Top OEMs for Propeller and Axial Flow Pumps in Water & Wastewater Applications

1. Introduction

In the hydraulic landscape of municipal and industrial water management, propeller and axial flow pumps occupy a specific, critical niche: the movement of large volumes of water at relatively low heads. Unlike radial flow centrifugal pumps that rely on centrifugal force to generate pressure, axial flow pumps utilize the lifting action of propeller blades to push fluid parallel to the pump shaft. This design characteristic dictates their primary application in flood control, stormwater management, raw water intake, and wastewater treatment plant (WWTP) recirculation loops.

For the consulting engineer and plant operator, specifying these pumps requires a distinct mindset compared to standard end-suction or split-case pumps. The specific speed ($N_s$) of axial flow pumps is typically high (usually above 9,000), necessitating rigorous attention to intake design, submergence levels, and discharge piping geometry to prevent vortex formation and cavitation. Furthermore, because these units often serve as the primary defense against catastrophic flooding or are critical to the biological process of a treatment plant (e.g., nitrate recycle), reliability is not merely an operational preference but a regulatory and safety mandate.

The market for these pumps is dominated by Original Equipment Manufacturers (OEMs) that have invested heavily in hydraulic modeling, metallurgy, and large-scale manufacturing capabilities. Selecting the right OEM is complex. It involves evaluating not just the catalog performance curve, but the manufacturer’s ability to provide computational fluid dynamics (CFD) support for intake structure design, their history of support for legacy installations, and the robustness of their mechanical sealing and bearing systems under heavy load.

This article provides a technical, specification-grade analysis of the leading OEMs in the propeller and axial flow category. It eschews marketing narratives to focus on engineering deliverables, lifecycle costs, and application suitability, ensuring that decision-makers can navigate the procurement process with technical clarity.

2. How to Select This Pump Type

Selection of propeller and axial flow pumps goes beyond matching a duty point to a curve. The physics of high-flow, low-head applications introduce variables that can lead to catastrophic mechanical failure if not addressed during the specification phase. The following criteria outline the essential technical considerations.

Hydraulic Performance and Curve Characteristics

Axial flow pumps possess a distinct performance curve profile. The head-capacity curve is typically steep. More critically, the power curve is opposite to that of a radial flow pump: brake horsepower (BHP) is highest at shut-off (zero flow) and decreases as flow increases. This presents a unique risk profile:

• Start-up Conditions: Engineers must specify soft starters or variable frequency drives (VFDs) carefully. Starting against a closed valve—common practice for radial pumps—can cause motor overload and shaft breakage in axial units due to peak horsepower requirements at zero flow.
• Siphon Breakers: In discharge over-the-levee applications, siphon breaker valves are mandatory to prevent backflow and to reduce static head requirements during start-up.
• Operating Range: These pumps have a narrower preferred operating region (POR) than radial pumps. Operation far to the left or right of the Best Efficiency Point (BEP) induces severe vibration and recirculation cavitation.

Solids Handling vs. Hydraulic Efficiency

A fundamental trade-off exists between efficiency and solids handling. The classic propeller design mimics a ship’s propeller, offering exceptional efficiency but poor handling of stringy solids (rags, wipes).

• Stormwater vs. Wastewater: For clean stormwater or raw water, standard hydrofoil blade profiles are acceptable. However, for WWTP recirculation (mixed liquor) or combined sewer applications, “swept-back” or self-cleaning propeller geometries are required to shed fibrous materials.
• Specification Note: Engineers must define the maximum sphere size, but more importantly, the nature of the solids. If the application involves raw sewage, a propeller pump may require an upstream screening system, or the specification must explicitly call for “non-clogging” hydraulic geometry, limiting the OEM pool to those with specific wastewater-grade propellers.

Materials of Construction

Given that these pumps are often submerged for years, material selection dictates the lifecycle.

• Propellers: Aluminum bronze or Nickel-Aluminum Bronze (NiAlBr) is standard for strength and cavitation resistance. For wastewater or brackish water, Duplex Stainless Steel (e.g., CD4MCu or ASTM A890) is preferred to resist pitting and stress corrosion cracking.
• Bowls and Columns: Cast iron is standard, but fabricated steel columns are common in large storm stations. The interface between dissimilar metals (e.g., a stainless propeller in a carbon steel housing) requires sacrificial anodes to prevent galvanic corrosion.
• Coatings: In abrasive environments, ceramic-epoxy coatings on the wear ring or bowl liner can extend life, though they add cost and complexity to repairs.

Installation Environment and Intake Design

The most common cause of failure in axial flow pumps is not the pump itself, but the intake structure. High velocities require uniform flow distribution.

