Pumps are essential in various industries, from water supply systems to chemical processing and oil refining. One crucial way to classify pumps is based on the number of impellers they use. Impellers are the rotating components that transfer energy to the fluid, determining the pump’s efficiency and application.
In this article, we will explore the classification of pumps based on impellers, their working principles, key components, and the advantages of each type.
Classification of Pumps Based on Number of Impellers
Pumps can be broadly divided into single-stage and multi-stage pumps, depending on the number of impellers used in their design.
1.1 Single-Stage Pump
A single-stage centrifugal pump is the simplest type of centrifugal pump, featuring one impeller mounted on a rotating shaft within the pump casing.
Working Principle: The impeller rotates, creating centrifugal force that pushes fluid outward. The kinetic energy is converted into pressure energy, allowing the fluid to move through the discharge pipe.
Applications:
- Suitable for high-flow, low-pressure systems
- Used in water circulation, HVAC systems, and irrigation
- Common in booster applications for water supply
Advantages:
- Simple design – easy to maintain and operate
- Cost-effective – fewer components result in lower production costs
- Higher efficiency – optimal for applications requiring high flow rates
Limitations:
- Not ideal for high-pressure applications
- Limited to moderate head requirements
1.2 Multi-Stage Pump
A multi-stage centrifugal pump consists of two or more impellers mounted on the same shaft. The impellers are arranged in series, progressively increasing the pressure of the fluid as it moves through each stage.
Key Components:
A multi-stage pump is constructed with four main sections:
Stator Section
Includes the suction section, discharge section, and guide vanes, which direct fluid from one impeller to another.
Rotor Section
Comprises the shaft, multiple impellers, balance disc, and shaft sleeve that support and regulate rotation.
Bearing Assembly
Consists of bearings, bearing body, and bearing glands that provide stability to the shaft during operation.
Shaft Seal System
Includes sealing box, packing material, and water-retaining ring to prevent leakage and maintain efficiency.
Applications:
- Ideal for low-flow, high-pressure applications
- Used in boiler feedwater systems, high-rise building water supply, and industrial pressure boosting
- Essential in reverse osmosis, power plants, and oil refineries
Advantages:
- Handles high-pressure applications without increasing motor size
- Energy-efficient – allows smaller motors to achieve high heads
- Reliable for long-distance fluid transport
Limitations:
- More complex maintenance due to multiple impellers
- Higher initial cost than single-stage pumps
Single-Stage vs. Multi-Stage Pumps: Key Differences
- The single-stage pump has high flow and low pressure whereas the multistage pump has low flow and high pressure.
- Single-stage has only one impeller whereas multistage has more than two impellers.
- Single-stage can’t be used for high head applications but multistage can be used for high head applications.
- Maintenance of multistage pumps is difficult than a single stage.
Choosing Between Single-Stage and Multi-Stage Pumps
- If your primary requirement is high flow at low pressure, a single-stage pump is ideal.
- If you need to pump fluid at high pressure over long distances, a multi-stage pump is the better choice.
- Industries like power generation, desalination, and oil refining require multi-stage pumps due to their ability to handle high-pressure requirements efficiently.