Axial Flow vs. Mixed Flow Pumps: Key Differences

Table of Contents

• Introduction: Selecting the Right Pump
• What is an Axial Flow Pump?
  • Submersible and Vertical Axial Pumps
  • Flow Characteristics of Axial Flow Pumps
  • Axial Flow Pump Uses and Applications
• What is a Mixed Flow Pump?
  • Flow Characteristics of Mixed Flow Pumps
  • Mixed Flow Pump Uses and Applications
• Key Differences: Axial vs Mixed Flow
  • Flow Direction & Discharge
  • Head and Flow Rate Comparison
  • Impeller Design and Structure
  • Efficiency and Performance
• Performance Comparison: Mixed vs. Axial
• Design Comparison: Mixed vs. Axial
• Choosing the Right Pump: Axial or Mixed?
• Conclusion & Contact

Introduction: Selecting the Right Pump

Choosing the correct pump can be daunting for engineers and planners. You need a pump that delivers the right combination of flow rate and pressure head for your application. In general, axial flow pumps excel at moving very large volumes of water with minimal pressure rise (ideal for irrigation, drainage or flood control), whereas mixed flow pumps handle heavy flow against higher head (ideal for municipal water supply, cooling circuits, etc.). Deciding which is best can be confusing. Sintech Pumps (India) supplies both axial and mixed-flow pump models to meet diverse needs: their SAF/SVAF horizontal and vertical axial pumps can handle up to 40,000 m³/hr, and their SMF/SVMF mixed-flow pumps achieve similar high flows at much higher head. This blog explains the key differences between axial and mixed-flow pumps so you can make an informed choice for your project. 

What is an Axial Flow Pump?

An axial flow pump pushes fluid parallel to the pump shaft, much like a boat propeller. It operates like a centrifugal pump, which is why it is sometimes called an axial-flow centrifugal pump. It has an axial flow impeller – curved blades that accelerate fluid straight along the axis. Because the impeller pushes water back along the shaft, axial pumps generate very high flow but very low head. For example, a large axial pump might move tens of thousands of m³/hr of water at only a few meters of head. They are most efficient under those low-head conditions.Sintech Pumps manufactures horizontal and vertical axial flow pumps (SAF, SVAF series) that can handle up to 40,000 m³/hr. These pumps use a simple propeller-like impeller. Compared to other pump types, axial pumps have a simple structure with few directional flow changes, which makes them easier to build and maintain. Because the impeller pushes fluid straight, there are minimal internal losses, contributing to good efficiency at their design point. At the same time, axial pumps can stall or lose efficiency if you try to push them against higher head than they are rated for. 

Submersible and Vertical Axial Pumps

Axial flow pumps come in different configurations. Vertical axial pumps are mounted with a vertical shaft and the impeller submerged below the water surface. In this setup, the impeller is always below water (in a sump or canal), giving a positive suction head. This self-priming design minimizes the footprint and eliminates the need for priming equipment. Sintech’s vertical axial pumps leverage this advantage: the impeller is immersed at startup, so they self-prime and are immediately ready to run. This built-in positive suction also prevents cavitation and improves reliability.In contrast, horizontal axial pumps sit above the water line and must be primed before operation. Sintech notes that suction-line losses (in foot valves, piping friction, etc.) in horizontal setups often prevent the pump from reaching its rated performance. The submerged vertical design avoids those losses and typically maintains higher efficiency and simpler installation.Submersible axial flow pumps are a specialized form where the entire pump–motor assembly is immersed in water. They have the same propeller-style impeller. These submerged axial pumps are ideal for moving huge volumes at low to moderate head. For example, they are often used in irrigation canals and flood control, because they can be placed right in the water source and pump water directly without any suction piping. 

Flow Characteristics of Axial Flow Pumps

The defining feature of an axial pump is axial flow through the impeller. Fluid enters and exits along the shaft line, producing a “straight-through” flow path. Consequently, axial pumps are high-flow, low-head machines. They efficiently transfer very large volumes (often thousands of m³/hr) but develop only small pressure (head) gains (typically only a few meters). If you force an axial pump to a higher head than it’s designed for, its flow will quickly drop off.Because the flow is streamlined and axial, the fluid velocity in an axial pump is very high. This makes them superb for bulk water movement. The flow through the impeller tends to be steady and laminar, which minimizes internal losses. Thus an axial pump often has high peak efficiency for the low-head range it’s meant for. However, this efficiency falls off rapidly as head increases. Beyond a few meters of lift, an axial pump may operate with very low efficiency or stall. 

