Learn - Jun. 01, 2023
Major water conservancy projects include many trans-watershed water diversion projects. These diversion projects take water from rivers and lakes and transfer it to where it is needed. In temperate climates, the water levels of rivers and lakes change with the seasons. Therefore, the head of water pumps of the water diversion projects should be changed accordingly. Diagonal flow pumps are used extensively in water diversion projects. The features of a diagonal flow pump is the wide range of applicable head.
A Diagonal Flow Pump is also known as a guide vane mixed flow pump, also known as an adjustable blade guide vane mixed flow pump. It is vertical single stage structure, a typical large diameter large capacity vertical pump.
In water conservancy projects, especially the water pump used in water diversion projects, the head changes greatly with the season, and the performance of diagonal flow pumps change greatly with the difference of blade Angle, which are suitable for water diversion projects to adapt to the change of head.
Large diameter axial flow pumps and centrifugal water pumps are also commonly used in water conservancy projects. An axial flow pump is suitable for large capacity and low head conditions. The advantages of axial flow pump are simple structure, small volume, easy installation, and the disadvantage is that the performance is unstable in the small flow area. If the flow rate decreases, the shaft power would increase sharply. Therefore, the high efficiency range of an axial flow pump is narrow, not suitable for use in the occasion where has great changes of head.
| Diagonal Flow Pump | Axial Flow Pump |
| Head (over 20 m) | Head (below 10m) |
| Suitable for wide range of head changes | Suitable for narrow range of head changes |
| The head curve is flat. No obvious saddle-type. It could operate near the closing point. | The head curve has saddle-type. It couldn’t operate near closing point. |
| The high efficiency zone covers a wide range. | The high efficiency zone covers a narrow range. |
| Suitable for a wide range of flow. It could be continuous operation at low flow rate. | It could be intermittent operation at low flow rate, and need to start and stop frequently. |
The diagonal flow pump is a kind of pump whose structure and performance is between the axial flow pump and the centrifugal pump, with the advantages of the axial flow pump and the centrifugal pump, avoid their disadvantages, is the ideal pump in the water conservancy project. The application of diagonal flow pump is expanding to the field of the centrifugal pump and the axial flow pump. Diagonal flow pumps have features of small outer diameter structure, convenient maintenance and disassembly, strong cavitation resistance and high efficiency, especially suitable for the water level change larger, higher head requirements of the occasion.
Adjustable angle blades are divided into semi-adjustable blades and fully-adjustable blades:
When the semi-adjustable blade Angle needs to be adjusted, loosen the fastening screw of the blade, rotate the blade to the required Angle, ensure that the placement Angle of each blade is consistent, and then tighten the screw to achieve the purpose of changing the running condition.
For the fully-adjustable blade, under the conditions of stop or non-stop, adjust the mechanism through mechanical or hydraulic device, making blades rotate to meet the requirements of flow and head performance.
The characteristics of diagonal flow pumps: wide range of head change, high efficiency, wide range of high efficiency, head performance curves flat, could operate near the closing point, adjust the blade Angle, the gap between the hub and the blade is not affected, making the application of diagonal flow pumps more and more wide. Water conservancy project, substation circulation and cooling system, propulsion machinery sprinkler system, sewage treatment, seawater desalination, etc.
In the water diversion project, Baoying Station, the design head is 7.6 meters, the diagonal flow pump operation effect is very good, the test efficiency is more than 80%. Shanghai Qingcaosha Pump Station, designed lift 5.8 meters. Big diameter diagonal flow pumps were used at Ju Ning and Hongze pump stations. In 2022, the Shushan Hub Project, located in Anhui section, would have a total installed capacity of 60,000kW, a single power of 7,500kW, equipe with 8 vertical fully-adjustable guide vane mixed flow pumps with impeller diameter of 3480mm and designed flow rate of 340m³/s. Upon completion, the project will be Asia's largest installed and discharge mixed-flow pump station.
