Very Low Specific Speed Centrifugal Pump—Hydraulic Design and Physical Limitations

Abstract

For low-flow and high-head applications, pump types such as progressive cavity or gear pumps are often used. However, centrifugal pumps are much more robust and wear resistant, and are beneficial if they can handle the rated head and flows. By challenging the limitations of low specific speed (Nq), centrifugal pumps can be made to handle a combination of low flow and high head, which previously required other pump types. Conventional centrifugal pumps have specific speed down to 10, while in this paper a design with specific speed of 4.8 is presented. The paper describes several iterative steps in the design process of the low Nq pump. These iterations were done one physical pumps, which were successively tested in a test rig. Motivation for each step is explained theoretically and followed up by discussion of the measured results. Four different geometries of the pump were tested, all of them manufactured by rapid prototyping in nylon material. A substantial question is how low the specific speed of a centrifugal pump can be. Limitations of low Nq pumps are discussed and new findings are related to volute cavitation. In addition, limitations due to disk friction, volute losses, leakage flow, and pump stability are discussed and show to limit the design space for the pump designer.

Effect of Splitter Blades on Performances of a Very Low Specific Speed Pump

“…The impellers are 3D printed using the Fused Deposition Modeling (FDM) technology with Nylon 12. This method and material were used for a pump with comparable specific speed with higher performances by Olimstad [7]. The volute casing is CNC-milled from 2 blocks to ensure smooth hydraulic surfaces.…”

“…Despite the certain constraints that LSS pumps suffer from, they have a wide range of applications, especially in the oil, gas, hydrocarbon [3,4] and even aerospace industry [5] and preferred to positive displacement pumps due to a simpler design, high speed operation and lower failure probability. The general performance and physical limitations of LSS pumps have been investigated by Kurokawa [6] and Olimstad [7]. Special design has also been proposed by Klas [8,9] where thick trailing edge replaced classic blading, or more recently by Wei [10] and Yang [11] who tested slit impeller blades on a pump with a specific speed n q = 5.7.…”

Improvement of the design of hydraulic transport devices for the transport of hydroabrasive media in the enrichment industry

“…1 shows fragments of a new and worn pump impeller. Hydroabrasive abrasion of ground pump parts is determined by the formula [14]:…”

Effect of blade layout on performance of low specific speed pump operating in turbine mode

“…At low specific speed, especially below n q = 10 the centrifugal pumps are of rare use [5]. The primary reason is their low efficiency.…”