Comprehensive introduction to the basics of slurry pumps

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Concept and Types of Slurry Pumps 　　　Slurry pumps, from a physical principles perspective, belong to the category of centrifugal pumps. Conceptually, they are machines that utilize the centrifugal force generated by the rotation of the pump impeller to increase the energy of solid-liquid mixtures; they are devices that convert electrical energy into kinetic and potential energy of the medium. 　　 　　A slurry pump is a type of centrifugal pump classified based on the medium it transports. Additionally, slurry pumps can be classified into different types from various perspectives: 1. Based on the number of impellers: single-stage pumps and multi-stage pumps. 2. Based on the position of the pump shaft relative to the horizontal plane: horizontal pumps and vertical pumps (submersible pumps). 3. Based on the way in which water is drawn in by the impeller: single-suction pumps and double-suction pumps. 4. Based on the structure of the pump casing: horizontally split type and vertically integrated type.

Uses of slurry pumps
Slurry pumps are widely used in industries such as mining, power generation, metallurgy, coal processing, and environmental protection for transporting slurries containing abrasive solid particles. Such as slurry transportation in metallurgical concentrators, hydraulic ash removal in thermal power plants, coal slurry and heavy medium transportation in coal washing plants, river dredging, and river desilting. In the chemical industry, it can also transport some corrosive slurries containing crystals. 　　 　　Currently, about 80% of the applications for slurry pumps are in mineral processing plants within the mining industry. Due to the harsh conditions in the primary ore processing stage, the service life of slurry pumps in this section is generally low. Of course, different ores have varying degrees of abrasiveness. 　　 　　In the coal washing industry, due to varying operating conditions, larger coal lumps and coal gangue can easily cause blockages, which imposes high demands on the design of slurry pumps. A coal washing plant under the Huaibei Mining Bureau adopted specially designed slurry pumps in 2005 to replace those originally imported from Australia; they have been operating properly ever since, capable of transporting large coal lumps and coal gangue without any blockages, and their service life exceeds that of the imported pumps. 　　 　　In the field of seawater sand selection, the use of slurry pumps is also gradually gaining recognition from customers. However, when selecting sand from seawater or digging for sand in rivers, slurry pumps are more commonly referred to as sand pumps or dredge pumps. Although they go by different names, in terms of their structural characteristics and operating principles, they can all be generally referred to as slurry pumps. Therefore, in seawater sand selection, we often refer to it as a sand pump; in river dredging, it is conventionally called a dredge pump. 　　 　　Although slurry pumps have a wide range of applications, proper use is very important. Due to the limitations inherent in their names, slurry pumps are often misunderstood by those outside the industry. In reality, mud pumps, slurry pumps, dredge pumps, and silt-clearing pumps all fall under the category of pumps used for handling impurities. In the application of slurry pumps, it is essential to pay attention to proper design, accurate calculations, and appropriate selection – these aspects are very important. 　　 　　Structural description of slurry pumps 　　　Pump head section 　　　1. The ZJ, ZG, ZH, ZM, and ZHH types of slurry pumps feature a dual-casing structure; that is, the pump body and pump cover are equipped with replaceable wear-resistant metal linings (including the impeller, shroud, guards, etc.). The pump body and pump cover are manufactured from gray cast iron or ductile iron depending on the operating pressure; they are vertically split and connected by bolts. The pump body has locating tabs that are bolted to the bracket. The discharge direction of the pump can be rotated and installed at eight angles. The front and rear cover plates of the impeller are equipped with back blades to reduce leakage and extend the pump’s service life. 　　 　　2. ZH Slurry Pump This series of pumps are horizontal, vertically centered, double-casing slurry pumps. The pump body and cover are equipped with replaceable metal linings made of high-chromium wear-resistant alloy; these linings can be used until they are worn out, thereby extending the maintenance interval and reducing operating costs. The outlet direction of the pump can be rotated and installed at 8 different angles. 　　 　　Bearing assembly: The pump’s bearing assembly features a cylindrical design, which facilitates the adjustment of the gap between the impeller and the front shield; it can be removed as a whole for maintenance. The bearings are lubricated with grease. 　　 　　Shaft seal (sealing): The shaft seal types for pumps include packing seal, impeller seal, and mechanical seal. 　　 　　Transmission methods: V-belt and triangular belt transmission, elastic coupling transmission, gear reduction box transmission, hydraulic coupler transmission, variable frequency drive units, thyristor speed control, etc. Among them, the V-belt drives include CR, CL, CV, ZV, ZL, and ZR drives. 　　 　　Overall performance: The pump features a wide performance range, good cavitation resistance, and high efficiency. A multi-stage series technology can be employed to meet long-distance transmission requirements. There are various metals available for the overcurrent components, and the depth can be increased. Multiple speeds and various variations are employed to ensure the pump operates under optimal conditions in industrial and mining applications. It has a long service life and high operational efficiency, and can meet various harsh conveying conditions. 　　 　　