Working Principle and Performance Characteristics of Mixed-flow Pumps

A mixed-flow pump conveys liquid by virtue of the combined action of centrifugal force and axial thrust, hence the name "mixed-flow pump".

Working Principle of Mixed-flow Pumps

In terms of working principle, when the prime mover drives the impeller to rotate, its action on the liquid involves both centrifugal force and axial thrust—a combination of the operating mechanisms of centrifugal pumps and axial-flow pumps. Therefore, it is a type of pump that falls between centrifugal pumps and axial-flow pumps.

The specific speed of mixed-flow pumps is higher than that of centrifugal pumps but lower than that of axial-flow pumps, generally ranging from 300 to 500. Its head is higher than that of axial-flow pumps but lower than that of centrifugal pumps; its flow rate is lower than that of axial-flow pumps but higher than that of centrifugal pumps.

Mixed-flow pumps are mainly used for agricultural irrigation and drainage. Additionally, they are applied in urban drainage systems and can serve as circulating water pumps in thermal power plants.

Performance Characteristics of Mixed-flow Pumps

High and Wide Efficiency RangeMixed-flow pumps feature high efficiency, and their high-efficiency operating range is relatively broad. This allows a single pump to operate economically even when there are significant variations in head or flow rate.

Stable Power OutputThe power output of mixed-flow pumps changes minimally from the low-flow point to the high-flow point. The pump can be started either at the closed valve point or at the maximum flow point (fully open valve), which facilitates the matching of supporting power units.

Excellent Suction PerformanceMixed-flow pumps have good suction capacity. For small and medium-sized pumps, they can be installed at a relatively high position above the water level, making operation, management and maintenance convenient. For large-scale pumps, this characteristic can reduce excavation depth and cut down pumping station construction costs, while eliminating the risk of cavitation during operation.

Structural Features

Volute-type mixed-flow pumps share structural similarities with centrifugal pumps.

Large-scale adjustable-blade volute-type and guide-vane-type mixed-flow pumps offer stable operation, high economic benefits, simple operation and a wide application range. However, their structure is complex, comparable to that of large-scale adjustable-blade axial-flow pumps.

Large-scale mixed-flow pumps equipped with front guide vanes also have unique advantages, such as safe and reliable operation and low operating costs within a certain specific speed range. Their structural complexity is lower than that of adjustable-blade types.

Particularly in large pumping stations where head variations are not significant, the adoption of vertical volute-type fixed-blade mixed-flow pumps yields multiple benefits, including simple structure, high efficiency, convenient operation and maintenance, and low investment costs.