Pump impellers are essential components of all pump types used in water. They are the rotating substances that transfer energy to the fluid and create pressure that allows it to move.

These impellers are made from iron, steel, and bronze and come in various sizes and designs, each affecting how well the pump performs.  A well-designed impeller ensures smooth flow and reduces turbulence, making the pump work more efficiently.

The impeller’s backward-curved vanes help boost the pump’s efficiency, whereas the impeller’s diameter determines the head or pressure the pump generates.

Understanding the different types of impellers and how they work can help you choose the right type of pump for your specific needs.

Working Of Impellers

Impellers are placed in the middle of any pumping system to ensure efficiency. They transfer energy into pump fluid by continuously rotating and creating a centrifugal force using wear rings.

It first pulls the water in through a central opening called the “eye.” Then, as the impeller starts spinning, it creates a centrifugal force.

This force moves the fluid outwards into the pump’s discharge from the centre of the impeller. Fluid velocity and pressure are created as the fluid moves through the impeller’s vanes.

Numerous types of impellers are used in domestic and industrial pumps. Let’s discuss those types.

Types of Impellers

1. Open Impeller

In an open impeller, the vanes are attached to the central hub without a cover. These impellers are used in inexpensive pumps to pump low-viscosity fluid with suspended solids.

The open design reduces the risk of clogging compared to other types, making them ideal for such applications. Due to recirculation between the impeller inlet and discharge, these pumps use low flow pressure.

Open impellers are primarily used in treating wastewater, mining, chemical and food industries as the popular choice.

Advantages

• Open impellers don’t block easily as they don’t have a small clearance.
• They are easy to manufacture and install, and they cost less.
• These can operate at a higher speed than other impeller types.
• These impellers are easy to clean and repair since most parts are visible.

 Disadvantages 

• These are less efficient than other impeller types as the flow isn’t guided between impeller vanes.
• The gap between the impeller, suction and casing can cause leaks from the discharge section.
• Open impellers are structurally weaker.
• They require a higher NPSH to prevent cavitation.

2. Semi-open Impeller

Semi-open impellers are the type of impeller in which vanes are attached to one side of the central hub and the other is open. They are suitable for medium-diameter pumps with a small amount of soft solids.

These impellers strike a balance between open and closed impellers in terms of NPSH and efficiency. Semi-open impellers are used in most average centrifugal pump sizes in the chemical, mining, and food industries.

Advantages

• Due to NPSH efficiency, semi-open impellers are a good compromise between an open impeller and a closed impeller.
• It can handle a moderate amount of suspended liquid without getting blocked.

Disadvantages

• These are more difficult to manufacture and maintain than open impellers. 
• Semi-open impellers are not as good at handling solids as open impellers. 
• These impellers are less effective in some applications. The large gap between the impellers and pump casing leads to leaks.

3. Closed Impeller

A closed impeller is used with high efficiency and requires low NPSH. The vanes are covered with a cover or shroud and closed from both sides. This type of impeller is best suited for low-viscosity liquids with low-suspended bodies.

It is used in large pumps to transfer clean liquids in water treatment, mining, and paper and pulp industries. These pumps rely on close-clearance wear rings to reduce axial loads and help maintain efficiency.

Advantages 

• Closed impellers are more efficient and durable than other type of impellers.
• Walls of closed impeller increase its strength and reduce the shaft load.

Disadvantages

• These are prone to clogging when in contact with solids.
• They have a complicated design and are expensive compared to others.
• Closed impellers are difficult to clean & maintain.

4. Vortex Impeller 

A vortex impeller is quite similar to the shape of a semi-open impeller and is designed for handling liquids with solid particles.

The pump creates a whirlpool or vacuum that keeps solids away without allowing particles to come into direct contact with the impeller, reducing the risk of clogs or damage.

The vortex impeller has a hollow chamber to handle fluid with high gas content. It is mainly used in the oil and gas industry and has a huge space between itself and the casing volute. 

Advantages 

• They are best for pumping liquid with gas or air in it.
• They have a low risk of blocking and clogging.
• Vortex impellers can handle fluids with dirty solids by creating a whirlpool that keeps solids away from the impeller.

Disadvantages 

• Vortex impellers are less efficient than other types of pumps.
• These impeller types can suffer from air lockage.

5. Chopper impeller

Chopper impellers are also called cutter impellers as they have sharp-edge cutter vanes. 

These vanes are used to grind any solid before entering the pump. By cutting up the solids, chopper impellers ensure a smoother flow and reduce the risk of blockages or damage to the pump system.

This impeller type is best in sewage treatment and other waste treatment where the channel impeller will clog.

Advantages 

• Solids are reduced in size as they are being pumped.
• It can handle large or tough solids like sewage, sludge, manure, and similar thick liquids.

Disadvantages 

• Chopper impellers have lower efficiency than other types of impellers.
• When the pump accumulates for hours of operation, its ability to reduce solids is diminished.

6. Screw Impeller

The screw impeller design is aligned to the channels that allow for solids to be openly handled when rotating. It is a suitable application for pumps as it has a lower shear ratio and can handle thick fluid with large solids. 

Advantages

• Screw impellers are self-prime and are easy to install.
• These have solid structures and can handle a huge range of liquids.

Disadvantages

• Screw impellers are quite expensive than other pump impeller types
• Due to its anatomy, these are only used for end-section pumps.

Factors To Consider While Choosing An Impeller

Flow Rate And Head

The flow rate refers to the fluid the pump can deliver at a given time. It is expressed as gallons per minute (GPM).

The head is the maximum height at which the pump can lift the fluid. It is expressed in feet or meters. When selecting an impeller for your use, you should check the flow rate and use it.

Fluid Type

Different impellers are available for different fluid types, so you can make a decision based on your requirements.

Some impellers are ideal for handling liquids with gas substances as they provide low pressure, while others are best for solid particles, so check the fluid type before you select the pump.

Material

Considering impeller materials can resist corrosion, it can be from stainless steel, cast iron or bronze.

Stainless steel is the most common impeller material because it has anti-corrosive, anit-heat and anti-containment properties. Bronze material is good for liquid with salt, whereas cast iron is not suitable for acidic liquid.

Viscosity

It affects pump efficiency and refers to fluid resistance to flow. A fluid with high viscosity requires more pressure than a liquid with low viscosity.

Diameter of Impeller

The diameter of the impeller also impacts the pump performance, so it is essential to know its size. The impeller can handle more fluid with a larger diameter, resulting in a high flow rate and energy consumption.

The smaller impeller diameter consumes less energy and handles low fluid, leading to a lower flow rate.

Pricing

The price of impeller types is also an important factor to consider. You need an impeller that meets your needs and fits your budget.

Read More: Top 10 Submersible Pump Companies In India

Conclusion

Selecting the right impeller type is important as it is responsible for the pump’s performance. Each impeller is designed for different tasks, whether it’s handling clean water or dealing with solids.

The impeller affects how much fluid a pump can move and the pressure generated. The suitable impeller helps run the pump smoothly, saves energy, and reduces maintenance.

Knowing the function and various impeller types will help you choose the right pump that aligns with your application’s requirements and ensure reliable, efficient pump operation.

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