What are the common structural forms of long-axis pump impellers

Long-shaft pumps are a type of vertical pump widely used in power plant cooling water systems, municipal drainage projects, the petrochemical industry, and large-scale industrial circulating water processes. One of their core components is the impeller. As a key component in energy conversion, the impeller directly determines the pump's hydraulic performance, efficiency, and applicable operating conditions. Long-shaft pumps utilize different impeller structures to meet flow rate, head, liquid characteristics, and operational stability requirements. Common long-shaft pump impeller structures include open, semi-open, closed, and mixed-flow impellers.

Open Impeller

Open impellers consist of blades and front and rear hubs, lacking complete front and rear shrouds, resulting in a relatively simple structure.

Open impellers are particularly well-suited for conveying media containing large amounts of solid particles or impurities. Because the impeller's open channel is less susceptible to clogging by impurities, the fluid passes through with minimal resistance, making it suitable for conveying sewage, slurries, and fibrous materials.

Among long-shaft pumps, open impellers are commonly used in municipal drainage projects, sewage treatment plants, and some seawater intake pumps. Its advantages include strong adaptability to media and easy maintenance, allowing for direct blade grinding or trimming during maintenance. However, its disadvantages are lower efficiency compared to closed impellers and the impeller is prone to wear over extended periods, which can affect the pump's long-term stability.

Semi-open impeller

A semi-open impeller is an open impeller with an additional cover, typically a rear cover or a partial structural cover. It combines the advantages of both open and closed impellers, ensuring good flow capacity while also improving hydraulic efficiency.

Semi-open impellers are commonly used for conveying media containing small amounts of solid particles, fibers, or gases. Typical applications include circulating water pumps in chemical plants, slurry pumps in the papermaking industry, and some seawater pumping stations.

In the long-shaft pump sector, the advantage of a semi-open impeller is its relatively spacious passageway, which effectively reduces the risk of clogging. It also offers higher operating efficiency than open impellers. However, its disadvantages are the high requirements for installation precision and impeller clearance. Improper clearance adjustment can lead to reduced efficiency and wear on the pump body.

Closed Impeller

A closed impeller consists of a front shroud, a rear shroud, and blades, completely enclosing the flow path. It is the most common impeller type. It offers optimal hydraulic performance, high efficiency, and minimal energy conversion losses, making it widely used for conveying clean water or low-solids media.

In long-shaft pumps, closed impellers are often used in power plant cooling water circulation, industrial circulating water, and large-scale clean water intake projects. Their advantages include high efficiency, low energy consumption, and stable performance over long periods of operation.

The disadvantage of closed impellers is that they are not suitable for media with high impurities or fibrous contents due to the relatively narrow flow path, which can easily clog. Furthermore, they are costly to manufacture and require strict installation and maintenance. Closed impellers are the preferred choice for applications requiring long-term, efficient operation and conveying clean media.

Mixed Flow Impeller

A mixed flow impeller is a special impeller that combines centrifugal and axial propulsion, with its fluid outlet direction intermediate between centrifugal and axial flow. This structure can operate under low-head, high-flow conditions and is commonly used in power plant circulating water pumps, agricultural irrigation pumps, and large-scale water intake projects.
The mixed-flow impeller is characterized by high efficiency and is suitable for conveying large quantities of clean water or water with minimal impurities. Its advantages lie in its rational structure and stable operation over a wide range of operating conditions, making it particularly suitable for applications with relatively low heads but high flow requirements.
In the long-shaft pump sector, the mixed-flow impeller offers excellent hydraulic performance, reducing energy loss and improving overall pump efficiency. However, its disadvantages are that it is not suitable for applications requiring high heads and is susceptible to damage in media containing large solid particles.

Axial-flow impeller

In addition to the above types, axial-flow impellers are also used in long-shaft pumps depending on the operating conditions. Axial-flow impellers are similar to propellers, with liquid flowing primarily along the axial direction. This type of impeller is suitable for extremely high flows and ultra-low heads and is commonly used in flood control and drainage pumping stations, seawater intake pumping stations, and large-scale agricultural irrigation systems. The advantages of axial flow impellers are large flow, low energy consumption, and adaptability to low head conditions. Its disadvantages are limited adjustment range and unsuitable for conveying media containing large amounts of solid impurities.