The Unique Characteristics of Centrifugal Water Pumps
Centrifugal pumps come in several forms for a variety of applications. They vary in size, capacity, and ability and are distinctly different to positive displacement pumps. Usually, centrifugal pumps are used in agriculture, municipal (water and wastewater), power generation, petroleum and gas and many other industries.
So, how does it work?
Centrifugal water pumps are best for pumping water and other low viscosity fluids. The impeller, submerged in water, rotates within a casing. When running, the impeller spins quickly, and the centrifugal force from this rotation pushes the water out of the casing through a discharge port, and additional water enters through the suction port.
The velocity conveyed to the liquid by the impeller is then converted to pressure energy or head. This makes them great for moving high volumes of low viscosity fluids at very fast speed. However, none of the liquid can get into the motor or any other important areas, because the liquid from intake to out is separated. If you need to know more about the workings of a centrifugal pump, you can watch this quick and informative video.
Centrifugal pumps are unique due to the higher flowrates they can provide – when compared to positive displacement pumps. This flowrate can vary according to any changes in the total dynamic head (TDH) of the piping system. This allows you to throttle the flowrate as required by placing a simple valve in the discharge piping, without causing a buildup of pressure. This makes centrifugal water pumps suitable for many liquid pumping applications.
Let’s go into two unique characteristics of centrifugal water pumps in more detail:
1. Throttling Flowrates
As mentioned, one unique advantage of centrifugal pumps is the fact that you can throttle flowrates to slow the pump/motor speed on a centrifugal water pump using a discharge valve, which is relatively inexpensive compared to a variable frequency drive (VFD). However, you do need to beware of throttling below the minimum safe flowrate indicated by the manufacturer, or throttling excessively, which will cause the shaft to deflect, increasing wear on bearings and seals. The ideal flowrate is near its Efficiency Point (BEP) as this ensures optimal energy efficiency and increases seal and bearing life.
Centrifugal pumps are best suited for pumping liquids with low viscosity like water or a light oil. Centrifugal pumps become less efficient with even a slight rise in viscosity, which means pumping them requires more horsepower. Should your facility pump viscous liquids like fertilizers or chemicals, we usually recommend positive displacement pumps to minimize horsepower requirements and keep energy usage low. For more on viscosity, read: Why viscous fluids shouldn’t go near centrifugal pumps.
Some drawbacks to centrifugal water pumps
One of the biggest issues with centrifugal water pumps is that they don’t have suction power, which means they must be installed below the liquid or primed before they can work. They’re also not recommended for viscous liquids (especially if the pump has a magnetic drive) or for heavy loads that might cause the coupling to slip.
Centrifugal pumps are good for most applications, but not all. If you’re unsure what pump is the right choice for you, give us a call on 1-800-367-4180 (toll-free). We are your centrifugal pumps supplier in Canada and we’re here to help you choose, install, maintain, and monitor a variety of equipment. And to answer questions about things you’ve previously tried gone wrong.