How to Select the Dredge Machine

Dredge machine is a kind of sand suction pump used to transport sand slurry to long distance. The centrifugal sand pump is the main kind type of dredge machine. The dredge machine has innovations in hydraulic design and structural design. The flow parts are made of abrasion-resistant high chromium wear-resistant alloy castings, which has the features such as high efficiency, energy-saving, wear-resistance, and reliable operation. Dredge machines are suitable for transporting medium that contains strong abrasion solid particles such as mortar, sand, gravel, pebble, slag, etc., the mixed solid-liquid concentration can reach 60%. Dredge machine is an ideal sand mining, sand pumping, and sand delivery equipment. Users can use single or multiple dredge machines in series according to the actual working conditions for long-distance construction.

The first step of dredge machine selection is effective communication with customers. There are many models of dredge machines with different shapes and structures, and different dredge machine types are suitable for different working conditions. The OCEAN PUMP engineers will select the suitable dredge pump after understand the following information.

1. The thickness of the sand layer.
2. Whether there are rubbish and large-grain stones.
3. How much mud is in the sand.
4. What is the sand amount needs to be extracted every day.
5. Discharge distance.
6. Working in rivers or lakes; whether there is a water source; whether it is necessary to build a sand dredger to carry dredge machine units; whether there is a power supply in the working area.

After detailed communication with the customer including the specific needs, the next step is to select the appropriate dredge machine for the customer according to the requirements. The prerequisite for selection must be a more in-depth understanding to the various types of dredge machines performance. Each type of dredge machine has its own advantages and characteristics. The better solutions is based on a deep understanding of the sand pump performance.

1. Six Type of Dredge Machines Structural Performance Characteristics

A. PNS Ship and Land Dual-purpose Sand Pump Structure Characteristics

1. PNS series sand pump is mainly composed of sand pump body, impeller, guard plate, sand pump cover, bracket and bearing components.
2. The material of dredge machine body, impeller and guard plate can be gray cast iron, cast steel, wear-resistant alloy, and non-metal wear-resistant materials, the user can choose according to the purpose when ordering.
3. The shaft seal of the sand pumping machine adopts packing seal, and high-pressure flushing water is added to the packing chamber to better ensure the normal operation of the dredge machine.
4. The rotation direction of the dredge machine is counterclockwise when viewed from the water inlet; the outlet of the dredge machine is on the right side of the horizontal direction when viewed from the water inlet. The outlet can be adjusted in a 360 degree range if required on site.

2. Submersible Slurry Pump Structural Characteristics

1. The whole slurry pump is a coaxial integrated structure of dry motor and sand pump. The motor is protected by a mechanical seal, which can effectively prevent high-pressure water and impurities from entering the inner motor cavity.
2. In addition to the main impeller, there is also a stirring impeller, which can stir the sludge deposited on the bottom of the water into a turbulent flow and then extract it.
3. The main flow parts such as impeller and stirring impeller are made of high wear-resistant materials, which are wear-resistant, corrosion-resistant, non-clogging. It has strong sewage discharge capacity and can effectively extract larger solid particles.
4. Not limited by suction depth, high slag suction efficiency and more thorough dredging.
5. No need to be equipped with auxiliary vacuum pump, lower investment.
6. No need to be equipped with auxiliary stirring or injection device, easier to operate.
7. The motor is submerged in the water, and there is no need to construct complicated ground protection and fixing devices, and the management is easier.
8. The stirring impeller directly contacts the deposition surface, and the concentration is controlled by the diving depth, so the concentration control is more free.
9. The submersible slurry pump directly dives into the water, no noise and vibration, and the site is more tidy.

