The river mud contains more water and has good fluidity, so that is not necessary to make additional slurry when dredging. The small underwater dredging pump can be directly hoisted into the water to pump mud and sand, or the centrifugal underwater dredging pump that connects with suction hose can be installed on the boat, the bottom end of the suction hose is equipped with a bottom valve filter which is put into the water to pump sediment. For more viscous working conditions, the medium can also be diluted with a water gun and discharged with a underwater dredging pump.

A fire power company in Guizhou undertook the flood drainage ditch dredging project. The flood ditch is 400m long, 5m deep, 5m wide, the water is 2m deep, and the silt is -1.6m deep. They selected the ZJQ100-50 37kW centrifugal underwater dredging pump, the dredging pump was placed in the trolley on the shore for the dredging work. The centrifugal underwater dredging pump is connected with a 15-meter-long suction hose, and the bottom valve filter connected to the suction hose is placed in the water to extract the sludge. There is a ring used for connecting the ropes on the bottom valve, and two ropes are fastened and fixed on both sides of the drainage ditch, so that workers on both sides can pull the ropes to move the pipeline and the bottom valve filter, which is convenient for dredging.

The customer reported that the underwater dredging pump was only idling and could not extract water at the beginning. the reason is that they did not know how to irrigate the underwater dredging pump and how to start it. The correct operation is as followed. First, close the gate valve of the outlet pipe (the pump cannot be filled and started without the gate valve). Secondly, ensure that the suction pipe and the bottom valve do not leak water (not air leakage). Third, make sure that the suction pipe goes straight down at the suction port (it cannot be bent seriously in the middle). In this way, when filling the underwater dredging pump, the suction pipe can be full filled with water and hasn’t air in it. Start the underwater dredging pump after the pump cavity is completely filled with water, and open the outlet gate valve slowly for dredging after the underwater slurry pump running smoothly.

The customer operated the dredging pump followed the above procedure. The underwater dredging pump still could not discharge water. After on-site investigation, the OCEAN PUMP engineers found that the actual working conditions were inconsistent with the original design conditions. The water depth was only about 0.2 meters. The bottom was not silt, but some hardened sand, which was more than 1 meter deep and had poor fluidity, people could stand on it. The underwater dredging pump can not pump the hardened sand if only be equipped with bottom valve filter. In this small puddle with a diameter of less than one meter, as soon as the underwater dredging pump is started, the water is extracted. Not enough water supplying causes the phenomenon of air suction.

Underwater Dredging Pump is Used for dredging in River, Wharf and Flood Ditch
Underwater Dredge Pump is Used for dredging in River, Wharf and Flood Ditch
Submersible Dredging Pump is Used for dredging in River, Wharf and Flood Ditch

Final Solution

A. Artificially make slurry. Use high-pressure water from the high-pressure water gun to impact and stir the deposited sediment layer.

B. Increase water supply.

C. Close the outlet gate valve a little to reduce the water discharge volume.

D. Place the underwater dredging pump on the shore at the beginning, put the bottom valve filter into the puddle to extract sand. After completing the partial cleaning at the bottom of the ditch, place the underwater dredging pump in the cleaned area to work.

The underwater dredging pump is connected with a 15-meter-long suction hose, its suction diameter can reach 30 meters. The dredging work can be finished by moving the submersible dredging pump about 15 times in this 400-meter ditch. Compared to previous installations, this installation requires a crane to move the underwater dredging pump every time. The advantage of this kind of installation is as follows.

A. Most of the centrifugal underwater dredging pump is submerged in water, so it can be started directly without irrigation.

B. The filter screen can be moved by being lifted out of the water surface. Similarly, the filter screen can be directly lifted out for cleaning if it is blocked. Since the centrifugal underwater dredging pump can run idly, there is no need to stop the pump. After cleaning the filter screen, put it into water, the submersible slurry pump can resume normal operation, and there is no need to stop and fill the pump with water, which saves a lot of time and improves work efficiency.

The user finally successfully completed the flood discharge ditch dredging project.

The Shanghai Waterway Bureau encountered such a problem during the working in the deep-water wharf. The sediment on the seabed a little far from the wharf can be dug up by a large dredger to clear the channel. But around the wharf where the dredger can not access, the sediment is difficult to be cleaned. The water depth of the wharf is 10-20 meters, which is difficult for the slurry pump on the ship to carry out the dredging work. The problem can be solved by using a underwater dredging pump equipped with auxiliary equipment and a hydraulic mixer, because it can dive to a very deep seabed.

When the underwater dredging pump works in deep water (20-40 meters) in the river and the sea, in addition to the problem of the motor submerged depth(which can be solved by various measures such as air pressure balance, air seal, and balanced mechanical seal), there are also pulping problem. This process of stirring the solid sedimentary sand to form a relatively uniform mud slurry is called slurry making. The pulping problem here is manifested in the fluctuating concentration of the discharged sand, and the average concentration is low. The pulping problem has been encountered in many sand mining and dredging projects, but the water in general projects is not deep, and the ground pulping is relatively easy, which can be directly controlled by humans. But it is not easy to solve in deep water, so OCEAN PUMP also put a lot of energy into research.

Submersible Mud Pump is Used for dredging in River, Wharf and Flood Ditch
Submersible Slurry Pump is Used for dredging in River, Wharf and Flood Ditch
Submersible Sand Pump is Used for dredging in River, Wharf and Flood Ditch

A. The ultra-large flow centrifugal underwater dredging pump does not require to make slurry, its super large flow creates a huge suction force at the suction port, which can quickly suck up the nearby sediment. For example, the suction port diameter of the sand pump used on the South Korean sand suction ship is about 1 meter, and the flow rate reaches 3000m3/h. It takes about 1 to 2 hours to pump such a ship of sand.

