Top OEMs for Mixing Equipment

1. Introduction

Mixing equipment serves as the kinetic heart of municipal and industrial water and wastewater treatment facilities. Unlike passive components such as piping or static storage, mixers are dynamic machines responsible for facilitating chemical reactions, maintaining solids suspension, blending disparate fluid streams, and optimizing heat transfer. In the context of consulting engineering and plant operations, the selection of mixing equipment is a critical determinant of process stability, energy consumption, and long-term maintenance budgets.

In water treatment applications, mixing is the primary mechanism for rapid dispersion of coagulants during flash mixing and the gentle promotion of particle agglomeration during flocculation. The efficiency of these stages directly impacts downstream sedimentation performance and filter loading rates. Ineffective mixing here can lead to excessive chemical usage, increased sludge production, and potential regulatory violations regarding turbidity and disinfection byproducts.

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Wastewater treatment facilities rely even more heavily on robust mixing technologies. From maintaining suspension in equalization basins to optimizing biological environments in anoxic and anaerobic selector zones, mixers prevent septic conditions and facilitate nutrient removal. In activated sludge processes, mixers must balance the need for solids suspension with the requirement to avoid excessive surface turbulence that could strip oxygen or disrupt floc structures. Furthermore, sludge holding and digestion processes require specialized mixing to homogenize high-viscosity sludge, prevent thermal stratification, and maximize volatile solids reduction.

The regulatory environment, driven by the Clean Water Act and evolving NPDES permits, places increasing pressure on utilities to achieve lower nutrient limits (nitrogen and phosphorus) while simultaneously reducing carbon footprints. This dichotomy drives the engineering demand for mixing solutions that offer precise hydraulic control and high mechanical efficiency. OEM selection is therefore not merely a procurement exercise but a strategic engineering decision. The difference between a high-quality, application-engineered mixer and a generic alternative often manifests in lifecycle costs—specifically through gearbox reliability, impeller efficiency, and serviceability.

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This article provides a comprehensive technical analysis of the leading Original Equipment Manufacturers (OEMs) in the mixing equipment category. It is designed to assist consulting engineers, plant managers, and utility decision-makers in navigating the complexities of specification, application fit, and long-term asset management.

2. How to Select This Process Equipment

Selecting the correct mixing equipment requires a multi-dimensional engineering analysis that moves beyond simple horsepower ratings. Engineers must evaluate process requirements, hydraulic constraints, mechanical design standards, and maintenance accessibility. This section outlines the critical technical criteria for specifying mixing systems.

Process Function and Performance Requirements

The first step in selection is defining the process objective. Mixing applications generally fall into one of four categories: miscible liquid blending, solids suspension, gas dispersion, or heat transfer. In water and wastewater treatment, the primary metrics for defining these requirements are the Velocity Gradient (G-value) and tip speed.

• Flash Mixing: Requires high shear and high G-values (typically 700 to 1,000 s⁻¹) to instantly disperse chemicals. High-speed impellers with high power numbers are utilized here.
• Flocculation: Requires low shear and variable G-values (tapered from 60 to 20 s⁻¹) to build floc without shearing it. Large diameter, low-speed hydrofoil impellers are preferred.
• Solids Suspension: The goal is to generate sufficient bottom scour velocity to prevent deposition. Criteria are often specified as “uniform suspension” or “off-bottom suspension.” This is critical in equalization tanks and activated sludge basins.

Hydraulic and Process Loading Considerations

Tank geometry dictates the flow pattern. Engineers must evaluate the aspect ratio (liquid depth to tank diameter). A ratio greater than 1.0 may require dual impellers on a single shaft to prevent “dead zones” in the vertical profile. Additionally, the viscosity and specific gravity of the fluid are paramount. While municipal wastewater typically behaves like water, sludge storage and digesters involve non-Newtonian fluids with high viscosities, requiring high-torque gearboxes and larger impeller sweep diameters.

Baffling is another critical hydraulic consideration for top-entry mixers. Without baffles, a mixer in a cylindrical tank creates a solid-body rotation (swirling) rather than top-to-bottom turnover. Engineers must specify the correct number and width of baffles to convert rotational energy into vertical pumping capacity.

Materials of Construction

Corrosion resistance is non-negotiable. For municipal wastewater, 316 Stainless Steel is the standard for wetted parts (shafts and impellers). However, in aggressive industrial wastewater or chemical feed applications involving ferric chloride or alum, exotic alloys such as Hastelloy, Titanium, or vinyl-ester coated carbon steel may be required. Static mixers used in chemical injection often utilize PVC, CPVC, or PTFE-lined carbon steel depending on the chemical compatibility.

