Centrifugal vs Axial Flow Pumps: Key Differences

Choosing the right pump depends on your needs. Centrifugal pumps are best for higher pressure and medium flow, while axial flow pumps excel at moving large volumes of water at low pressure. Here’s a quick summary:

• Centrifugal Pumps: Ideal for medium-flow, high-head applications like municipal water systems, mining, and industrial processes. They handle pressures up to 2,000+ metres and flow rates up to 10,000 m³/h.
• Axial Flow Pumps: Perfect for high-flow, low-head tasks like flood irrigation, stormwater management, and flood control. They can move up to 500,000 m³/h at heads up to 15 metres.

Quick Comparison

Feature	Axial Flow Pump	Centrifugal Pump
Flow Rate	5,000–500,000 m³/h	Up to 10,000 m³/h
Pressure (Head)	1–15 metres	10–2,000+ metres
Best Use Case	High-flow, low-head tasks	Medium-flow, high-head tasks
Efficiency	Better at low heads	Better at medium to high heads
Applications	Flood irrigation, dewatering	Urban water supply, mining

Key takeaway: For high-pressure, medium-flow needs, go with a centrifugal pump. For high-volume, low-pressure tasks, an axial flow pump is the better choice.

Design and How They Work

To truly appreciate the strengths and applications of centrifugal and axial flow pumps, it’s essential to understand how they operate. Each pump type moves fluids differently, which directly influences its performance and suitability for specific tasks. Let’s break down how these technologies function and explore their design differences.

How Centrifugal Pumps Work

Centrifugal pumps rely on the principle of centrifugal force to move liquids. At the heart of the pump is a rotating impeller that creates suction and propels fluid through a system of pipes ^[3].

When the impeller spins within its housing, it pushes the fluid outward from the centre, creating a radial flow. This movement increases pressure through a combination of radial force and changes in velocity ^[6]. The centrifugal action essentially “throws” the fluid tangentially off the blade tips, which is why the impeller is often compared to a “thrower” ^[5]. Once the fluid gains speed from the impeller, it enters the volute or diffuser, where it slows down. This deceleration converts the fluid’s kinetic energy into pressure energy ^[9].

“When one considers the theory of operation of a centrifugal CF pump, its rotating element acts as a spinning disk with blades that can be viewed as a ‘thrower,’ meaning that the fluid is captured and thrown tangentially out off the blade tips. In contrast, axial CF pump rotating elements operate like a propeller in a pipe and can be viewed as a ‘pusher.'” – Nader Moazami, MD et al. ^[5]

This mechanism makes centrifugal pumps ideal for medium to high-head applications, where lifting fluid to greater heights or maintaining higher pressure is necessary ^[9].

How Axial Flow Pumps Work

Axial flow pumps take a different approach, using a propeller-style impeller to move fluid along the shaft axis. This creates a streamlined, straight-line flow pattern ^[6]. Unlike centrifugal pumps, these pumps act more like a “pusher”, similar to how a propeller moves water in a pipe ^[5].

The axial flow impeller directs fluid along the shaft’s axis, which means these pumps don’t rely on centrifugal action ^[3]. Instead, they operate based on lift theory, drawing from aerodynamic principles to generate thrust ^[6].

“The axial flow impeller discharges fluid along the shaft axis. For this reason an axial flow pump is by definition not ‘centrifugal’ in its pumping action.” – PIA Australian Pump Technical Handbook (2007, p.30) ^[3]

This design makes axial flow pumps highly efficient for moving large volumes of liquid at low pressure. They minimise energy loss and friction, making them perfect for applications requiring rapid transport of substantial quantities of fluid without significant lift ^[4]. The straight-line flow parallel to the shaft allows for high flow rates with minimal discharge pressure ^[8]. These characteristics set axial flow pumps apart and make them indispensable in certain scenarios.

Key Design Differences

The most noticeable differences between these pumps lie in their impeller design and the direction of fluid flow. Centrifugal pumps typically feature a volute casing, which helps convert velocity into pressure. In contrast, axial flow pumps have a simpler structure, resembling a straight water pipe ^[6].

Flow direction is another key distinction. Centrifugal pumps create a radial flow pattern that moves liquid outward, while axial flow pumps maintain a straight-line flow parallel to the shaft ^[6].

Performance also varies significantly. Centrifugal pumps, with specific speeds below 300, are best suited for high-lift, low-flow tasks. On the other hand, axial flow pumps, with specific speeds above 500, excel in moving large volumes of liquid at low lift ^[6].