3.  Gravel Pump Structural Characteristics

1. The gravel pump is composed of pump head, sealing components, bearing components, brackets, etc.
2. The flow parts (gravel pump body, impeller, front guard plate, rear guard plate, auxiliary impeller, stuffing box, etc.) are all made of high-strength wear-resistant alloy castings, which have good corrosion resistance. So it is suitable for conveying large particles and has long service life.
3. The gravel pump has the features of wide flow path, good cavitation performance, high efficiency, and abrasion resistance.
4. The lubrication method of the gravel pump adopts thin oil lubrication, and has a water cooling device, which prolongs the life of the bearing.
5. Transmission methods include V-belt transmission, elastic coupling transmission, and gear reduction box transmission. Use multiple speeds and multiple deformation methods to make the gravel pump run under the best conditions. It has high operating efficiency and can meet many kinds of harsh conveying conditions.

4. Multi-purpose Sand Suction Pump Structural characteristics

1. The pump body of DS series multi-purpose sand suction pump adopts internal and external double-layer metal structure, the sand pump casing is vertical and split, and the outlet position is installed in rotation at 45-degree intervals.
2. According to different working conditions, the shaft seal can be divided into auxiliary impeller shaft seal, packing shaft seal and mechanical seal.
3. Adopt closed impeller, good wear resistance and high sand pump efficiency.
4. The blades are generally in the form of 5 blades, with high head, suitable for long-distance transportation.

5. Vertical Sand Pump Structural characteristics.

1. Vertical sand pump is composed of pump body, impeller, guard plate, motor frame and bearing assembly, etc.
2. The shaft seal is rubber skeleton oil seal. The packing chamber seal is separated from the lower end bearing, and the oil seal prevents mud and sand from entering the bearing during the vertical sand pump working, thus prolonging the life of the bearing.
3. Viewed from the direction of the impeller inlet, the rotation of the vertical sand pump is counterclockwise.
4. The auxiliary impeller is used to reduce the back pressure of the impeller, reduce the axial force and prevent some debris from entering the seal cavity, protect the seal, reduce wear, and extend the life of the seal.
5. The flow parts are made of wear-resistant cast iron, which has high hardness, high strength, anti-abrasion, and the service life is 2-3 times longer than ordinary materials.
6. Generally combined with a high-pressure water pump to form a hydraulic filling unit to work together.

6. Large Flow Sand Pump Structural Characteristics.

1. The biggest advantage of large flow sand pump is its high output. Compared with other sand pumping equipment types, the large flow sand pump is designed with a wide flow path and large suction. Under the same power, the output will be higher than other sand pump types.
2. The flow parts are made of cast iron or alloy, with good wear resistance.
3. The large flow sand pump is relatively small in size, light in weight, flexible in operation, and can be applied to different complex working conditions.
4. Open impeller, no clogging, high over-flow performance, can extract different media.
5. There are many models from small to large, and they can be equipped with diesel engines or motors, with high efficiency and mature solutions.

We can intuitively judge the different external structure of each dredge machine type from the appearance, but the internal performance characteristics are different. Only by understanding the structural characteristics of each dredge machine can we accurately provide customers with the correct sand pump type. After understanding the customer’s working conditions and selecting the appropriate sand pump type, it is necessary to determine the basic parameters of the sand pump, such as flow velocity, head and other related parameters that determine the output and discharge distance.

6.1 Dredge Machine Performance Parameter.

A. Flow velocity.

flow velocity(m/s)= Volume flow(m³/h)/ Pipe cross-sectional area(m²)/3600

When the water contains sand, the flow velocity of the slurry in the pipeline must be ensured. Unlike the clean water pump, the flow velocity shouldn’t be too low or too high. If the flow velocity is too low, the sedimentation of sand particles will occur, which will cause the sediment concentration in the dredge machine cavity to increase sharply, causing the impeller to wear out quickly, and in severe cases, it will cause pipe blockage and sand pump blockage. If the flow velocity is too high, it will increase the pipeline loss, decrease the flow amount, reduce the drainage efficiency, and easily block the pipe and the dredge machine. Therefore, when designing and selecting, the actual flow velocity should match the pipe diameter. Generally, the flow velocity is 2~3m/s.

