Exploring Impeller Types: Open, Semi-Open, Closed, Vortex, Cutter or Screw

Centrifugal pumps are vital in numerous industries, ranging from water management and oil refining to pharmaceutical production and power generation. The impeller lies at the heart of these powerful machines, a critical component that transfers the motor’s power to the fluid. The pump’s impeller has rotating vanes that come off an open inlet known as the eye; these rotating vanes create a centrifugal force as they turn that moves the liquid from the casing to the discharge points (find out more about how an impeller works here). In this article, we will delve into the main impeller types used for centrifugal pumps.

1. Open Impeller

Open impellers are designed with vanes completely open on both sides, offering maximum passage for the fluid. These impellers are preferred for pumps that handle highly contaminated or viscous fluids and those containing solids. Open impellers are more susceptible to wear and damage, but they provide easier access for maintenance and cleaning. They don’t have support on each side, so they tend to be used in smaller, inexpensive pumps that don’t operate under significant strain. They are often used in mining, dredging, slurry pumping, and other industries dealing with challenging fluid conditions but require a higher NPSH to operate without cavitation and loss of efficiency.

2. Semi-Open Impeller

Semi-open impellers feature vanes that are open on one side, allowing the fluid to enter the impeller passages. Their back wall shroud adds mechanical strength to the vanes while remaining open on the other side. These impellers are commonly used for applications involving fluids with higher viscosity or small amounts of solids. The open side of the vanes facilitates the passage of such particles, reducing the risk of blockages. However, the clearance between the vanes and pump casing must be small, as slippage or recirculation can otherwise occur. Semi-open impellers find applications in wastewater treatment, chemical processing, and pulp and paper industries.

3. Closed Impeller

The closed impeller consists of a solid disk with curved vanes that are closed on both sides, providing maximum strength. Closed impellers are particularly suitable for handling clean fluids with minimal solids or abrasive particles, as they are prone to clogging. They have a more complicated, expensive design because they rely on close-clearance wear rings to reduce axial load and maintain efficiency. They are ideal for applications in water supply, HVAC systems, and general-purpose pumping.

4. Vortex Impeller

A vortex impeller is similar in appearance to the semi-open, but they have more space in the volute. The design of the vortex impeller creates a vacuum or vortex as the liquid is pulled through, keeping solids away from the impeller and preventing damage to internal components. With minimal risk of clogging and excellent solids handling, a vortex impeller is typically used in sewage or other applications that contain trash, debris, or solids. However, they offer lower efficiencies, so vortex impellers are not usually the first choice of impeller for centrifugal pumps.

5. Cutter Impeller

Cutter impellers are designed to handle solids. The design incorporates sharp-edged, scissor-like vanes to grind or shred any solids before they enter the pump. These cutters slice like scissors through solids to prevent clogging and minimize issues downstream. Where the efficiency of cutter impellers is low, they are the ideal impeller for pumping sewage and other waste where a channel impeller will clog. However, the ability of a cutter impeller to handle solids depends on the sharpness of the cutter vanes, which means their ability to shred will decrease over time.

6. Screw Impeller

The screw impeller is a highly efficient and clog-resistant solution designed explicitly for pumping thick fluids and large solids. Its unique screw-like, open-channel design allows these solids to pass through the pump while minimizing shear, making it ideal for handling sensitive fluids. As a result, the screw impeller achieves exceptional efficiencies in fluid movement and is resistant to clogging, ensuring reliable operation even in challenging conditions.

Final thoughts

Impellers are the lifeblood of centrifugal pumps, enabling the efficient movement of fluids across various industries. Understanding the different types of impellers and their respective applications is essential for pump engineers and professionals in choosing the right impeller design for specific fluid handling needs.

Whether the closed impeller for clean fluids or the open impeller for challenging fluid conditions, we’re here to help you find the right impeller type and centrifugal pump. Contact us at 1-800-367-4180 (toll-free) to discuss your options. As Canada’s leading centrifugal pump supplier, we can help you choose, install, maintain, and monitor any pump and impeller. And answer questions about things you’ve previously tried gone wrong.