Integration with Upstream and Downstream Processes

The mixer does not operate in a vacuum. Its operation affects upstream head loss and downstream settling. For example, in anoxic zones, the mixer must keep biological solids in suspension without inducing surface turbulence that would introduce oxygen, thereby inhibiting the denitrification process. Integration with SCADA systems is also vital; modern mixers should be specified with vibration sensors, bearing temperature monitors, and leakage detectors that feed directly into the plant’s PLC for predictive maintenance.

Footprint and Layout Constraints

Retrofit projects often present severe space constraints. Top-entry mixers require structural bridges or heavy concrete slabs capable of withstanding significant torque and bending moments. In contrast, submersible mixers offer flexibility in positioning and can be mounted on guide rails, eliminating the need for overhead structures but requiring cranes or davits for retrieval. Side-entry mixers are efficient for large storage tanks but require wall penetrations that present long-term leakage risks if seals fail.

Energy Efficiency and Operating Cost

Mixing accounts for a significant portion of a plant’s energy bill. Engineers should specify premium efficiency motors (IE3 or IE4). More importantly, impeller design dictates hydraulic efficiency. Modern hydrofoil impellers can provide the same pumping capacity as older pitch-blade turbines with 30-50% less horsepower. Validating these claims requires reviewing the OEM’s pump curves and asking for CFD (Computational Fluid Dynamics) modeling verification during the submittal phase.

Operations and Maintenance Impacts

The “ragging” phenomenon in wastewater is the leading operational challenge. Stringy materials (wipes, hair, plastics) can wrap around impellers, causing imbalance, vibration, and seal failure. Engineers should prioritize OEMs offering “self-cleaning” or backswept propeller designs for raw sewage applications. Maintenance access is equally critical; gearboxes should be accessible without entering the tank, and submersible mixers must include reliable lifting mechanisms.

Common Failure Modes

Understanding failure modes aids in robust specification:

• Gearbox Failure: Usually caused by undersizing the service factor (AGMA) or inadequate lubrication monitoring.
• Shaft Deflection: Occurs when the operating speed approaches the critical speed (natural frequency) of the shaft. Engineers should specify shafts designed to operate well below the first critical speed.
• Seal Failure: Mechanical seals are the weak point of submersible and side-entry mixers. Double mechanical seals with barrier fluids are standard for submersibles to prevent moisture intrusion into the stator.

Lifecycle Cost Considerations

Low-bid procurement often results in higher lifecycle costs. A mixer with a slightly higher capital cost but a higher AGMA service factor gearbox and a more efficient impeller will save tens of thousands of dollars in energy and repair costs over a 20-year lifespan. Evaluations should include the cost of energy, oil changes, seal replacements, and expected overhaul intervals.

3. Comparison Table

The following table compares the locked list of OEMs based on their typical engineering applications and operational characteristics. Engineers should use this table to align project-specific requirements—such as tank geometry, fluid type, and maintenance capabilities—with the specific strengths of each manufacturer.

4. Top OEM Manufacturers

This section details the specific capabilities, technologies, and market positioning of the five manufacturers identified for the Mixing Equipment category. The analysis focuses on technical differentiators relevant to engineering specifications.

SPX FLOW (Lightnin)

Lightnin, a brand within SPX FLOW, is arguably the most recognizable name in the history of industrial and municipal mixing. Their engineering heritage dates back roughly a century, establishing many of the standards used in fluid mixing today. Lightnin is synonymous with top-entry and side-entry mixing configurations.

Technical Differentiators: Lightnin’s primary advantage lies in their impeller technology. The A310 and A510 hydrofoil impellers are industry benchmarks for flow-controlled applications like flocculation and solids suspension. These impellers are designed to maximize pumping capacity while minimizing shear and power consumption. For engineers, this translates to high process efficiency per kilowatt of energy input. Their gearbox technology is also notable; they offer purpose-built mixer drives rather than modified conveyor drives, ensuring the bearings and gears are rated for the significant bending moments and overhung loads inherent in mixing applications.

Application Focus: Lightnin excels in rapid mixing (flash mix) where high shear is required, and flocculation basins where gentle, uniform energy dissipation is critical. They are also a dominant player in anaerobic digestion, offering draft tube mixers and large linear motion mixers that handle high-viscosity sludge.