The maximum negative pressure at the sand pump suction port is theoretically equal to 1 atmosphere, 1 standard atmosphere = 100kPa = 101325 N/㎡.

The maximum suction force of the water suction port with a diameter of 1 meter is 8116 KGF, which means that the maximum suction force can be 8 tons, and even large stones can be extracted. In addition, the large flow sand pump can generate a large vortex near the suction port when working, which improves the sand suction effect.

The maximum suction force of the suction port with a diameter of 0.3 meters is 720kg, and the matching sand pump flow rate is about 300m³/h.

The maximum suction force of the suction port with a diameter of 0.25 meters is 500kg, and the matching sand pump flow rate is about 200m³/h.

The suction port with a diameter of 0.125 meters has a maximum suction force of 125kg, and the matching sand pump flow rate is about 50m³/h.

It shows that the larger the flow rate, the better the sand suction effect. But such a large flow requires a super-power motor. For example: flow rate 3000m³/h, lift 30 meters, ZJQ3000-30 centrifugal underwater dredging pump needs to be equipped with 710kW 6000V high voltage motor. This requires high-power generator sets and corresponding pipelines, valves, hoisting and other facilities. For general sand pumping and dredging projects, the cost is too high, the equipment is too large and heavy, and the operation is not very convenient.

B. Some small underwater mud pumps used for cleaning pools are equipped with a stirring impeller instead of high pressure water gun. It can generate axial water flow during working, stir up a small amount of sludge at the bottom of the pool, then the underwater mud pump discharge it. Now some of the submersible sand pumps are also installed with stirred impellers, under certain working conditions, it can reduce pump blockage by improving the liquid flow form at the impeller water suction port or cleaning the mud and sand on the filter. However, it is unrealistic to stir the sediment in the water by the axial water flow produced by such a small impeller. Moreover, the exposed impeller are easily blocked by the stone, thereby splashing the stones and sands, the pump is easily damaged, and there is also a safety hazard.

C. External mechanical stirring facilities are commonly seen in the high concentration slurry making such as slurry conveying.

Underwater Sand Pump is Used for dredging in River, Wharf and Flood Ditch
Underwater Slurry Pump is Used for dredging in River, Wharf and Flood Ditch
Underwater Mud Pump is Used for dredging in River, Wharf and Flood Ditch

According to foreign documents, the Shanghai Waterway Bureau designed hydraulic reamer-assisted mixing systems and do experiments in different working conditions by using OCEAN PUMP ZJQ28-35 centrifugal submersible mud pump and ZJQ220-22 30KW underwater dredging pump. The actual sand dredging effect is affected by many factors such as the quantity of reamers, the distance and height difference between the reamers and water suction filter, the sand pump flow rate, the working conditions on site. The actual operation should be continuously adjusted, otherwise, the sand dredging effect would be affected. The usage is complicated and the cost is too high.

The deposited sand in Liujiaxia Reservoir is relatively hard, and the sand pump cannot extract medium, so adopting the method of piling. The pile with holes is hit into the sand then pulled up, repeating the process. The harden sand layer is dispersed by the hammer vibration and water pump injection. Then close the valve of the water pump and start the underwater dredging pump for sand extracting.

D. Hydraulic stirring for slurry making. This is the most common process in all sand dredging projects. When working on the beach, riverside and in tail sand pond, the underwater dredging pump is usually hung into the puddle with a tripod, then the high pressure water gun rushes the sand into the puddle to form sand slurry which is pumped by underwater dredging pump. When working underwater, due to difficult operation, the water suction filter is usually equipped with water flushing device. Compared with no flushing device, the sand suction effect is improved, especially for loose silt. If the sediment hardens badly, the sand suction effect will not change too much.

In the seabed sand dredging project of Equatorial Guinea, Tianjin first navigation bureau has the 75kw and 50kw generators on the dredger. They use OCEAN PUMP ZJQ220-30 45KW centrifugal submersible mud pump and ZJQ140-30 30kw underwater dredging pump at the depth of underwater 20 ~ 30m. The underwater dredging pump is equipped with air pressure balancing device to balance the pressure difference inside and outside the motor chamber by injecting compressed air into the motor chamber, so the underwater dredging pump can work properly at 30 meters under water. In addition, in order to increase the sand suction concentration, water spraying and sand flushing equipment is installed at the bottom of the underwater dredging pump. The large filter screen with a diameter of 1m covered the sand pump body can effectively prevent the sand pump from being buried by the collapsed sediment, which is equivalent to adding an integral hydraulic mixer. The actual use effect is very good. Tianjin first navigation bureau has purchased this product for several years and tendered with the same model underwater dredging pump in the project of sand pumping and island filling in the South China Sea.

Tai’an Ocean Pump Co., Ltd. (referred to as OCEAN PUMP) is a professional manufacturer, supplier and exporter of sand pump machine such as sand pump, slag pump, mud pump, slurry pump, dredging pump, gravel pump, submersible slurry pump and sand dredger. OCEAN PUMP integrates independent research and development, equipment manufacturing, and pre-sales service. The company’s business covers the sand dredging project, the products cover more than 500 specifications of 20 series and are exported to 36 countries and regions. OCEAN PUMP has won praise and trust in our customers with more than 20 years industry experience, professional technology, and excellent service. Please feel free to contact us if you have any question in sand dredging equipment.