Power requirements behave differently as well. Axial flow pumps demand more power as flow decreases, which is the opposite of centrifugal pump behaviour ^[7]. This difference plays a critical role in energy management and operational planning.

These design distinctions are key when selecting the right pump for South Africa’s diverse water management needs, whether it’s irrigating farmlands in the Free State or supporting municipal water treatment systems in urban areas.

Performance and Efficiency Comparison

When comparing pumps, performance metrics such as flow rate, pressure generation, and energy efficiency are key factors that highlight their differences. These distinctions play a critical role in selecting the right pump for specific operational needs. Each pump type is designed to meet particular demands, making it essential to understand their unique capabilities.

Flow Rate Capabilities

The most noticeable difference between axial flow and centrifugal pumps lies in their flow rate capacities. Centrifugal pumps handle flow rates ranging from 50 to 1 200 ℓ/s, making them ideal for medium-volume uses. On the other hand, axial flow pumps are designed to manage much larger volumes, typically 1 500 to 4 000 ℓ/s, making them the go-to choice for high-volume applications^[2].

These flow rate variations significantly influence system design. For example, axial flow pumps can achieve flow rates between 5 000 and 500 000 m³/h, making them indispensable for systems requiring rapid water movement, such as flood control or large-scale irrigation. In contrast, centrifugal pumps generally handle flow rates up to 10 000 m³/h, which is better suited for medium-scale operations. Understanding these differences helps align pump selection with specific project requirements.

Pressure Generation

Another critical factor is the ability to generate pressure. Centrifugal pumps shine in medium to high-pressure applications, delivering heads ranging from 10 to over 2 000 metres, making them suitable for tasks requiring substantial lift. Conversely, axial flow pumps are designed for low-pressure scenarios, producing heads between 1 and 15 metres^[2].

Feature	Axial Flow Pump	Centrifugal Pump
Pressure Generation	Low to moderate (1–15 m)	Medium to high (10–2 000+ m)
Best Application	High-flow, low-head	Medium-flow, high-head

Centrifugal pumps tend to show greater variations in flow as pressure changes, while axial flow pumps adjust by increasing pressure when system resistance rises^[5]. These pressure characteristics directly affect their energy consumption patterns, making it essential to match the pump type with the operational requirements.

Energy Efficiency

Energy efficiency varies depending on the operating conditions of each pump type. Axial flow pumps are more efficient at lower heads, whereas centrifugal pumps excel at medium to high heads. For instance, at operating speeds of 1 500 rpm or higher, centrifugal pumps can outperform axial pumps by 5% or more. The best efficiency point for centrifugal pumps can reach up to 85%, compared to less than 80% for axial flow pumps in similar conditions. However, axial flow pumps can achieve volumetric efficiencies exceeding 90% at lower speeds^[10].

This efficiency gap has practical implications in South Africa, especially in areas with limited power resources. For example, Rand Water, which supplies approximately 4,7 billion litres of drinking water daily, relies on centrifugal pumps for their high-head efficiency, helping to manage operational costs effectively^[11]. Ultimately, axial flow pumps are better suited for high-flow, low-lift tasks, while centrifugal pumps are the preferred option for medium-flow, medium-head applications^[1].

Industry Applications

South Africa’s diverse industries rely on specific pump types to meet their unique operational needs. Here’s how these pumps play a role in addressing challenges across key sectors.

Agriculture and Irrigation

In agriculture, choosing the right pump is essential to ensure efficient water delivery. Axial flow pumps excel in flood irrigation systems, moving large volumes of water at lifts below 4 m – perfect for covering wide areas quickly. On the other hand, centrifugal pumps are the go-to choice for pressurised systems like centre pivot and drip irrigation. These pumps generate the higher pressures needed for precise and controlled water distribution, ensuring crops get the right amount of water exactly where it’s needed.

Water Treatment and Municipal Systems

Municipal water systems often depend on centrifugal pumps for their ability to deliver consistent, high-pressure flow, even under elevated temperatures^[14]. These pumps are integral to water treatment plants, handling tasks like chemical dosing, filtration, and ensuring stable water distribution networks.

