Image Credit: Grainger Industrial Supply | Weir Minerals | Griswold Pump Company

 

Turbine pumps are special types of centrifugal pumps which use turbine-like impellers with radially oriented teeth to move fluid. They are also referred to as vortex, periphery, or regenerative pumps. These pumps combine the high discharge pressures of positive displacement or multi-stage centrifugal pumps with the flexible operation of centrifugal pumps. Additionally, the flow rate of turbine pumps is not extremely variable with large changes in pressure like in most centrifugal pumps. They are preferred in applications where high head, low flow, and compact design are desired, such as in deep-well pumping.

 

Advantages

Disadvantages

  • Generates high head and high discharge pressure
  • Low flow rate
  • Better handling of gas-liquid mixtures
  • Tight internal clearances require clean (no-solids) liquids
  • Flow rate less variable with pressure change
  • Particularly susceptible to damage from improper assembly
  • Compact design
  • No easy way to adjust performance

 

 

Pump Operation

Turbine pumps are dynamic pumps, meaning they utilize fluid momentum and velocity to generate pump pressure. Specifically, they are centrifugal pumps, which generate this velocity by using an impeller to apply centrifugal force to the moving liquid. To learn more about selecting centrifugal pumps, go to the Centrifugal Pumps Selection Guide page on GlobalSpec.

 

The main difference between a turbine pump and a typical centrifugal pump is its impeller design. Compared to most centrifugal pumps, turbine pumps have smaller diameter impellers with rows of numerous small vanes. These vanes recirculate the fluid as it travels from the suction end to the outlet. Specifically, fluid enters at the edge of an impeller blade (not through the eye) and is accelerated not only tangentially in the direction of rotation, but also radially outward into the casing channel by centrifugal force. As the fluid strikes the casing wall it is redirected back onto an adjacent blade (vane) where additional energy is imparted.

 

Fluid flow of a turbine pump. Image Credit: Lytron | MTH Pumps

 

This recirculation has the same effect as a multi-stage centrifugal pump, since it adds energy to the fluid at multiple points in the system (see image right - Credit: Roth Pump Company). This is what gives turbine pumps their characteristic high head capability, and is also the reason that they are referred to as "regenerative" pumps.

 

Specifications & Performance

The primary specifications to consider when selecting turbine pumps for an application are flowrate, pump head, pressure, horsepower, power rating, outlet diameter, and operating temperature. These specifications are described in detail on GlobalSpec's Pump Flow page.

 

The Pump Flow page also describes the significance of pump performance curves in regards to determining a pump's capabilities. A turbine pump's performance curve may look something like this:

Image Credit: Roth Pump Company

 

This curve demonstrates the wide operating range of turbine pumps. This range is desirable in many applications where the head may vary greatly or is hard to determine.

 

For a typical centrifugal pump, head decreases with capacity and is inversely proportional to the required horsepower to drive the pump. But in turbine pumps (as shown above), the required power increases with increasing pump head. Therefore, the driving motor should be selected based on the highest head that the turbine pump develops. In addition, turbine pumps should not be operated against a closed discharge without a pressure relief valve, since power reaches a maximum at shutoff.

 

Materials & Features

Pumps are typically designed with a number of different materials. The base materials, which constitute the parts of the pump exposed to the pumped media and the outside environment, are the most important to consider. Fluid characteristics, pressure ratings, and operating environment factors should be considered when selecting these materials. 

  • Cast iron provides high tensile strength, durability, and abrasion resistance corresponding to high pressure ratings.
  • Plastics are inexpensive and provide extensive resistance to corrosion and chemical attack.
  • Steel and stainless steel alloys provide protection against chemical and rust corrosion and have higher tensile strengths than plastics, corresponding to higher pressure ratings.

Designs and features of turbine pumps provide different facets of capability and functionality that may be important to consider.

  • Balanced impellers - Turbine pumps with balanced or floating impellers generate very little axial thrust on the motor shaft, promoting longer bearing life.
  • Close-coupled - Close-coupled pumps have the pump end mounted directly on the motor shaft for a more compact design.
  • Double-sided impellers - Double-sided impeller design helps to reduce impeller wear by building pressure equally on both sides and creating a thin fluid film between the impeller and casing. This film also causes the impeller to self-adjust to its optimum axial position. (Double sided design shown right - Image Credit: Lytron)
  • Multi-stage - Multi-stage turbine pumps move the compressed fluid through multiple successive chambers or stages of pressurization. While most turbine pumps are single stage (one impeller and chamber) because of their high head impeller design, some implement multiple stages to generate even higher pressure levels.
  • Thermal overload protection - Some pump motors include devices which will shut the pump off if the motor becomes too hot or exceeds a certain temperature.
  • Self-priming - Certain turbine pumps may be design for self-priming or sealless operation, meaning they are constructed so they can create and maintain a sufficient vacuum level to draw fluid into the inlet with no external assistance.
  • Submersible - The motor on a turbine pump is typically above the liquid level, but some can be designed to be submerged in the media on a shorter drive shaft. 
  • Vertical orientation - Turbine pumps with a vertical orientation, also called deep well pumps, are designed to pump media vertically through the pump body. They are specially designed for pumping water from deep water sources such as wells, and are mainly used over other types of pumps in applications where the water surface fluctuates regularly(Image Credit: Grainger Industrial Supply).

 For more information on pump materials and other pump features, visit the Pump Features page on GlobalSpec.

 

Applications

Turbine pumps are used in clean liquid applications that demand high head, low flow, compact design, and flexible operation. They're used in a wide range of industrial applications such as cooling water circulators for lasers and other machines where high head is required. Turbine pumps are also found in small boiler feed services in bakeries, dry cleaners, breweries, and other commercial plants. The Pump Applications page on GlobalSpec provides a list of pump types designed for specific applications.

 

References

 

Lawrence Pumps - Regenerative Turbine Pumps

 

Lytron - Regenerative Turbine Pumps Introduction

 

MTH Pumps - Regenerative Turbine Principles

 

National Pump Company - Selecting a Vertical Turbine Pump (pdf)

 

PumpScout - Renegerative Turbine Pumps

 

Roth Pump Company - Little Pump - Big Head