Mixed Flow Pump for Desalination Plants

Table of Contents

• Introduction: The Water Scarcity Challenge and Sintech’s Solution
• What Is a Mixed Flow Pump?
• How Mixed Flow Pumps Work
• Key Features and Benefits
• Mixed Flow Pump Applications
• Mixed Flow Pumps in Desalination Plants
• Sintech’s Mixed Flow Pump Solutions
• Corrosion-Resistant Materials for Desalination
• Maintenance and Reliability
• FAQs 

Introduction

Freshwater is scarce – only about 3% of Earth’s water is drinkable, and nearly 40% of the global population lives within 60 miles of the coast. Desalination plants turn abundant seawater into potable water, but the process is energy-intensive and costly, largely due to the massive pumping requirements. High-capacity pumps must move vast volumes of corrosive seawater and brine through multi-stage treatment, and inefficiencies here drive up both operational expenditure (OPEX) and capital expenditure (CAPEX) for water producers. This is where mixed flow pump shine. Sintech Pumps offers purpose-designed mixed flow pumps that are built for desalination – they deliver very high flow rates at moderate head, use corrosion-resistant materials, and run efficiently 24/7. By addressing these pain points (massive flow, space constraints, and saltwater corrosion) with optimized mixed flow pump designs, Sintech helps desalination plants lower costs and improve reliability.

What Is a Mixed Flow Pump?

A mixed flow pump is a type of centrifugal pump that combines features of both axial and radial (centrifugal) machines. It uses a diagonal or mixed-flow impeller: the blades are angled so that they push fluid radially outward (like a centrifugal pump) and axially forward (like an axial or propeller pump). In effect, the flow path is conical, and fluid gains both velocity and pressure as it moves through the impeller. Mixed flow pumps are often called diagonal pumps for this reason. Compared to pure axial pumps (which produce very high flow at very low head) or pure radial pumps (which produce higher head at lower flow), mixed flow designs achieve a balance: very high flow rates with moderate head. This makes them ideal for moving large volumes of water without needing extreme pressure.

How Mixed Flow Pumps Work

A mixed flow pump operates like a standard centrifugal pump, but its impeller geometry is a hybrid. As the impeller spins, fluid enters at the center and is carried outward by centrifugal force. At the same time, the slanted impeller blades also drive the fluid axially along the shaft direction. In other words, each blade flings the water outward and forward simultaneously. When the fast-moving fluid exits the impeller, it enters a diffuser or volute casing, where its kinetic energy is converted into pressure energy. The result is a high-volume flow emerging from the pump outlet at increased pressure (head). This dual-action (radial + axial) means mixed flow pumps can turn motor power into fluid energy very efficiently when pumping seawater, brackish water, or other liquids.

• Dual thrust (radial + axial): Mixed flow impellers provide both thrusts, enabling high flow and decent pressure. 
• Flow direction: Water exits in a combined radial-axial direction (conical flow) rather than purely outward or purely parallel to the shaft. 
• Energy conversion: As in all pumps, velocity gained in the impeller is converted to pressure in the diffuser/casing, so the discharge pressure rises. 

Because the fluid is always under pressure at the impeller inlet (especially in submerged/vertical installations), mixed flow pumps are often self-priming and less prone to cavitation than comparable horizontal pumps. This makes them very reliable for raw seawater intake, where NPSH (net positive suction head) can be a concern.

Key Features and Benefits

Mixed flow pumps offer several advantages for desalination and other high-capacity water-handling needs:

• Very High Flow Rates: They efficiently move large volumes of water – ideal for seawater intake or recirculation. (Horizontal mixed flow pumps can handle up to 7,000 m³/hr, and vertical models even more.) 
• Moderate Head: While their head (pressure) is lower than pure radial pumps, it is sufficient for many stages of a desalination process without excessive power use. 
• High Efficiency: The combined axial-radial design yields high hydraulic efficiency, especially in the mid-flow range. This means lower energy consumption and operating cost. 
• Space-Saving Design: Vertical mixed flow pumps take up very little floor area (the pump is mostly below floor level). They deliver maximum flow through the floor or a sump, a big advantage when plant real estate is limited. 
• Self-Priming, Anti-Cavitation: Because the impeller is often submerged, vertical mixed flow pumps do not need priming and maintain a positive suction head. This virtually eliminates cavitation risk, protecting impeller surfaces from pitting. 
• Versatility & Solids Handling: Mixed flow pumps can handle a variety of liquids, including seawater and lightly contaminated or turbid water. Many designs use a semi-open or balanced impeller, which can tolerate suspended solids or sand (common in raw seawater intakes). 
• Robust Construction: Designs often include heavy-duty bearings and hydraulically balanced impellers for vibration-free, long-life operation. This durability is vital in 24/7 desalination service. 
• Rising-head Characteristic: Some mixed flow pumps can be tuned (via adjustable vanes or canister designs) to maintain stable flow even if the plant head changes. This adaptability is useful during start-up or backwash cycles. 