• ANSI/HI 9.8 Standards: Specifications must mandate compliance with Hydraulic Institute standards for intake design. Poor intake geometry leads to floor and surface vortices, causing noise, vibration, and uneven loading on the impeller.
• Submergence: Adequate submergence is critical to prevent air entrainment. Engineers must calculate submergence based on the lowest operating level, not the average.
• Column vs. Submersible:
  • Vertical Line Shaft: Motor is above grade (dry). Easier motor access, but requires long drive shafts and intermediate bearings which are maintenance-intensive.
  • Submersible (in tube): Motor and pump are a single submerged unit seated in a discharge tube. Eliminates long shafts but requires hoisting the entire unit for service. This is increasingly the industry standard for ease of installation.

Maintenance and Serviceability

The sheer size of these units (often 24 to 60+ inches in diameter) complicates maintenance.

• Cable Entry (Submersibles): The cable entry point is a frequent failure mode. Look for designs that isolate the cable terminal chamber from the stator housing to prevent water ingress from traveling down a damaged cable into the motor windings.
• Wear Rings: Axial pumps rely on tight clearances between the propeller tips and the bowl/liner. Replaceable wear liners are a mandatory specification requirement to restore efficiency without replacing the entire discharge bowl.
• Blade Adjustment: Some OEMs offer adjustable pitch blades. This can be done statically (bolt adjustment when pulled) or dynamically (while running, similar to a Kaplan turbine). While dynamic adjustment offers incredible efficiency across varying flows, it introduces significant mechanical complexity and seal maintenance.

3. Comparison Table: Top OEMs

The following comparison analyzes the five designated OEMs based on their typical market positioning, technological strengths in the axial/propeller category, and operational considerations.

OEM	Primary Configurations	Key Technological Strengths	Limitations / Considerations	Best-Fit Application
Fairbanks Nijhuis (Pentair)	Vertical Line Shaft, Submersible Axial, Horizontal Axial	Extensive custom hydraulic coverage for massive flows. Strong legacy in flood control and “fish-friendly” pump designs. Offers adjustable pitch blades for flow control.	Large, custom units often have long lead times. Line shaft designs require rigorous alignment maintenance.	Large-scale flood control stations, raw water intake, and applications requiring fish-safe certification.
Flygt (Xylem)	Submersible (PL Series) in Column	Standardized, modular “Slimline” propeller pumps. N-Technology (self-cleaning) adapted for axial flow. superior cable sealing (Active Seal) and monitoring integration.	Primarily focused on submersible column installations; less focus on line-shaft retrofits. Fixed catalog sizes may require civil work to match.	WWTP recirculation (anoxic zones), stormwater stations requiring compact footprints, and high-ragging environments.
KSB	Submersible (Amacan), Vertical Line Shaft (SEZ)	Amacan series features robust motor cooling jackets and direct-drive efficiency. Strong metallurgical options (Duplex/Super Duplex). ECB propellers for high efficiency.	German engineering standards can sometimes necessitate proprietary parts or specialized service tooling.	Industrial process water, large municipal stormwater, and aggressive wastewater environments requiring exotic metallurgy.
Sulzer	Submersible (VUPX), Vertical Axial	Strong focus on wastewater hydraulics with skewed blade geometry for solids handling. Premium efficiency motors (IE3/IE4 equivalent). Robust mechanical seal protection systems.	Similar to Flygt, heavily focused on the submersible market. Specification requires careful matching of propeller pitch to duty point.	Combined sewer overflow (CSO) pumping, activated sludge recirculation, and lift stations with variable head conditions.
Smith & Loveless	Engineered Vertical, Process Systems	Specializes in complete packaged systems and custom-engineered retrofits. High durability in specific process loop applications. Focus on ease of operator access (top-side).	Less prominent in the “mega-pump” flood control market (100″+ sizes) compared to Fairbanks/KSB. Niche focus on process over general bulk water transfer.	Specialized WWTP process loops, packaged treatment plants, and retrofits requiring custom vertical engineering.

4. Top OEM Manufacturers

The following detailed analysis covers the specific product lines and engineering philosophies of the mandated OEMs. This evaluation is based on technical merit, construction quality, and installed base performance.

Fairbanks Nijhuis (Pentair)

Fairbanks Nijhuis represents the union of two historic heavyweights in the pump industry. In the realm of propeller and axial flow pumps, they are frequently the standard for massive scale infrastructure projects.

Technical Focus: Their portfolio is dominated by both vertical line shaft and submersible configurations. The distinguishing feature of Fairbanks Nijhuis is their ability to manufacture enormous units (up to 150 inches or more in diameter) for flood control. From an engineering standpoint, their “Fish-Friendly” pumps are a critical differentiator. These pumps utilize a unique impeller geometry and wide flow passages to minimize shear stress and impact, allowing safe passage for aquatic life—a growing requirement in river intake specifications.