Philadelphia Mixing Solutions

Philadelphia Mixing Solutions (PMSC) has a reputation built on heavy-duty mechanical reliability and advanced testing capabilities. They maintain one of the world’s largest mixing laboratories, allowing them to validate CFD models with physical testing at significant scale. This reduces the risk for engineers designing complex or large-volume basins.

Technical Differentiators: The core of PMSC’s offering is the Raven gearbox series. Unlike standard industrial gearboxes, the Raven line is engineered specifically for the multidirectional loads of mixing. It features drywell construction to prevent oil leakage down the shaft—a critical feature for protecting water quality. PMSC also specializes in large-scale surface aerators and low-speed surface mixers for oxidation ditches, where mechanical longevity is the primary driver of lifecycle cost.

Application Focus: Philadelphia is often the preferred specification for massive biological basins, oxidation ditches, and applications requiring custom shaft lengths or exotic metallurgy. Their ability to retrofit existing tanks with upgraded drives and impellers makes them a strong candidate for plant rehabilitation projects.

Xylem Flygt

Xylem’s Flygt brand revolutionized the industry with the introduction of the submersible mixer. By placing the motor and impeller directly in the fluid, Flygt eliminated the need for long shafts and heavy support bridges, fundamentally changing how engineers layout anoxic and anaerobic zones.

Technical Differentiators: Flygt’s engineering strength lies in their submersible motor design and hydrodynamics. They offer a range of compact, direct-drive mixers for smaller tanks and large-diameter, low-speed “banana blade” mixers for maximizing thrust in large circulation loops. A key innovation is their “N-technology” hydraulics, adapted from their pump lines, which features backswept leading edges to shed fibrous material. This self-cleaning capability is crucial in raw wastewater and activated sludge applications where ragging is a constant maintenance headache.

Application Focus: Flygt is the standard-bearer for submersible applications. This includes nitrification/denitrification zones, sequencing batch reactors (SBRs), and sludge holding tanks. Their “Jet Mix” systems also provide an alternative for retention basins where floor-mounted equipment is undesirable.

Westfall Manufacturing

Westfall Manufacturing occupies a distinct niche in the mixing category: static mixing. Unlike the mechanical mixers discussed above, Westfall provides in-line engineered solutions that utilize the energy of the flow stream itself to achieve mixing. This approach eliminates moving parts, motors, and electrical connections.

Technical Differentiators: Westfall’s Low Head Loss Flow Conditioner (Model 3000) and Static Mixer (Model 2800) are engineered to generate high turbulence for mixing while minimizing pressure drop—a critical parameter in hydraulic profiles. Their designs often utilize vane-style mixing elements that create counter-rotating vortices. They also excel in materials engineering, offering large-diameter mixers fabricated from fiberglass (FRP) and various grades of stainless steel, making them highly resistant to corrosion in aggressive chemical feed lines.

Application Focus: Westfall is the go-to OEM for chemical injection points (chlorine, ammonia, coagulants) within piping systems. They are also used for blending water from different sources or for pH adjustment. Their solutions are ideal for confined spaces where installing a tank and mechanical mixer is not feasible.

Heron Innovators

Heron Innovators is a specialized OEM focusing on process intensification and specific hydraulic mixing challenges. While less of a “commodity” mixer manufacturer than Lightnin or Flygt, Heron provides engineered systems that solve complex problems related to suspension and separation.

Technical Differentiators: Heron’s technology often integrates hydraulic mixing with other process functions, such as Suspended Air Flotation (SAF). Their systems utilize specialized nozzle and pump configurations to create mixing energy. This approach allows for the conditioning of flow streams, particularly in high-strength wastewater or industrial pretreatment. By decoupling the mixing energy (pump-driven) from the tank geometry, they can offer control strategies different from standard mechanical agitation.

Application Focus: Engineers typically turn to Heron Innovators for difficult industrial wastewater applications, algae removal, or scenarios where standard mechanical mixing fails to provide the necessary gas-liquid interface or separation characteristics. They are often involved in retrofit applications aimed at improving the performance of existing infrastructure.

5. Application Fit Guidance

Matching the OEM to the application is critical for project success. While there is overlap, certain manufacturers have clear advantages in specific domains.

Municipal Water Treatment

For clean water applications, the focus is on precise chemical dispersion and gentle flocculation.

• Preferred OEMs: SPX FLOW (Lightnin) and Philadelphia Mixing Solutions are dominant in flocculation basins and flash mix tanks due to their mastery of low-shear, high-flow impeller designs.
• Chemical Feed: Westfall Manufacturing is the standard for inline injection and flash mixing within the pipe gallery, saving significant plant footprint.