The basic principle of selecting the flow velocity.

1. When the specific gravity of the solid sand is larger, the flow velocity is higher, and when the specific gravity is smaller, the flow velocity is lower.
2. When the solid sand particles are larger, the flow velocity is higher, and when the particles are smaller, the flow velocity is lower.
3. The flow velocity is higher when the slurry concentration is higher, and the flow velocity is lower when the slurry concentration is lower.

B. Head

When choosing the dredge machine head, three parameters such as discharge height, pipeline loss, and head reserve are mainly considered:

a. Discharge height refers to the actual height difference.

b. Pipeline loss. Pipeline loss is greatly affected by the pipe inner diameter and the medium flow velocity. In addition, it is also affected by the pipe material (the inner wall friction coefficient), the slurry concentration, the slurry viscosity, the pipe length, the pipe bending condition, and the pipe fittings such as valves.

It can be seen from the table that the smaller the pipe diameter, the greater the pipeline loss; the greater the flow velocity, the greater the pipeline loss. Therefore, it is wrong to use multiple thin tubes instead of thick tubes of equal area.

c. Head reserve

The dredge machine pipeline loss is calculated according to the doubling of the pipeline loss in the clean water state, which is a conclusion drawn from experience. Therefore, for the uncertain working conditions design, it is also necessary to consider increasing the design reserve of the head.

6.2 Detailed case

The specific working conditions are as follows.

1. If the dry sand output is 60m³/h, consider the dredge machine flow Q≈330m³/h.
2. Vertical height difference △H=4m, pipeline length L=550m.
3. The proportion of slurry is 1.3.
4. No elbow in tentative pipeline.

The model selection is as follows.

A. About flow velocity V and pipe diameter

Average flow velocity according to formula

V= πDD(4Q) /3600=3.14×0.2×0.2(4×330)=2.92m/s

It is recommended to use pipelines with an inner diameter of 200mm for transportation.

B. About head.

Pipeline loss head

Hfl=0.016×D(L)×2g(VV)
=0.016×0.2(550)× 2×9.8(2.92×2.92)
=19.141m

In summary, the actual head

H=(Hfl+△H)×1.1=(19.141+4)×1.1
= 25.455m ≈26m

C. About model selection

a. The above-mentioned flow Q=330m³/h; head H=26m

Select dredge machine model: ZS200, Speed: n=1150r/min, Efficiency 60%.

b. Power

Known slurry specific gravity Sm=1.3.

According to the formula

Pm=102η(QHSm)/3.6 =102×0.6(330×26×1.3)/3.6
=50.626KW

The actual power of the dredge machine is based on the formula:

P=Pm×1.1=50.626×1.1=55.688KW≈75KW

D. In summary, OCEAN PUMP recommends as follows.

1. The dredge machine model is ZS200 large particle sand suction pump. Speed: n=1150r/min.
2. Equipped with motor: Y280S-4/75KW/380V, equivalent to 120 horsepower.
3. CRZ drive (belt connection with common base).
4. Adopt packing seal.
5. The flow parts are made of high chromium alloy A05 (ie KmTBCr27).
6. The maximum particle size allowed to pass is 127mm.
7. Dredge machine weight 1350kg; motor weight 562kg.

The dredge machine selection is a process of comprehensive consideration. Working conditions, customer needs, sand pump performance and many other factors affect the final dredge machine type. OCEAN PUMP is a professional manufacturer and supplier of high-quality sand pumps, slurry pumps, and sand dredgers. OCEAN PUMP technical team has been engaged in the development, matching and application of sand pump machine such as river dredging, sea reclamation, and tailings treatment since the 1990s. With rich experience, excellent technology, and thoughtful service, OCEAN PUMP has won the trust of users. The company has focused on sand pump machine for more than 20 years. It not only provides high-quality products and overall solutions for the industry, but also provides on-site installation services. Please feel free to contact us for plan design and equipment issues related to dredging and sand suction.