How Does a Centrifugal Pump Work? A Beginner’s Guide

Centrifugal pumps are among the most widely used pump types in industrial applications due to their simplicity and efficiency. They rely on centrifugal force to move fluids through a system, making them ideal for transferring liquids in a variety of industries, including manufacturing, water treatment, and food processing. 

But how does a centrifugal pump work, and what are its key components? This guide will break it down step by step.

Centrifugal pumps are often chosen for their ability to handle:

• High flow rates with consistent pressure.
• Continuous operation with minimal maintenance.
• Customizability to fit specific needs, including material choices like stainless steel, cast iron, or bronze for compatibility with different fluids.
• Varying flow rates and pressure conditions.

Centrifugal Pumps are often the most cost effective pump for an application, with both low upfront costs and little to no maintenance required when compared to other types of pumps, especially all positive displacement pumps. 

Key Components of a Centrifugal Pump

Before understanding how a centrifugal pump works, it’s important to familiarize yourself with the main pump components:

Impeller: A rotating component with vanes or blades that accelerates the fluid outward.

Impellers come in three main types: open, semi-open, and enclosed. Open impellers are simple and ideal for fluids containing solids but are less efficient. Enclosed impellers, by contrast, are more efficient and suited for clean liquids. The choice of impeller depends on the specific application requirements.

Casing: A stationary housing that directs the fluid into the pump and collects it after it leaves the impeller. 

Casings can be designed as concentric casings, with a volute or with diffusers, and their geometry is critical for pump efficiency. Special coatings or materials, such as stainless steel, may be used for the casing to resist corrosion or abrasion in demanding environments.

Concentric casings are used in low flow (less than 200 gpm) or high pressure (higher than 75 psig) pumps.  Volutes are most common in larger pumps where flows are high relative to the pressure.  Diffusers are used most often in high head pumps where more than one impeller is needed for very high pressures.

Suction and Discharge Ports: The suction (inlet) port allows fluid to enter, while the discharge (outlet) port directs it out of the pump.

The orientation and size of these ports are determined by the pumps flow rates and the need to connect to the piping systems. Standardized flange connections help ensure the pump integrates seamlessly into existing setups.

Pump Shaft: Connects the impeller to the motor or drive mechanism.

In larger pumps, the shaft’s alignment is crucial to prevent vibration and wear. High-precision bearings are used to support the shaft and ensure smooth operation.

Mechanical Seal or Packing: Prevents leakage around the rotating shaft.

Mechanical seals are preferred in modern pumps because they minimize leakage and reduce maintenance requirements compared to traditional packing systems. Specialized seals, such as double or cartridge seals, are available for handling hazardous or abrasive fluids.  Packing is rarely used in pumps today.

How Does a Centrifugal Pump Work?

The operation of a centrifugal pump can be summarized in three main steps:

1. Fluid Entry (Suction)

Fluid enters the pump through the suction port, a critical stage influenced by pressure dynamics. To draw the fluid into the pump, a low-pressure zone is created at the eye (center) of the impeller. This low-pressure area is typically generated by the impeller’s rapid rotation, which reduces static pressure at the impeller’s eye relative to the atmospheric or system pressure at the suction port.

The pressure differential forces the fluid into the pump. For this to occur efficiently, it is essential to maintain a continuous flow without cavitation, which happens when the suction pressure falls below the fluid’s vapor pressure. Proper suction line design, including adequate pipe diameter and minimal bends, is key to optimizing fluid entry and preventing disruptions.

Be sure to check the pumps required net positive suction head (NPSHr) is satisfied by the available suction pressure (NPSHa).  If there is not enough suction pressure at startup the pump will cavitate, make a lot of noise and eventually destroy the impeller.

2. Acceleration (Impeller Rotation)

Once the fluid enters the pump, it reaches the rotating impeller, which is the primary energy-transferring component. The impeller blades accelerate the fluid radially outward through centrifugal force. This outward movement imparts significant kinetic energy to the fluid, increasing its velocity.

The impeller’s design – including blade curvature, diameter, and rotational speed – directly affects the pump’s performance. For example, the vane angles of the impeller blades will determine whether the pump has relatively high efficiencies and relatively low NPSHr. The impeller’s material must also match the application to resist wear, corrosion, or temperature extremes.

3. Conversion of Energy (Casing)

As the high-velocity fluid exits the impeller, it enters the volute or diffuser within the pump casing. Here, the casing plays a pivotal role in converting the fluid’s kinetic energy into pressure energy (also known as head).

• Volute Design: A spiral-shaped casing gradually increases in cross-sectional area, slowing the fluid velocity while raising its pressure.
• Diffuser Design: A series of stationary vanes surrounding the impeller reduces velocity more systematically, ensuring efficient energy conversion with minimal turbulence.

The result is a pressurized fluid stream that exits the pump through the discharge port. The discharge pressure depends on factors like impeller speed, casing design, and the fluid’s density. This high-pressure fluid is then ready to be transported through the system.

Contact American Stainless Pumps Today

At American Stainless Pumps, we deliver high-performance, close-coupled, customizable centrifugal pumps designed to meet the demands of your industry. So, whether you need a standard solution or a tailored design, our pumps will provide the durability and efficiency your operation requires.

Contact us today to discuss your needs and discover how our commercial stainless steel pumps can optimize your processes.