. The impeller always has to be submerged in fluid, including when the pump is first started so as not to cause pump damage due to dry running.  Some pumps are self-priming however still need this initial fluid fill to submerge the impeller.

The volute, from the outside of the pump, simply looks like the casing, however it fulfils a special function. A volute is a spiral-like form that captures the liquid that is discharged from the impeller. The volute areas increase at a rate proportional to the discharge of liquid from the impeller and maintains a constant velocity around the periphery of the impeller.

The vaned diffuser is surrounded by gradually-expanding passages formed by stationary guide vanes. In this type of casing, the velocity head of the liquid leaving the impeller is converted more completely into pressure than in the volute type, potentially making its efficiency slightly higher. However, the added cost and more complicated construction of the vaned diffuser pump, compared with a single volute, are generally not considered justifiable for the efficiency advantage alone, except in high-pressure pumps.

What are centrifugal pumps used for?

As stated, centrifugal pumps are the most commonly used type of pump in the world. They have a wide array of applications and can be useful in many industries. One way in which centrifugal pumps play an important role in all of our lives is their use in sewage systems, which keep our water safe and our daily lives hygienic.

Malcolm Thompson Pumps supplies and services a wide range of centrifugal pumps – learn more by clicking here.

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