For applications requiring the movement of large water volumes at lower pressures, axial flow pumps are highly effective. They are commonly used in stormwater management and flood control projects. A notable example comes from the Eastern Cape in July 2022, where axial flow pumps were installed in a recirculated aquaculture system. These pumps moved 5,500 ℓ/min at a 4-m lift and featured enhanced corrosion protection to withstand challenging conditions^[15].

Industrial and Mining Uses

The industrial and mining sectors also benefit greatly from these pumps, each offering unique advantages tailored to specific tasks. Centrifugal pumps are robust and well-suited for handling viscous fluids, slurries, and abrasive materials, making them indispensable in mining operations. Their durability allows them to process liquids containing solids and harsh chemicals without significant wear^[8][12].

In contrast, axial flow pumps are ideal for dewatering large areas. For instance, opencast coal mines in Mpumalanga use these pumps to quickly remove floodwater and transfer large volumes of water efficiently, thanks to their high flow rate capabilities.

Application Type	Preferred Pump	Advantage
Slurry Handling	Centrifugal	Handles abrasive materials and solids effectively
Large Area Dewatering	Axial Flow	Excels at moving high volumes at low lift
Chemical Processing	Centrifugal	Provides precise flow control and pressure

Industrial facilities like petrochemical plants in Secunda and paper mills in KwaZulu-Natal also rely on centrifugal pumps for chemical processing, where precise flow and pressure control are crucial. Meanwhile, axial flow pumps are often used for tasks like cooling water circulation and other low-pressure, high-volume transfers.

Maintenance and Operating Costs

When it comes to owning pumps, the upfront cost is just the beginning. Maintenance, energy consumption, and reliability all play a big role in determining the total cost of ownership.

Maintenance Requirements

Centrifugal pumps require periodic maintenance – ranging from routine to quarterly and annual checks – focused on identifying critical failure points^[16]. One benefit of centrifugal pumps is their design, which allows easier access to impellers for inspections and replacements.

Axial flow pumps, on the other hand, involve tasks like bearing lubrication, seal inspections, vibration analysis, and discharge monitoring. Their design also makes it possible to remove the entire rotor for repairs, which can simplify certain maintenance tasks^[19].

Both types of pumps need regular checks on bearings, seals, and vibration levels. Routine inspections typically include monitoring oil levels and condition, listening for unusual noises, checking for leaks, and assessing the condition of the seal chamber^[19]. Following manufacturer recommendations – such as timely lubricant changes and monitoring bearing temperatures^[17] – is essential for keeping these systems in good working order. Additionally, regularly inspecting and replacing mechanical seals can help avoid unexpected downtime^[18].

Equipment Lifespan

The lifespan of a pump depends heavily on its operating conditions and how well it’s maintained. Axial flow pumps generally run between 8,000 and 12,000 hours before needing major repairs, while centrifugal pumps last a bit longer, averaging 10,000 to 15,000 hours.

However, most failures in centrifugal pumps are tied to bearings and mechanical seals. Statistics show that over 85% of bearing failures result from contamination – whether dirt, foreign material, or water^[20]. For example, just 250 parts per million (ppm) of water can reduce bearing life by a factor of four^[20].

Pump speed also plays a major role. A pump running at 3,550 rpm can wear out 4 to 8 times faster than one operating at 1,750 rpm^[20]. To maximise lifespan, it’s important to operate pumps near their best efficiency point (BEP) and keep suction-side fluid velocity below 10 feet per second – ideally under 8 feet per second^[20].

Factor	Impact on Lifespan	Recommended Action
Water contamination	Reduces bearing life by 4x at 250 ppm	Maintain proper sealing systems
Operating speed	Higher RPM reduces life 4–8x	Use speed ratings suited to the task
Temperature fluctuations	Limit to <1.1°C per minute	Manage temperature changes carefully

These factors directly affect how long a pump lasts, which in turn influences its overall cost-effectiveness.

Long-term Cost Analysis

The true cost of owning a pump goes well beyond the initial purchase price. Effective maintenance not only extends the pump’s lifespan but also cuts down on energy use and repair bills. Pumps account for over 20% of global electricity consumption^[22], and in some industries, they can use between 25% and 50% of a facility’s total energy^[22].

Energy efficiency varies depending on the type of pump and its application. Axial flow pumps are typically more efficient at lower heads, while centrifugal pumps perform better at medium to high heads^[1]. Choosing pumps that operate within their best efficiency range improves both performance and reliability^[22].

