Flexible Impeller Pump

Introduction of Flexible Impeller Pump

A Flexible Impeller Pump is a type of positive displacement pump that employs a soft, pliable elastomer impeller with a series of curved blades. During operation, the impeller deforms as it rotates within a closely fitted casing, creating a series of expanding and contracting cavities. This action draws fluid into the pump at the suction side and expels it at the discharge side, achieving self-priming and gentle handling capabilities.

Ideal for a variety of fluids including those with particulates, these pumps excel in applications requiring variable flows, low shear, and the ability to handle entrained air or gases. Their versatility spans industries such as marine, food processing, and chemical, where the pump’s inherent flexibility ensures efficient and reliable fluid transfer even under challenging conditions.

Working Principle of Flexible Impeller Pump

The flexible impeller pump operates on the principle of positive displacement, using an elastomeric impeller that is designed with a series of curved and folding blades. Here’s a step-by-step description of how it works:

  1. Impeller Design: The core component of this pump is a flexible impeller made from rubber or similar material. It has a helical shape that allows it to compress and expand along its length.

  2. Suction Phase: When the pump starts rotating, the flexible impeller, housed within a close clearance housing, initially expands as it moves away from the suction inlet. This expansion creates a vacuum which pulls fluid into the pump chamber.

  3. Displacement: As the impeller continues to rotate, it passes through the narrowest part of the pump casing. At this point, the blades are compressed by the casing walls, reducing the volume inside the chamber and thus forcing the trapped fluid out of the pump.

  4. Compression and Discharge: The compression of the impeller blades effectively squeezes the fluid out through the discharge port. The high degree of conformity between the impeller and the casing ensures minimal slip, enabling the pump to maintain good volumetric efficiency.

  5. Self-Priming and Air Handling: The ability of the impeller to collapse and reform makes the pump self-priming. It can evacuate air pockets from the suction line and can also tolerate and pass small amounts of entrained air or gas bubbles without losing prime or causing damage.

  6. Gentle Handling: Because the impeller is soft and pliable, it can handle viscous fluids, liquids with suspended solids, and shear-sensitive materials with minimal damage to their integrity.

Overall, flexible impeller pumps provide smooth, low-shear pumping action that is gentle on delicate fluids while still being able to deliver consistent flow rates. They’re often used in applications where other types of pumps might struggle due to the nature of the liquid being pumped or the need for frequent start-stop operations.

Flexible Impeller Pump - SeFluid


Power: 0.37-1.5 kw
Capacity: 30-200 L/m
RPM: 1400
Flow Head: 20-30 m


Flexible impeller pumps offer several distinct advantages over other types of pumps, making them a preferred choice in certain applications. Here are some key advantages:

  1. Self-priming Ability: Flexible impeller pumps have excellent self-priming capabilities, meaning they can evacuate air from the suction line and draw liquid from a source located above or below the pump itself. This eliminates the need for external priming devices.
  2. Gentle Fluid Handling: The soft and pliable nature of the elastomeric impeller minimizes shear forces on the fluid being pumped. This characteristic is particularly valuable when handling delicate or shear-sensitive fluids like emulsions, suspensions, and biological materials.
  3. Versatility in Viscosity: These pumps can handle a wide range of fluid viscosities, from thin liquids to relatively thick fluids, and they can do so efficiently without significant loss of flow rate.
  4. Efficient With Particulates: They can pass small solids and particles present in the fluid without clogging, which is beneficial for applications involving slurries or liquids with suspended solids.
  5. Variable Flow Rates: By changing the speed of the pump motor, the flow rate can be adjusted easily without significantly affecting the pressure output, offering precise control over fluid delivery.
  6. Low Maintenance: Due to their simple design and few moving parts, flexible impeller pumps generally require less maintenance than many other pump types.
  7. Ease of Repair: If the impeller does wear down or become damaged, it can often be replaced quickly and inexpensively, minimizing downtime.
  8. Quiet Operation: They operate more quietly compared to some other pump types due to the cushioning effect provided by the flexible impeller.
  9. Compact Size: These pumps tend to be compact and lightweight, making them ideal for installations where space is limited.
  10. Adaptability: Flexible impeller pumps can work in both forward and reverse directions, providing additional flexibility in system design and operation.