Engineering Pros: They offer adjustable pitch blades, allowing operators to alter the blade angle to meet changing head/flow conditions. This is particularly valuable in flood control where static head varies significantly with river levels. Their rugged construction often utilizes heavy cast components designed for 40+ year lifecycles.

Engineering Cons: The complexity of adjustable pitch mechanisms requires specialized maintenance. For line shaft pumps, the alignment of intermediate bearings over long column lengths is critical and installation-sensitive.

Flygt (Xylem)

Flygt, a brand of Xylem, fundamentally shifted the axial flow market by popularizing the submersible propeller pump seated in a discharge column (the PL series). Their philosophy centers on modularity, ease of installation, and integrated intelligence.

Technical Focus: The Flygt PL 7000 series is the industry benchmark for submersible column pumps. Their engineering strength lies in the integration of the motor and hydraulics. The units are compact (“Slimline”), minimizing the required column size and reducing civil construction costs. Flygt has also adapted their “N-Technology” (self-cleaning hydraulics) concepts to their axial flow lines, employing backswept leading edges on propellers to shed rags and fibrous materials common in wastewater recirculation.

Engineering Pros: The “Active Seal” system in their submersibles pumps oil from the reservoir into the seal gap, preventing liquid ingress. Their monitoring integrated units (MAS 711) provide deep data on vibration, temperature, and leakage, enabling predictive maintenance. The Formed Suction Intake (FSI) device is an available accessory that conditions flow entering the pump, allowing for smaller wet wells by mitigating vortex formation.

Engineering Cons: Being a standardized product line, customization of the casting dimensions is limited compared to line-shaft manufacturers. Retrofitting a Flygt PL into a non-standard legacy tube often requires adapter rings or tube modifications.

KSB

KSB is a German engineering giant known for extreme precision and robustness. Their Amacan series (submersible motor pumps in discharge tubes) and SEZ series (vertical tubular casing pumps) are staples in the global water market.

Technical Focus: KSB focuses heavily on hydraulic efficiency and motor thermal management. The Amacan P series utilizes a slim motor design that minimizes flow blockage in the discharge tube. KSB’s proprietary ECB (Energy Saving) propellers are designed using advanced CFD to minimize turbulence and maximize wire-to-water efficiency. They are also leaders in material science, frequently supplying Duplex stainless steel variants for desalination intake or aggressive industrial wastewater where standard cast iron would fail.

Engineering Pros: KSB motors often feature redundant sealing systems and robust bearing arrangements capable of handling the high axial thrust loads inherent in propeller pumps. Their “cable entry” design is exceptionally robust, utilizing resin potting to prevent capillary action of water into the motor—a common failure point in competitors.

Engineering Cons: Spare parts availability can sometimes be tied to European supply chains depending on the specific model size. Their technical documentation and selection software are highly detailed but require a knowledgeable engineer to navigate effectively.

Sulzer

Sulzer operates in the same heavy-duty submersible space as Flygt and KSB, with the VUPX series being their flagship axial flow offering. Sulzer’s heritage includes the ABS product lines, bringing significant wastewater expertise to their axial designs.

Technical Focus: Sulzer differentiates itself through a focus on “real-world” wastewater conditions. Their propellers are designed with specific skew angles to handle higher solids concentrations without stapling (rag accumulation). The VUPX series is designed for installation in standard steel or concrete tubes and features a unique coupling system that ensures automatic connection to the discharge piping via the pump’s own weight, ensuring a leak-free seal.

Engineering Pros: Sulzer places a high emphasis on premium efficiency motors (IE3/IE4 equivalent). Their mechanical seal protection system is designed to prevent winding or clogging around the seal face, which is vital in recirculation applications involving mixed liquor suspended solids (MLSS). They offer excellent support for retrofitting existing stations, often providing custom-sized wear rings or adapters.

Engineering Cons: Like other submersibles, the unit must be pulled for any motor or hydraulic service. Engineers should pay close attention to the specific lifting requirements, as the weight distribution of the VUPX series requires verified lifting davits.

Smith & Loveless

Smith & Loveless (S&L) occupies a unique position in this list. While not a volume manufacturer of generic flood control pumps like KSB or Fairbanks, they are a premier OEM for engineered systems and specific treatment process applications.

Technical Focus: S&L is renowned for wet-well mounted pumps and vacuum priming systems, but in the context of axial flow, they are typically involved in custom-engineered solutions for treatment plants or specific loop reactor applications. Their approach is often “above-grade” maintenance. They design systems where the mechanical components are accessible without entering the wet well, although this applies more to their centrifugal lines. For axial applications, they focus on process reliability and package integration.

Engineering Pros: S&L equipment is famous for longevity; systems installed 40 years ago are often still in operation. Their engineering team is highly adept at solving unique hydraulic constraints in retrofits where standard off-the-shelf pumps will not fit. They focus heavily on the complete system—controls, piping, and pump—rather than just the rotating assembly.