Together, these features mean mixed flow pumps move the volumes needed in a desalination plant reliably and cost-effectively, with a much smaller footprint than an equivalent axial pump array or multiple parallel pumps.

Mixed Flow Pump Applications

Beyond desalination, mixed flow pumps are used wherever very large flows at low-to-medium heads are needed. Common applications include:

• Seawater and Brackish Water Intake: Perfect for pumping raw feedwater from the ocean or aquifers into desalination pretreatment. 
• Desalination Plant Processes: They circulate seawater/brine through thermal stages or evaporators, handle recirculating cooling water, and pump wash water or effluent within RO/MED plants. Typical tasks include brine recirculation, feedwater transfer, and wash water pumping. 
• Cooling Water and Heat Rejection: High-volume cooling towers or condenser loops in power or process plants often use mixed flow or axial pumps, due to the need for massive flow with moderate heat. 
• Flood Control and Irrigation: Municipal or agricultural systems that must move large flows (e.g. river diversion, drainage canals) use mixed flow machines for their capacity. 
• Stormwater and Sewage: The ability to handle dirty liquids means mixed flow pumps serve storm drains, wastewater treatment inflows, and sewage lift stations. 
• Industrial Processes: In pulp & paper mills they move slurry or dilute pulp, and in desalination (or chemical plants) they circulate processed water with dissolved solids. 

In each case, the key is volume. Mixed flow pumps are often the go-to solution when a facility must move tens of thousands of gallons per minute (or thousands of cubic meters per hour) but does not need very high pressure. They fill the performance gap between axial pumps (for extreme volumes at near-zero head) and multi-stage centrifugals (for high head, lower flow). For example, Sintech’s Horizontal Mixed Flow Pump (SMF series) handles up to 7,000 m³/hr and 45 m head, while the Vertical Mixed Flow Pump (SVMF series) handles even higher flows (up to 44,000 m³/hr).

Mixed Flow Pumps in Desalination Plants

In a water desalination plant, large mixed flow pumps play several crucial roles in the process. Typically, seawater is first drawn in through intake structures, and this raw feed must be pumped into pretreatment filters. Later, within the plant, mixed flow pumps may circulate seawater/brine through multi-effect evaporators or thermal stages, handle brine blowdown, or move intermediate process streams (like product or reject in secondary membranes) at relatively low head.

• Intake Pumping: The very first stage in many desalination plants uses a vertical mixed flow pump in a suction well or sea chest. These pumps sit vertically in a wet well, so they are always flooded at the inlet. They can pull enormous flow without losing prime and are resistant to cavitation – ideal for pumping raw seawater. Sintech’s vertical SVMF pumps are engineered for exactly this: large flow, 3D-angled impellers, and a submerged inlet to ensure stable operation even if the sea level fluctuates. 
• Low-Pressure Transfer: After initial filtration, water must be transferred to high-pressure RO units or multi-effect distillation. Mixed flow pumps can be used to move brackish or seawater through heat exchangers or feed tanks at moderate pressure. For example, a horizontal mixed flow pump may be used to recirculate condensate or brine within an evaporator system, where flows are high but pressure needs are limited. 
• Brine Circulation: Desal plants often recycle brine to improve recovery. Mixed flow pumps are well-suited to recirculate concentrated brine at modest head, which helps reduce overall feedwater intake. 
• Backwash and Cleaning: Mixed flow pumps can supply large volumes of water for backwashing filters or cleaning membranes, ensuring efficient plant operation. 
• Integration with Other Equipment: In combined systems like R-O (Reverse Osmosis) and M-E-D (Multi Effect Distillation) plants, mixed flow pumps work in tandem with high-pressure multistage pumps (for the RO feed) and with smaller auxiliary pumps. They handle the “heavy lifting” of volume, letting other specialized pumps focus on pressure or chemical dosing. 

The key benefits in desalination are clear: high throughput and reliability. Sintech’s pumps for desalination plants are built to meet these needs, and they are explicitly marketed for both RO and MED technologies. 

Sintech’s Mixed Flow Pump Solutions

Sintech Pumps offers dedicated mixed flow pump models tailored for desalination. Our Vertical Mixed Flow (SVMF) series is designed for very high flow. These vertical pumps require minimal floor space (the discharge is directed along the shaft axis) and are always flooded at the impeller inlet. The impeller is submerged, eliminating priming issues and preventing cavitation. For example, a typical SVMF unit can deliver flows up to 44,000 m³/hr at heads up to 300 m. This makes them perfect as seawater intake pumps or large circulation pumps in thermal desal plants. Their construction (submerged impeller, positive suction) means they reliably deliver their rated performance at high efficiency.Our Horizontal Mixed Flow (SMF) series are single-stage pumps for large-volume transfer. They are robust and energy-efficient. Typical SMF pumps handle up to 7,000 m³/hr at 45 m head. Their impellers are semi-open and hydraulically balanced, which helps them manage moderately contaminated or saline water. These units are used wherever a high flow rate of clean or filtered water is needed on a horizontal line, such as in feedwater supply, backwash, or large-circulation duties. (See Horizontal Mixed Flow Pumps – SMF for details.)Beyond mixed-flow models, Our desalination portfolio includes double-suction split-case pumps for extreme volume (ideal for the very first seawater lift) and special pull-out units for high-pressure RO feed. But focusing on mixed flow, Sintech Pumps emphasizes low maintenance and longevity. Their designs feature heavy-duty bearings and balanced hydraulics for vibration-free running. Parts in contact with saltwater are made of corrosion-resistant alloys (see next section), and the pumps are built to Sintech’s high quality standards. 