Studies highlight the financial benefits of a reliability-centred approach to maintenance. For instance, one study reduced annual labour costs from R5,890,000 to R4,500,000, while another achieved savings from R5,540,000 to R4,140,000^[21]. Additionally, implementing Piping Plan 13 API 682 on a centrifugal pump boosted productivity by 19.75% and slashed repair expenses by 76.12%^[21].

Using electronic variable speed drives (VSDs) can further lower long-term costs. VSDs help regulate pump speed, keeping it close to the best efficiency point, which reduces both energy consumption and mechanical wear^[22]. Selecting the right materials for pump components also helps prevent premature failures^[22].

In short, regular maintenance programmes that replace worn parts promptly can significantly extend the life of a pump system and reduce overall operating expenses^[16][22].

South African Operating Conditions

South Africa’s distinct climate, water quality, and infrastructure challenges play a crucial role in determining the suitability of centrifugal or axial flow pumps. By taking these factors into account, businesses and farmers can achieve better pump performance and durability, tailored to the diverse conditions across the country.

Regional Irrigation Requirements

South Africa’s agricultural landscape is incredibly varied, and so are its irrigation needs. Depending on the region, different pumping systems are required to handle variations in terrain and water availability. For example, pumps in South Africa can manage flow rates ranging from 30 litres per second at 100 metres of head to 2,000 litres per second at 25 metres of head ^[13].

In areas like the Lowveld, where flood irrigation is widely practised and surface water is abundant, axial flow pumps are often the smarter choice. These pumps are more energy-efficient for low-lift irrigation tasks, such as lifting water up to 2.8 metres ^[24]. On the other hand, the Highveld’s pressurised irrigation systems benefit from centrifugal pumps, which are ideal for medium to high head applications ^[23]. Beyond agriculture, centrifugal pumps are commonly used in urban water supply, fire protection systems, and various industrial processes ^[23]. This regional variation highlights how pump selection must align with specific local needs and conditions.

Power Supply Challenges

South Africa’s ongoing power supply issues, particularly load shedding, have a profound impact on pump operations. In 2023 alone, the country endured over 6,800 hours of load shedding ^[26], with economic losses estimated at around R1 billion per stage, per day ^[25]. Such frequent power outages make it essential to invest in reliable backup systems to maintain operations.

“The electricity system is still vulnerable, with the supply gap between available and needed power remaining tight.” – Cyril Ramaphosa, President of South Africa ^[26]

Water Quality and Climate Effects

The country’s water quality and climate also significantly influence pump maintenance and performance. Over the decade from 2011 to 2020, South Africa experienced more than 1,800 extreme weather events, with floods being the most common ^[27]. These conditions demand the use of corrosion-resistant materials to ensure pump durability, especially in regions like the Western Cape, where extreme weather occurs more frequently. Such areas also require more rigorous inspection and maintenance schedules ^[27].

Choosing the Right Pump Type

When deciding between centrifugal and axial flow pumps, your choice should hinge on factors like flow rate, pressure, and the specific requirements of your application. Here’s what you need to keep in mind:

Flow rate and pressure play a crucial role in selecting the right pump. If your system requires a high flow rate (ranging from 5,000 to 500,000 m³/h) but operates at a low head (1–15 metres), an axial flow pump is the way to go. On the other hand, for medium flow rates (up to 10,000 m³/h) with a high head (10–2,000+ metres), a centrifugal pump is better suited ^[2].

The viscosity of the liquid is another important consideration. Axial flow pumps are ideal for low-viscosity fluids, while centrifugal pumps are better equipped to handle thicker, more viscous liquids or those containing solids ^[1].

Space constraints can also influence your decision. Axial flow pumps, with their compact design, are perfect for installations in confined areas. In contrast, centrifugal pumps, which are often larger, are better suited for moving liquids across long distances, such as in urban water systems ^[1].

Don’t overlook long-term costs. The total cost of ownership includes not just the initial purchase price but also energy, maintenance, and repair expenses. Energy usage, in particular, forms a significant portion of a pump’s life cycle costs ^[29]. Axial flow pumps, while efficient within a narrow operating range, can experience increased energy consumption, vibration, noise, and wear if operated outside their optimal conditions ^[28]. These factors should be carefully weighed alongside performance and maintenance considerations to ensure a well-rounded decision.

For more specific guidance tailored to your flow rate, head, and fluid properties, it’s always a good idea to consult experienced pump suppliers ^[1]. Matching the pump to your operational needs will help maximise both efficiency and longevity.