Axial Flow Pump Uses and Applications

Axial flow pumps are chosen for applications demanding extremely high flow rates at low head. Common uses include:

• Agricultural Irrigation: Moving river or reservoir water to fields via canals. Axial pumps can transport water over long distances with minimal lift.
• Drainage and Flood Control: Dewatering construction sites, tunnels, or pumping out flooded basements and waterways. Their huge flow clears water quickly.
• Large-Scale Water Transfer: Conveying large volumes through canals or pipelines where the elevation change is small.
• Pumped-Storage Hydropower: Moving water between reservoirs in pumped-storage plants when large flow is needed.
• Wastewater Handling: Pumping sewage or effluent in low-lift sections of treatment plants (e.g. from wet wells).
• Aquaculture Ponds: Maintaining circulation in large fish or shrimp ponds.

In short, axial flow pump uses include any scenario where very large volumes of relatively clean water must be moved with only a small elevation gain. If your system requires a much higher head, an axial pump will not suffice. 

What is a Mixed Flow Pump?

A mixed flow pump combines aspects of both axial and radial pumps. It has a mixed-flow (diagonal) impeller that sends fluid partly forward and partly outward. In practice, water enters the impeller and is discharged at an angle relative to the shaft. The pump casing then collects this angled flow (often via a volute or diffuser) and directs it to the outlet. The result is a pump that delivers high flow like an axial pump but higher head like a radial pump.Mixed-flow pumps occupy the intermediate range between pure radial and pure axial designs. As KSB notes, a mixed-flow pump “covers the transition range between radial flow pumps and axial flow pumps”. In other words, it is essentially a type of centrifugal pump (often called a mixed-flow centrifugal pump) whose impeller imparts both radial and axial momentum. A typical mixed-flow impeller (also called a diagonal or helical impeller) has curved blades that impart some radial velocity to the fluid. As the impeller spins, it adds both backward and outward forces, producing a balanced flow/pressure combination.Sintech Pumps offers both vertical mixed flow pumps (SVMF series) and horizontal mixed flow pumps (SMF series). These pumps are built for large flow rates with moderate heads. For example, Sintech’s SVMF pumps can handle flows up to 44,000 m³/hr and lift water to around 20–30 m (even up to 300 m in special multi-stage units). In practice, a vertical mixed-flow pump like the SVMF can be installed submerged in a sump – effectively acting as a mixed flow submersible pump. 

Flow Characteristics of Mixed Flow Pumps

Mixed-flow pumps are designed for medium head and medium flow. Inside such a pump, the fluid gains velocity both radially and axially. The performance is a compromise: a mixed-flow pump moves large volumes of water (thousands of m³/hr) like an axial pump, but against significantly higher pressure (tens of meters of head) like a radial pump.

• Head (Lift): Mixed flow pumps can achieve heads on the order of 10–50 meters (per stage). They easily exceed the low few meters that axial pumps do. This makes them suitable for lifting water to elevated tanks or across moderate rises.
• Flow Rate: Flow rates are usually somewhat lower than a similarly-sized axial pump but still high (thousands of m³/hr). Typically, the flow-capacity lies between that of a comparable radial pump and an axial pump.
• Efficiency: Mixed-flow pumps generally maintain high efficiency in their operating range. Because their design smooths the flow path (with vanes and diffusers), they convert kinetic energy to pressure effectively. In fact, Liancheng notes mixed pumps “generally have high efficiency” in moderate head applications.
• Stability: The pump curve of a mixed-flow unit is usually flatter (more stable) than an axial pump. A mixed-flow pump will hold its flow more consistently as head changes, whereas an axial pump’s flow drops sharply with increasing head.

Construction-wise, mixed-flow pumps often use a volute or diffuser to guide the angled discharge, and many have semi-open impellers. The casing may include guide vanes. Sintech’s SMF mixed-flow pumps, for example, have semi-open, hydraulically balanced impellers to handle abrasive liquids. (This makes them better at solids handling than fully open impellers.) Mixed-flow pumps can be single-stage for moderate head or multistage if higher head is needed. 

Mixed Flow Pump Uses and Applications

Mixed flow pumps are chosen for applications requiring high flow with moderate head. Typical uses include:

• Industrial Cooling: Circulating cooling water in power plants or chemical plants where some pressure is needed to overcome system resistance.
• Process Industries: In paper mills, refineries or factories, mixed-flow pumps move process water or fluids through medium-head duties.
• Agriculture: Irrigation systems on sloped land or where a pump must lift water partway (e.g. from a river up to a higher canal).
• Drainage and Sewage: Lifting wastewater to treatment plants or pumping large stormwater volumes when modest lift is needed. Many sewage stations use mixed-flow (vertical turbine) pumps to elevate effluent.
• Marine/Offshore: Handling ballast, cooling or firewater on ships/platforms, where pump compactness and moderate head are required.
• Stormwater Control: Pumping runoff to sewers or retention basins when lifting against gravity.