Corrosion-Resistant Materials for Desalination

Seawater is highly corrosive (containing chloride, silt, marine life, etc.), so desalination pumps must use special materials. Sintech notes that pump components are chosen based on water salinity and temperature – often Duplex stainless steel or Super Duplex for wetted parts. Duplex steels have excellent strength and are much more resistant to seawater stress corrosion than standard stainless steel. Industry sources confirm this choice: In practice, Sintech’s centrifugal and mixed-flow pumps for desalination often have casings and impellers machined from Duplex. This handles the harsh environment – brine with up to 3.5% salt and possibly organics. Duple steels (like SS2205 or SS2507) resist pitting and crevice corrosion that plain 304/316 SS would suffer in seawater. For parts not touching water (shafts, fasteners), quality stainless steels or coatings may be used. The result is equipment that lasts for years with minimal corrosion problems.Besides materials, Sintech’s pumps also have robust sealing options (like dynamic seals) to avoid leaks. This protects bearings and keeps maintenance down. Overall, choosing the right metallurgy is as crucial as the pump design itself in a desalination plant – an improperly built pump could pit or fail in months, whereas a Duplex pump runs reliably for decades.

Maintenance and Reliability

Mixed flow pumps in desalination are designed for continuous heavy-duty service. Sintech emphasizes long life and low upkeep. For example, their pumps use heavy-duty bearings and hydraulically balanced impellers to reduce vibration and wear. Vertical mixed-flow pumps operate immersed, so they naturally run cooler and avoid cavitation damage. Horizontal models feature strong frames and pull-out designs for easy servicing. Some Sintech specialty pumps (like the UMOR series) boast 20,000+ hour lives and long intervals between overhauls.Routine maintenance is straightforward: ensure the pump intake remains clear of debris, check lubricants, and periodically inspect impellers and casings. Thanks to their simple impeller geometry and sturdy construction, mixed flow pumps generally need less maintenance than high-speed multistage pumps. Nonetheless, Sintech recommends regular performance checks and vibration monitoring to catch any drift from optimal efficiency. Proper installation (correct elevation, aligned connections) is also critical. With care, a mixed flow desalination pump from Sintech can serve reliably for many years, safeguarding plant uptime and water supply.Keep in mind: Correct installation and care are key to pump longevity. Sintech offers after-sales support and a worldwide network of service centers, so if any issue arises, spare parts and expertise are readily available.

Conclusion

In the rapidly growing world of seawater and brackish water desalination, mixed flow pumps play a vital role in ensuring efficient, reliable, and continuous operation. Their hybrid design delivers the ideal balance of high flow and moderate head, making them indispensable for the water desalination process—from seawater intake to brine recirculation.With decades of engineering expertise, Sintech Pumps continues to innovate with mixed flow submersible pumps, mixed flow centrifugal pumps, and corrosion-resistant mixed flow impellers built specifically for demanding desalination pump applications. Each product is designed for durability, performance, and minimal maintenance—helping desalination plants achieve consistent output and lower lifecycle costs.For custom-engineered mixed flow pump solutions tailored to your desalination plant process, contact Sintech Pumps today. 

FAQs

Q1. What are mixed flow pumps?

A mixed flow pump combines the working principles of axial and centrifugal pumps. Its mixed flow impeller moves water both radially and axially, creating a conical discharge path. This design allows for high flow and moderate head, making it ideal for seawater intake, irrigation, and water desalination plants. Common types include the mixed flow centrifugal pump and mixed flow submersible pump.

Q2. What kind of pump is used in desalination plants?

Desalination plants typically use mixed flow pumps and centrifugal pumps for seawater intake, transfer, and circulation. A mixed flow submersible pump is preferred for its efficiency and corrosion-resistant design. These pumps deliver large water volumes at moderate pressure, essential for the desalination plant process and energy-efficient water desalination operations.

Q3. What is the difference between radial flow and mixed flow pumps?

A radial flow pump moves liquid perpendicular to the shaft, producing a high head with low flow. A mixed flow pump, however, pushes fluid both radially and axially using a diagonal mixed flow impeller. This creates higher flow at moderate head, making it more suitable for desalination pump and mixed flow pump applications like seawater intake and irrigation.

Q4. What are three types of dosing pumps?

The main types of dosing pumps are diaphragm dosing pumps, piston dosing pumps, and peristaltic dosing pumps. These are commonly used in the water desalination process for precise chemical dosing—such as pH correction, anti-scalant, and disinfection—to ensure consistent water quality throughout the desalination plant process.