Engineering Cons: Their product range for pure axial flow (high flow/low head) is more niche compared to the broad catalogs of the other four. They are often a specific solution provider rather than a general commodity pump supplier for this category.

5. Application Fit Guidance

Matching the OEM to the application is critical for project success. While all five manufacturers can technically supply a pump for most applications, their “sweet spots” vary.

Municipal Wastewater (Recirculation & Lift)

Preferred OEMs: Flygt, Sulzer.
In activated sludge processes, nitrate recycle, and headworks lifting, solids handling is the primary constraint. Flygt and Sulzer have the most developed “wastewater-specific” propeller geometries (backswept blades) designed to shed rags. Their submersible designs allow for easy installation in the tight concrete channels common in WWTPs.

Stormwater and Flood Control

Preferred OEMs: Fairbanks Nijhuis, KSB.
When flow rates exceed 50,000 GPM and reliability is a matter of public safety, the massive vertical line shaft or large-scale submersible units from Fairbanks and KSB are dominant. Fairbanks is particularly strong where adjustable pitch is needed to manage varying river levels. KSB is excellent for deep tunnel stormwater applications requiring high-voltage submersible motors.

Raw Water Intake and Irrigation

Preferred OEMs: Fairbanks Nijhuis, KSB.
For clean water abstraction from rivers or lakes, efficiency is the driving factor. The hydraulic profiles of Fairbanks and KSB are optimized for these steady-state conditions. If “Fish-Friendly” pumping is a regulatory requirement, Fairbanks Nijhuis is often the default specification.

Industrial and Process Loops

Preferred OEMs: Sulzer, Smith & Loveless, KSB.
For industrial applications requiring specific chemical resistance or custom footprints, these OEMs excel. KSB’s metallurgy options make them a fit for saline or aggressive chemical loops. Smith & Loveless is ideal when the pump is part of a larger, integrated treatment package.

6. Engineer & Operator Considerations

Beyond the catalog selection, several practical engineering factors influence the long-term success of an axial flow pump installation.

Maintenance Access and Safety

The Weight Factor: A 48-inch submersible axial flow pump can weigh several tons.
Engineering Action: During the design phase, confirm that the lifting davit or crane has the capacity and the reach to center over the discharge tube. Many operators struggle with davits that were under-designed, forcing the rental of mobile cranes for routine seal inspections.

Line Shaft vs. Submersible:
Operator Feedback: Operators often prefer line shaft pumps because the motor is dry and accessible. However, changing the bottom bearing on a 30-foot column requires pulling the entire pump. Submersibles require pulling the unit for any service, but the mechanism for pulling (guide rails/cables) is usually faster than unbolting column flanges.

Vibration and Structural Resonance

Axial flow pumps generate significant low-frequency energy.
Design Risk: “Reed frequency” resonance occurs when the natural frequency of the pump column matches the running speed (or vane pass frequency) of the pump. This leads to catastrophic structural failure.
Specification Requirement: Always require a modal analysis (resonance test) from the OEM for the installed configuration, especially for variable speed applications.

Common Specification Mistakes

• Oversizing: Specifying too much safety margin on head. Axial pumps operating at low head (high flow) relative to their design point suffer from rough running and cavitation. They must be selected tightly to the system curve.
• Ignoring Cable Management: For submersibles, the power cables are heavy and susceptible to damage from turbulence. Specify stainless steel cable support grips and a dedicated cable management system (Kellems grips or similar) to prevent cable fatigue at the entry gland.
• Neglecting Start-up Torque: Propeller pumps have high inertia. Ensure the electrical system can handle the long ramp-up times, and that the shaft (if line shaft) is rated for the starting torque, particularly if the pump might be started with debris settled around the propeller.

7. Conclusion

The selection of a propeller or axial flow pump is a high-stakes engineering decision. These machines move the lifeblood of water infrastructure—flood waters, raw sewage, and cooling water—often under duress.

Among the top OEMs, Fairbanks Nijhuis stands out for massive scale and flood control versatility; Flygt (Xylem) leads in standardized, wastewater-resilient submersible technology; KSB offers precision engineering for high-efficiency and industrial durability; Sulzer provides a robust alternative for wastewater reliability; and Smith & Loveless serves the market for specialized, engineered process solutions.

For the consulting engineer and the end-user, the goal is to align the pump’s hydraulic and mechanical characteristics with the specific constraints of the site. A “clean water” propeller in a raw sewage application will fail, regardless of the brand prestige. Conversely, a heavy-duty wastewater pump in a clean water irrigation loop may incur unnecessary power costs. By focusing on intake design, solids loading, and realistic maintenance capabilities, engineers can specify a system that delivers decades of reliable service.

source https://www.waterandwastewater.com/top-oems-for-propeller-and-axial-flow-pumps-in-water-wastewater-applications/