Types of Impeller: Classification and Applications

The term "3 types of impeller" is common, but impellers can be categorized in several key ways. Here are the three most fundamental and useful classifications:

1. By Flow Direction (Most Common Classification)

This categorizes how the fluid moves through the impeller relative to its axis of rotation.

• Centrifugal (Radial Flow):

  • How it works: Fluid enters axially at the eye (center) and is accelerated outward radially (perpendicular to the shaft) by centrifugal force. It exits the volute casing at high pressure.

  • Characteristics: High pressure, moderate to high flow. The classic pump impeller.

  • Applications: Water pumps, industrial process pumps, HVAC systems, automotive coolant pumps.

• Axial Flow:

  • How it works: Fluid enters and exits essentially parallel to the shaft (axially), like a propeller. It pushes the fluid rather than throwing it outward.

  • Characteristics: Very high flow, low pressure lift.

  • Applications: Boat propellers, pumps for large volumes of water (irrigation, flood control), wind tunnels, ventilation fans.

• Mixed Flow:

  • How it works: A combination of radial and axial action. Fluid enters axially but exits at an angle (between 0 and 90 degrees) to the shaft.

  • Characteristics: A balance between flow and pressure. More efficient than radial for certain medium-head applications.

  • Applications: Large water circulation pumps, some wastewater pumps, irrigation.

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2. By Specific Application & Design (Common Real-World Examples)

This classification is based on their dominant use and mechanical features.

• Closed Impeller:

  • Design: Has a front and back shroud (wall) that fully encloses the vanes. This creates efficient, directed flow channels.

  • Advantages: High efficiency, good for handling clear liquids. Structurally strong.

  • Disadvantages: Can clog easily with solids. More expensive to manufacture.

  • Applications: Clean water pumps, chemical processing, high-efficiency HVAC pumps.

• Open Impeller:

  • Design: Vanes are open on both sides, attached only to a central hub.

  • Advantages: Resists clogging, can handle slurries and stringy solids. Easier to clean and inspect.

  • Disadvantages: Lower efficiency due to fluid recirculation. Structurally weaker; requires a tighter casing clearance.

  • Applications: Slurry pumps, wastewater/solids handling, pulp and paper stock.

• Semi-Open Impeller:

  • Design: A compromise. Vanes are attached to a back shroud but open on the front side.

  • Advantages: Better strength than open impellers, better solids-handling than closed. Adjustable clearance to maintain efficiency.

  • Applications: Moderately dirty liquids, some chemical processes, viscous fluids.

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3. By Suction Type

This refers to how fluid is admitted into the pump.

• Single Suction:

  • Design: Fluid enters the impeller from one side only.

  • Characteristics: Simpler design. Creates an axial thrust load that must be balanced by bearings or other means.

  • Applications: The most common type for standard centrifugal pumps.

• Double Suction:

  • Design: Fluid enters the impeller from both sides simultaneously. The impeller is essentially two single-suction impellers back-to-back.

  • Characteristics: Hydraulically balances axial thrust, reducing bearing load. Allows higher flow rates. Often larger and more expensive.

  • Applications: Large water supply pumps, high-capacity service pumps.

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Quick-Reference Comparison Table

In summary, when someone asks for "3 types," they most often mean Centrifugal Impeller, Axial, and Mixed Flow (the flow direction classification). However, knowing the distinctions between Closed, Open, and Semi-Open designs is equally critical for practical selection.