Municipal Wastewater Treatment

Wastewater introduces solids, rags, and biological requirements.

• Anoxic/Anaerobic Zones: Xylem Flygt is heavily favored here. The ability to mount mixers on guide rails allows for easy layout changes and retrieval without draining basins.
• Oxidation Ditches: Philadelphia Mixing Solutions and SPX FLOW (Lightnin) excel in surface aeration and horizontal rotor technologies required for these large footprint processes.
• Sludge Digestion: For anaerobic digesters, SPX FLOW (Lightnin) offers specialized draft tube and linear motion mixers that handle high solids concentrations and prevent scum blanket formation.

Industrial Wastewater

Industrial applications often involve variable pH, high temperatures, and toxicity.

• High Strength/Corrosive: Heron Innovators and custom-engineered units from SPX FLOW are often required. Materials of construction (Hastelloy, Duplex SS) become the driving selection factor.

Retrofit vs. Greenfield

• Greenfield: Engineers have the luxury of designing bridges and tanks to accommodate top-entry mixers (SPX, Philadelphia), which generally offer longer MTBF (Mean Time Between Failures).
• Retrofit: Xylem Flygt is often the best fit for retrofits because submersible mixers do not require new concrete bridges or structural reinforcement of tank rims. Westfall is ideal for solving mixing problems in existing piping runs without major construction.

6. Engineer & Operator Considerations

Beyond the catalog specifications, the practical realities of installation, operation, and maintenance determine the success of the equipment.

Installation and Commissioning

Proper installation is the foundation of reliability. For top-entry mixers, laser alignment of the shaft is critical. Even minor misalignment can lead to vibration that destroys gearbox bearings and seals within months. For submersible mixers, the positioning and angle of the mixer are paramount. “Dead spots” in a tank will lead to solids deposition and septic zones. Commissioning should always include vibration baseline testing and amp draw verification across the full range of liquid levels.

Maintenance Access and Safety

Operators frequently cite accessibility as their biggest grievance.

• Top-Entry: Changing oil in a gearbox located over an open basin requires safety harnesses and careful planning. Drywell gearboxes are preferred to prevent oil contamination of the process.
• Submersible: While they eliminate overhead maintenance, they must be hoisted out for service. Guide rails must be robust (often stainless steel) to prevent bending over time. The power cable management is a common failure point; cables must be properly strain-relieved to prevent damage from mixer thrust.

Spare Parts and Obsolescence

Mixing equipment is expected to last 20+ years. OEMs like SPX FLOW and Philadelphia Mixing Solutions have massive install bases, ensuring that parts availability is generally high. However, custom gearboxes can have long lead times (12-20 weeks). Plant managers should stock critical spares—specifically mechanical seal cartridges and motor bearings—to avoid prolonged process downtime.

Operational Lessons Learned

A common operational mistake is running constant-speed mixers when Variable Frequency Drives (VFDs) could save energy. However, running a mixer too slow on a VFD can cause insufficient cooling of the motor (for TEFC motors) or insufficient torque to prevent ragging. Engineers must program the SCADA system with minimum speed setpoints to protect the equipment. Additionally, level interlocks are mandatory; a submersible mixer running unsubmerged will overheat and fail rapidly.

Long-Term Reliability Risks

The greatest risk to long-term reliability is changing process conditions. If a plant increases its solids loading or changes polymer types, the viscosity of the fluid may change, rendering the original mixer design inadequate. This often leads to gearbox overloads. Engineers should design with a safety factor (typically 1.5 to 2.0 service factor on the gearbox) to accommodate future process intensification.

7. Conclusion

The selection of mixing equipment for water and wastewater applications is a sophisticated engineering task that balances hydraulic performance, mechanical durability, and lifecycle economics. There is no single “best” OEM; rather, there are manufacturers whose strengths align best with specific process nodes.

For top-entry applications requiring precise shear control and massive pumping capacity—such as flocculation and digestion—SPX FLOW (Lightnin) and Philadelphia Mixing Solutions offer the robust mechanical lineage and R&D depth required for critical infrastructure. For flexible, footprint-conscious applications in biological treatment and sludge holding, Xylem Flygt’s submersible technology remains the industry standard, particularly where ragging is a concern.

For in-pipe mixing and chemical injection, Westfall Manufacturing provides unmatched simplicity and efficiency, while Heron Innovators offers specialized solutions for complex hydraulic conditioning challenges. By understanding the distinct engineering DNA of these OEMs, municipal and industrial decision-makers can specify systems that ensure process compliance and operational peace of mind for decades to come.