In essence, mixed-flow pumps are the “middle ground” – they are the go-to when an axial pump’s head isn’t enough but a high-head radial pump would be overkill. 

Key Differences: Axial vs Mixed Flow

Flow Direction & Discharge

• Axial Pumps: Discharge fluid straight along the shaft axis. Fluid enters and exits in line with the shaft, so the pump outlet is usually in line with the inlet.
• Mixed Flow Pumps: Discharge fluid at an angle because the impeller throws fluid both backward and outward. The flow path is conical. As a result, the pump outlet is typically offset or requires a scroll casing/volute to collect the angled flow.

This means that piping layouts differ: an axial pump often uses straight or inline pipe runs, whereas a mixed-flow pump usually has an angled discharge port or volute. In vertical installations, an axial pump can pipe straight up or horizontally, while a vertical mixed pump pumps upwards at an angle.

Head and Flow Rate Comparison

• Axial Pumps: Designed for extremely high flow at low head. They will provide huge volumetric capacity (e.g. 10,000–40,000 m³/hr) but only generate a few meters of head. If your system requires even a moderate lift (say 10–15 m), an axial pump will stall or its flow will collapse.
• Mixed Flow Pumps: Engineered for large flow at medium head. Mixed pumps can develop tens of meters of head while still moving large volumes. For example, Sintech’s SMF/SVMF pumps might deliver ~15,000 m³/hr at 20 m head, whereas an axial pump of similar power might deliver 25,000 m³/hr at only 3–5 m head. As a rule of thumb: if required head is <5–10 m with very high Q, choose axial. If the head is larger (10–50 m) with still-high Q, choose mixed. Axial pump curves are very steep – flow falls off quickly with head, whereas mixed-flow curves are flatter and more forgiving.

For instance, an axial pump might pump 20,000 m³/hr at 5 m head but drop to near zero by 15–20 m. The comparable mixed-flow pump might deliver 15,000 m³/hr at 20 m. Thus, mixed-flow pumps cover duty points beyond axial range.

Impeller Design and Structure

• Axial Impeller: Looks like a large propeller or fan. It has wide, flat blades oriented along the shaft. Often only a few blades are used, and the impeller is open (no shroud). It pushes water straight back. Many axial impellers are unshrouded, although some have simple shrouds or side rings.
• Mixed Impeller: Has many curved, angled blades. The blades are twisted so they throw fluid both sideways and backward (diagonally). Mixed impellers often have partial shrouds or rings to handle the angled flow. Their shape is sometimes called helical or diagonal.

In the image above, the axial impeller (left) has flat fan blades, while the mixed-flow impeller (right) has steeper curved blades. This highlights the design difference: axial blades push fluid straight back, whereas mixed-flow blades direct it outwards at an angle.Structurally, mixed-flow pumps also have more robust casings (volutes or diffusers) to guide the angled discharge, and often include guide vanes or diffusers to recover pressure. Axial pumps usually have simpler straight-through housings. For example, Sintech’s horizontal mixed-flow pumps (SMF series) use semi-open, hydraulically balanced impellers, whereas axial pumps use open propellers.

Efficiency and Performance

• Axial Pumps: Very efficient at their design condition (high flow, low head). Because the flow is streamlined, they convert input energy to flow with low losses in that regime. However, they operate efficiently over a narrow head range. If forced to deliver a higher head, efficiency crashes.
• Mixed-Flow Pumps: Maintain good efficiency over a broader range of flow/head. Mixed pumps typically incorporate flow-smoothing features (shrouds, diffusers) that keep efficiency high in their medium-head range. In practice, a mixed-flow pump running at a moderate head may consume less power than an axial pump doing a similar job at a slightly higher head.

In summary, axial pumps “win” on pure volume (lowest head), and mixed pumps “win” on combination of volume + head. KSB notes that mixed pumps operate with medium head and flow on a relatively flat curve, whereas axial pumps deliver very large flow at low lift on a steep curve. Therefore, axial pumps save energy when only flow matters, but mixed-flow pumps use energy more effectively if some head is required.

Performance Comparison: Mixed vs. Axial

In practice, the choice boils down to your duty point (flow Q and head H):

• Axial-Pump Performance: Excellent volume but minimal head. For example, an axial pump may achieve 10,000 m³/hr at 5 m head, but its flow quickly falls off beyond 5–10 m. It has a very steep pump curve.
• Mixed-Pump Performance: High volume with moderate head. A mixed-flow pump might deliver 8,000–15,000 m³/hr at 15–25 m head and only taper off near 40–50 m. Its curve is flatter.

