What is the difference between a submersible dredge pump and a submersible sewage pump?

Why do many manufacturers recommend submersible dredge pumps as submersible sewage pumps to customers? Many customers who use submersible dredge pumps can’t tell the difference between the two pump. How can there be many differences? Why are prices so different? This is also because there is no unified national standard for submersible dredge pumps, which also gives some manufacturers the opportunity to confuse the concept of submersible dredge pumps, and recommends the lower price submersible sewage pumps to customers at a higher price.

submersible dredge pump
submersible dredge pump

Let’s discusses the difference between submersible dredge pumps and submersible sewage pumps.

  1. Concept difference between submersible dredge pump and submersible sewage pump
  2. The submersible dredge pump is used to remove the sediment or slurry in the working condition. Submersible sewage pump is a water pump used to drain water or sewage.
  3. Different from the design and working conditions.

Submersible sewage pump is designed by the principle of one-phase flow, and submersible dredge pump is to improve the efficiency of pumps in pumping sand slurry or mud.

However, when some manufacturers recommend products to customers, they often sell submersible sewage pumps as submersible dredge pumps. It is difficult for users to distinguish from appearance and performance parameters.

The fundamental basis for distinguishing between submersible dredge pumps and submersible sewage pumps should be the product industry standard.

However, since there is no industry standard for submersible dredge pumps.This has caused a chaos in the market for submersible dredge pumps. Many manufacturers sell low-cost submersible sewage pumps as high-cost submersible dredge pumps.

  1. The components of the sand in the slurry are different, and the slurry concentration is different. The service life of the submersible dredge pump varies greatly. Check the product standard, the submersible dredge pump and submersible sewage pump has different drainage conditions:

Submersible sewage pumps are designed for pumping domestic wastewater (sewage). Working conditions require that 4% non-abrasive solids are allowed in the water.

The submersible dredge pump is designed for pumping water rich in sediment. The standard stipulates that it is suitable for conveying liquid containing suspended solid particles (such as quartz sand, ore, rock, ash, coal, gravel, etc.). The maximum allowable value of the slurry density of the transmission medium is divided into three grades, namely:

  1. Low-concentration working condition, density ≤1100kg/m3, main use place: used in coal mining area, conveying coal slime and crushed coal particles. Maximum allowable concentration (severity ratio): fine coal slime content 29%, tail coal slime content 20%, quartz sand content 15%, and tailings sand 13%.
  2. High-concentration working condition, density ≤1300kg/m3, the main place of use: technological process slurry transportation, or rock blasting construction drainage without specific measures to control sediment content. The maximum allowable concentration (severity ratio): fine coal slime, tailings slime content 40%, quartz sand content 37%, tailings sand 33%.
  3. Ultra-high concentration working conditions, density ≤1500kg/m3, the main places of use: professional sand mining, transportation of tailings sand, or thick slurry transportation without specific measures to control sediment content. The maximum allowable concentration (severe ratio): 60% of fine slime and tailings slime, 40% of yellow clay, 54% of quartz sand, 48% of tailings sand and 42% of iron concentrate.
submersible dredge pumps
submersible dredge pumps

Second, the choice of matching motor

Pump output power P = ρgQH, where ρ-the density of the pump transport slurry, g-gravity acceleration, Q-pump flow rate, H-pump head.

The submersible sewage pump is designed according to the water density 1000kg/m3. The density of the mortar will be much higher than the water density. If the submersible sewage pump is used as a submersible dredge pump for pumping sand, the motor load is too large and it is easy to burn the motor. At this time, some manufacturers will use the method of reducing the diameter of their impeller to reduce the actual parameters of the pump type and avoid burning the motor.

The theoretically calculated output power of the pump is much smaller than the actual output power. The power of the submersible dredge pump is not only as simple as multiplying the power of the clean water pump motor with the slurry density, but also increases the safety by 1.3 to 2 times. margin. This is because the size of the slurry concentration is difficult to control when the sand pump is working, and the density of the transported slurry suddenly increases and decreases, causing the output power of the sand pump to change accordingly. In addition, when the sand pump is started and operated, the solid particles will impede the rotation of the impeller (the impeller will be caught in severe cases), which will further increase the output power of the sand pump. The larger the solid particles in the slurry, the greater the uncertainty. Therefore, when designing and matching the motor power of the sand pump, not only the rated output power of the water pump but also the maximum output power must be considered.

Submersible dredge pumps are generally equipped with four-stage or six-stage low-speed, high-torque motors, and submersible sewage pumps are generally equipped with two-stage motors with a speed of 2980 rpm. The high-speed motor has a high speed, so if the parameters are the same flow rate and head, the volume of the pump casing and impeller is small, but the higher the speed, the faster the wear rate, which causes the pump casing and impeller to wear when the submersible sewage pump is pumping sand soon, it is necessary to shut down frequently to replace accessories, and the maintenance cost is high.

  1. The structural characteristics of submersible dredge pump and submersible sewage pump are different.

When the water contains sediment, the main phenomena of pump damage are burning motor and impeller wear. The vast majority of them are burning the motor, the main reason is that the motor is overloaded or the motor enters the water. Motor overload can be solved by increasing the power of the supporting motor, or by increasing the cooling water circulation. The water intake of the motor is mainly a sealing problem, especially how to ensure that the mortar is completely isolated from the motor when pumping sand, and to avoid the water source containing the mortar from entering the motor. It has been a problem that needs to be solved in the manufacture of submersible sand pumps.

To extend the service life of submersible dredge pumps, the problems of sand pumping seal and sand pumping wear must be solved. The main problem here is the sand pumping seal problem. Tai’an PCEAN Pump Industry Co., Ltd. adopts a specially designed double-face cemented carbide mechanical seal to improve the reliability of the mechanical seal. The machine seal is lubricated with oil, and there is a large amount of engine oil in the machine seal cavity, which can further prevent the entry of the mortar liquid.

Furthermore, there is a separate oil chamber between the machine seal and the motor, which is the channel connecting the motor and the impeller. Even if the machine seal fails, a small amount of leaked slurry will flow to the machine oil chamber and will not contact the motor or the bearing, avoiding bearing grease Loss can extend bearing life.

submersible dredge pumps
submersible dredge pumps

Fourth, the difference between submersible dredge pump and submersible sewage pump material

The submersible dredge pump casing, impeller, guard plate and other flow parts are made of wear-resistant high chromium (CR26) alloy material, after two heat treatments, Rockwell hardness is 55-60, has good wear resistance, Toughness and long service life. Submersible sewage pumps are usually made of cast iron or alloy steel with a low proportion of alloys. The wear resistance is lower than that of high chromium alloys and the pumping life is short.

Compared with the submersible sewage pump, the thickness of the impeller of the submersible dredge pump and the vulnerable parts of the pump body is much greater than that of the submersible sewage pump, which increases the anti-wear performance.

Through the above analysis, we can judge that submersible dredge pumps are completely different products from submersible pumps and submersible sewage pumps. Customers must distinguish and compare the pump type description provided by the manufacturing company, and select qualified and suitable products according to your requirements.