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Working States of High Pressure Dredge Pump at Different Conveying Distance

High-Pressure Dredge Pump

A high-pressure dredge pump is a powerful and specialized device designed for efficient and effective sediment removal in various industries, including mining, construction, and marine operations. This type of pump is engineered to handle the demanding task of extracting solid materials from underwater or ground surfaces with significant force and precision.

The primary function of a high-pressure dredge pump is to create a strong vacuum that suctions in sediments, such as sand, silt, gravel, and rocks, from the bottom of water bodies or excavation sites. These pumps are typically mounted on dredgers, barges, or other vessels, and they play a crucial role in maintaining waterways, harbors, and channels by ensuring proper depth for navigation, as well as in land reclamation projects.

The high pressure dredge pump can realize conveying distance of over 500 meters, or even 3000-4000 meters. When selecting the pump, the engineers of Tai’an Ocean Pump consider the impeller with large outer diameter, and design the flow channel width according to the production requirements and the solid particle size. So, what’s the real working states of the high pressure dredge pump at different pump head? Users usually have some misunderstandings or confusion. Let’s discuss about that in this text.

Is the pump flow of the high pressure dredge pump will increase as much as they want when they shorten the pipeline enough?

For the same power unit and the same pipeline diameter, is the closer the delivery the farther the slurry spraying and the greater the pump flow?

Is it possible to increase the flow just by increasing the rotating speed?

In fact, these are not correct. The below example will help you to understand these questions.

Is the pump flow of the high pressure dredge pump will increase as much as they want when they shorten the pipeline enough?

Taking ZS400 high pressure dredge pump as an example, the working condition and the customer’s requirements are as follows. Pump flow: 1800 m³/h, conveying distance: 900 m, inner diameter of the pipeline :400 mm, height difference:1-2 m, sand quality: mainly medium sand with a small amount of small pebbles, driven by diesel engine.

According to the above requirements, our engineers calculated the data and considered the allowance, designed the clear water flow of 2000 m³/h. Then calculated the resistance loss along the 900 m conveying distance, that is 32.69m. According to the performance curve of ZS400 high pressure dredge pump, we got the operating point with 450 rpm, 2000 m³/h flow, 34 m pump head, 4m NPSH and 65% efficiency. With the chosen pump flow, pump head and efficiency, the shaft power of the pump can be calculated, that is 284.9kw. Considering the limit working state of the pump, referring to the maximum shaft power of 424.84kw at the same rotating speed. According to the above calculation, the requested engine power should be not less than 693.3hp. Finally, WEICHAI 818hp / 1350rpm marine engine and a set of 3:1 gearbox were selected.

After the ZS400 high pressure dredge pump arrived at the worksite, the user connected a 10 m pipe for water test first. He found that the starting flow was very large, and the diesel engine speed was about 900 rpm. Then they increased the engine speed to 1000 rpm. The pump suddenly vibrated. The flow became half of the beginning and the flow was not stable. The pressure gauge at the pump outlet show a very low data. The customer thought that there might be some leakage of the pipeline. So they checked the pipeline and high pressure dredge pump again. No air leakage or blockage were found.

The customer fed back the operation video and pressure gauge values to the engineer of Tai’an Ocean Pump. Through communication and judgment, the engineer gave the explanation as bellow: ZS400 high pressure dredge pump is designed for the long distance convey. When the high pressure pump was running at the low pressure working conditions, the flow will be very large. And when it exceeds the reasonable range, there will be cavitation. The cavitation produces great impact force, greatly reduces the pump efficiency and the pump flow. Numerous bubbles generated, expanded, burst rapidly, which caused the pump vibration。

As shown in the curve below, the working point for 900 m convey distance is at A. At point A, the pump flow is 555 L / S (2000 m 3 / h), the pump head is 34 m, the pump speed is 450 RPM, the efficiency is 65%, and the NPSH is 4 m. But when the client was testing the machine, the pipeline was only 10 meters, and the requested pressure for 10 m conveying was much smaller than that for 900 m conveying. So, the actual pump flow was too big and exceeded point B. The NPSH was more than 9m. Which caused cavitation easily, then flow dropped instantly and the pump didn’t work normally.

How to test the pump unit before connecting all the pipeline?

Testing the performance of a high-pressure dredge pump before connecting all the pipelines is a crucial step to ensure its proper functioning. In situations where the pipeline is too short and fails to generate sufficient resistance, the pump may struggle to achieve the desired pressure and flow rate. Fortunately, there is a solution to overcome this challenge.

To test the pump unit under such circumstances, it is recommended to assemble a gate valve at the end of the pipeline. The gate valve serves as a control mechanism to regulate the pressure within the pipeline. By adjusting the opening and closing of the gate valve, the operator can manipulate the resistance within the system.

During the testing process, the operator should monitor the outlet pressure gauge closely. As the gate valve is gradually closed, the resistance within the pipeline increases, and the pressure within the system builds up. The goal is to reach a pressure of 0.3 MPa (megapascal) as indicated by the outlet pressure gauge.

Once the pump unit achieves the desired pressure of 0.3 MPa, it signifies that the pump is operating effectively, and its performance can be adequately evaluated. This testing method allows for the assessment of the pump’s pressure and flow rate capabilities, ensuring that it meets the intended design specifications.

By conducting this preliminary test, operators can identify any potential issues or inefficiencies in the pump’s performance before connecting all the pipelines. It provides an opportunity to make adjustments or troubleshoot problems, guaranteeing that the pump unit is ready for optimal operation once the complete pipeline system is installed.

In summary, by incorporating a gate valve at the end of the pipeline and controlling the pressure through its opening and closing, operators can test the performance of a high-pressure dredge pump even when the pipeline is too short to generate sufficient resistance. Achieving a pressure of 0.3 MPa indicates the successful functioning of the pump unit, ensuring its readiness for the subsequent pipeline connections.

Conclusion

Therefore, we have to design the pump unit according to the actual working condition. It’s impossible to use the same pump for long conveying distance, near conveying distance, big flow and small flow construction conditions. The low pressure pump mainly focuses on large flow. If it is used for long distance transportation, it may cause pipe blockage due to low pressure and slow flowing speed. When the high pressure dredge pump works at a low pressure point, cavitation occurs and the pump can’t work normally. The pump flow of high pressure dredge pump can increase infinitely for short distance conveying, this is actually a big misunderstanding.The working condition of low pressure and high pressure dredge pump should be accordance with their designed flow and head. Improper use will decrease output and efficiency.