In simple terms: Axial pumps are more efficient for low-head, high-volume tasks; Mixed-flow pumps are better when some head (tens of meters) is needed. For example, Sintech’s data might show an axial pump outputting 25,000 m³/hr at 3 m, whereas a similar mixed-flow pump might output 15,000 m³/hr at 20 m.Looking for the right solution for your project? Reach out to Sintech Pumps today to get expert guidance on selecting between axial and mixed flow pumps for maximum efficiency and reliability.

Design Comparison: Mixed vs. Axial

Looking at actual pump designs reveals their differences:

• Axial Pump: Often built with a large-diameter, open or semi-open impeller. Many vertical axial units (e.g. Sintech’s SVAF series) have a submerged column and a simple propeller impeller. The casing is straightforward and there are few internal parts.
• Mixed Pump: Has a more compact, multi-bladed impeller with blades angled diagonally. Its casing typically includes a volute or diffuser. Sintech’s SMF pumps, for instance, use semi-open, hydraulically balanced impellers for abrasion resistance. Mixed pumps can be single-stage or multi-stage to achieve higher head.

Maintenance-wise, axial pumps have simpler internals (few parts) but their open propellers can jam on debris. Mixed-flow pumps have more components (diffuser vanes, multiple stages) but often include wear rings or bushings and can tolerate some solids in the fluid.

Choosing the Right Pump: Axial or Mixed?

To select between them, follow these steps:

1. Define your duty: Determine the required flow (Q) and head (H) at your operating point.
2. Check the curves: If your duty point lies at very low head (e.g. <5–10 m) with high flow, an axial pump is usually ideal. If the head needed is higher (e.g. 10–50 m) with still-large flow, a mixed-flow pump is typically better.
3. Consider installation: Axial pumps usually need straight piping and may be vertical, while mixed pumps might need suction guidance.
4. Account for fluid: Mixed pumps (especially semi-open types) are better if fluid has some solids.
5. Efficiency and cost: Compare expected power draw and cost. Axial pumps often cost less per unit flow but mixed pumps save energy if you need higher head.

Example: If you need 12,000 m³/hr at 5 m head, an axial pump is the efficient choice. If you need 12,000 m³/hr at 20 m head, a mixed-flow pump will perform much better. If the head exceeds ~50–60 m, consider a radial or multistage pump instead. Whenever in doubt, consult pump curves or Sintech’s engineers. 

Conclusion

Understanding whether to use an axial flow pump or a mixed flow pump comes down to matching your flow and head needs. Axial pumps (e.g. Sintech’s SAF/SVAF models) move enormous volumes at low head, while mixed-flow pumps (SMF/SVMF series) move large volumes at higher head. By comparing flow direction, performance curves and impeller designs, you can select the pump that fits your application.Choosing the right pump at the design stage saves time, energy and money in the long run. If you have questions about your specific needs, Sintech’s experts can provide guidance on pump selection and sizing. Feel free to contact Sintech Pumps for a consultation or quote. With the right pump, you’ll achieve efficient, reliable water handling for years to come

FAQs

1. What is the difference between axial and mixed flow pumps?

An axial flow pump moves water parallel to the shaft using an axial flow impeller, giving very high flow at low head. A mixed flow pump, using a mixed flow impeller, discharges fluid diagonally, balancing flow and pressure. In short, axial and mixed flow pumps differ in flow direction, head capacity, and applications—axial suits flood control, while mixed flow centrifugal pumps serve water supply and industrial cooling.

2. What is the main difference between an axial flow propeller pump and a mixed flow propeller pump?

An axial flow centrifugal pump with a propeller impeller pushes fluid straight along the shaft, delivering high-volume, low-head performance. In contrast, a mixed flow centrifugal pump directs fluid at an angle, combining radial and axial motion to handle moderate head with high flow. While a vertical axial pump is ideal for irrigation, a vertical mixed flow pump or mixed flow submersible pump works for municipal and industrial duties.

3. What are the advantages of mixed flow pumps?

A mixed flow pump offers versatility by bridging the gap between radial and axial types. With its mixed flow impeller, it achieves higher head than an axial flow pump while still maintaining large flow rates. Advantages include balanced efficiency, suitability for municipal water supply, industrial cooling, and drainage. A vertical mixed flow pump or mixed flow submersible pump is compact, reliable, and ideal for medium-head, high-flow operations.

4. What are the advantages of axial flow pumps?

An axial flow pump delivers massive volumes of water at very low head, making it highly efficient for dewatering, flood control, and irrigation. Its axial flow impeller minimizes energy loss, while submersible axial flow pumps and vertical axial pumps offer compact, self-priming designs. Common axial flow pump uses include agriculture, cooling water circulation, and wastewater handling, where continuous high flow at minimal lift is critical for reliability and performance.