Centrifugal Pump Impeller Types

You have no doubt observed that centrifugal pumps are used is a wide variety of applications. While the pump family uses centrifugal force to pump water, there are different ways to apply that force. One of the key differences in the various centrifugal pump designs it the type of impellers that are used. Impellers have vanes that flow from the center to the outer edge of a circle. As the impeller rotates, it pulls liquid in at the center, or eye, of the impeller, and the spinning vanes create the centrifugal force that pushes the liquid to the outside of the pump casing, and ultimately out the discharge port.

There are three basic impeller designs

• Closed Impellers
• Semi-open Impellers 
• Open Impellers

 The names of these types of impellers give you a sense of their design.

Closed Impellers have vanes that are  “sandwiched” between two solid, circular plates. The liquid travels through the channels between the impellers and between the plates. This design creates the most efficient flow from the eye to the discharge port. While this is the most common type of impeller, centrifugal pumps with this design are intended for clear liquids.

 Semi-open impellers have vanes that are attached to a single plate, leaving the other side of the impeller exposed to the interior of the pump housing. This design is less efficient than the closed impeller because the liquid is immediately interacting with the rest of the liquid in the pump casing. However, this design is also more forgiving of suspended particles in the liquid and can handle more viscous fluids. 

The Open impeller design centrifugal pump is, as the name suggests, has vanes open on both sides. Because vanes do not have support on either side, they tend to be weaker. Though they can handle suspended solids, these pumps are smaller and less powerful in order to reduce the frequency of braking vanes. Additionally, due to the open design, the liquid flowing into the pump interacts with the liquid already in the casing, causing this type of centrifugal pump to be the least efficient. 

The type of impeller used in a centrifugal pump will depend on the intended use of the pump.

Most often, applications call for the most efficient flow of liquid possible, which is a job for the closed impellers. These are the strongest design, allowing them to move higher volumes of water faster. However, users must be certain that the liquids are clear and use filters on the intake hoses to prevent oversized solids from entering the pump.

When you are looking for a new pump, and decide a centrifugal pump is your best option, be sure you’ve considered the various conditions in which you will be using the pump. Too often people make the purchase with the best case scenario in mind (clear H2O), and then end up using the pump for liquids other than water, or water with lots of suspended solids.

It is possible that your needs vary to such a degree that you will either need two pumps or must accept less efficient pumps in the ideal conditions in order to have a pump that can handle the outlying situations.

Don’t cut corners on your pump. Downtime and repairs may cause more headaches than you imagine.