These features make flexible impeller pumps a popular option in industries such as food processing, marine, pharmaceuticals, cosmetics, and many others where fluid compatibility and gentle handling are paramount. However, it’s important to note that they may not be optimal for high-viscosity fluids or those containing large solids, and their lifespan can be affected by aggressive or abrasive liquids.

Fluid Types Suitable for Flexible Impeller Pumps

Flexible impeller pumps are designed to handle a variety of fluid types, especially those that require gentle pumping action, self-priming capabilities, or the ability to process liquids with varying viscosities and small particulates. Here are some common fluid types suitable for flexible impeller pumps:

  1. Thin Liquids: Water, solvents, alcohols, light oils, and other low viscosity fluids can be transferred efficiently by these pumps.

  2. Viscous Fluids: While not optimized for extremely viscous fluids, flexible impeller pumps can manage moderate viscosities such as glycerin, syrups, and certain paints, varnishes, and coatings.

  3. Sensitive Fluids: Because of their gentle pumping action, they are well-suited for delicate fluids that might be damaged by shearing forces, including food products (like fruit juices, dairy products, and sauces), pharmaceuticals, cosmetics, and biochemical solutions.

  4. Emulsions: They can handle stable emulsions like milk, mayonnaise, or various chemical emulsions where maintaining homogeneity is crucial.

  5. Suspensions: Flexible impeller pumps can accommodate fluids with small suspended solids, like slurries with fine particles, although they are not recommended for large or abrasive solids.

  6. Chemicals: Depending on the elastomer material used for the impeller, they can pump mild chemicals and detergents. For harsher chemicals, the pump must be made of compatible materials that resist corrosion and degradation.

  7. Fuel Transfer: In the marine industry, flexible impeller pumps are commonly used for transferring diesel, gasoline, and other fuels.

It is essential to ensure that the pump’s construction materials, including the impeller, casing, and seals, are compatible with the specific fluid being pumped. Additionally, while flexible impeller pumps can handle small amounts of entrained air, they should not be run dry for extended periods, as this can damage the impeller. Always consult the manufacturer’s specifications to confirm the suitability of a flexible impeller pump for any given application.


Flexible impeller pumps have a broad range of applications across different industries due to their unique properties and versatility. Some of the prominent applications include:

  1. Marine Industry: These pumps are widely used in marine applications for bilge pumping, fuel transfer, engine cooling systems, and waste disposal. Their self-priming ability and capacity to handle liquids with entrained air make them ideal for boat and shipboard use.
  2. Food & Beverage Industry: Flexible impeller pumps are perfect for transferring delicate foodstuffs like fruit juices, dairy products, wines, and spirits. They can handle viscous and shear-sensitive fluids without damaging their structure, flavor, or nutritional content.
  3. Pharmaceutical & Biotech: In these sectors, the gentle pumping action of flexible impeller pumps is crucial for transporting sensitive biological materials, active pharmaceutical ingredients (APIs), and formulated drugs without causing degradation.
  4. Cosmetics: They are utilized for transferring creams, lotions, and other personal care products, ensuring the formulations remain stable and intact.
  5. Chemical Processing: Although not suitable for all chemicals, they can handle certain mild chemicals, emulsions, and slurries where gentle mixing and pumping are required.
  6. Automotive: They are employed in vehicle manufacturing and maintenance for coolant circulation, oil transfer, and windshield washer fluid systems.
  7. Industrial Processes: Flexible impeller pumps can be used in processes that involve the movement of liquids with varying viscosities, temperatures, and suspended solids, such as paint, ink, adhesives, and lubricants.
  8. HVAC Systems: They can be utilized in heating, ventilation, and air conditioning systems for circulating water or refrigerants.
  9. Agricultural Sector: For spraying pesticides, fertilizers, and other agricultural chemicals, flexible impeller pumps can provide the necessary pressure and gentle handling.
  10. Water Treatment: They can be used in wastewater treatment plants for transferring sludge or effluent with small suspended solids.

Always consider the specific requirements of each application and verify that the pump materials are compatible with the fluids being handled. The selection of the right flexible impeller pump is critical to ensure optimal performance and longevity in each unique setting.

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