3. The ZD and ZS(H) types have a single-pump structure (i.e., without an inner lining). The pump body, pump cover, and impeller are made of wear-resistant metal. The connection between the pump body and the pump cover features a special clamping mechanism; the pump outlet can be rotated freely, making installation and removal convenient. 　　 　　4. The ZL type slurry pump is a vertical slurry pump, with the pump body, pump cover, and shaft arranged vertically perpendicular to each other. The ZL type is also a single-shell pump, with the pump body and cover available in metal or rubber. 　　 　　5. The professional terms for the pump head of a slurry pump are the pump body and the pump cover. The so-called pump head of a conventional slurry pump should consist of the pump body and the pump cover. The pump body is primarily connected to the pump’s rotor; bearings are used to link the impeller, the seals, and the bearing assembly together. The pump cover is the part that corresponds to the pump body, and together with it they form a sealed chamber. Inside the pump body and pump cover is the liner of the slurry pump. The materials for the lining are generally rubber and high-chromium alloy; the choice between a rubber lining or a metal alloy for the pump is usually determined based on the working conditions in industrial or mining settings. 　　 　　6. The inlets of all types of pumps are horizontal, and when viewed from the drive direction, the pumps rotate clockwise. 　　 　　Precautions for operating slurry pumps 　　　When a slurry pump is in operation, it must be placed on solid ground, with the suction pipe submerged in water; moreover, the pump needs to be primed before it can start working. Due to structural constraints, mud pumps and submersible slurry pumps require the motor to be placed above the water surface while the pump itself is submerged in water; therefore, it must be secured, otherwise the motor falling into the water will result in its destruction. Moreover, since the length of the long axis is generally fixed, the pump is difficult to install and use, which limits its applications significantly. 　　 　　If there are standby pumps, it’s best to use the two pumps alternately. If the pump gets clogged, the only option is to repair it. A mesh screen can be installed at the water inlet to prevent excessive debris from entering the pump, which will significantly reduce the likelihood of clogging. 　　 　　Pumps can be divided into electrical and mechanical aspects; regarding the mechanical aspect, it is sufficient to retrieve the previous maintenance records for comparison. Next is the electrical aspect; it is necessary to know the power of each pump motor and to have a certain understanding of its control system. For slurry pumps equipped with mechanical seals, it is necessary to ensure the supply of shaft seal water. Operation without water is strictly prohibited, otherwise the mechanical seal will be damaged. 　　 　　Selection and design of slurry pumps The selection and design of slurry pumps have a significant impact on their service life and operational stability. A scientifically sound selection and design will determine whether your slurry pump can achieve optimal, efficient operation. 　　 　　Efficiently operating slurry pumps have three main characteristics: First, they operate with high efficiency and minimal losses. 　　 　　Second, the flow-through components of the pump have a relatively long service life, which helps to reduce production costs. 　　 　　Third, the entire industrial and mining system operates stably, and issues with pump operation do not affect its functioning. 　　 　　Therefore, before commissioning the system, users must choose a company with the necessary capabilities and expertise to carry out the selection and design of the slurry pumps. This will bring you significant overall benefits. To evaluate a slurry pump manufacturer’s capability in product selection, the following factors can be considered: First, the company should have the latest and most scientifically sound selection manuals. Generally, when a slurry pump manufacturer designs models for customers to choose from, they refer to selection manuals. The scientific validity of the data in this manual completely determines whether the selected pump type is appropriate. 　　 　　Second, experienced engineers. An experienced selection engineer with many years of experience is very important, as engineers who have spent years working on industrial and mining design projects and involved in product selection possess extensive practical experience. They are well-versed in customers’ requirements, as well as in the conditions in industrial and mining environments and the operation of pumps. Therefore, their selection and design will be very scientific and reasonable. 　　 　　Third is the company’s overall design capability. This might not seem directly related to the selection process, but if the company you choose lacks sufficient design capabilities, it will also affect the quality of your pump selection. Since industrial and mining operations can be considered as a single system – not just a matter of pumps, but the entire system as a whole – many devices operate within this system; therefore, when selecting the model of slurry pump, the company must have the capability for overall system design. 　　 　　Daily maintenance of slurry pumps: 1) The water pressure and flow rate for the bearings must meet the specified requirements; adjust (or replace) the tightness of the packing as needed to prevent leakage at the shaft seal. And replace the shaft sleeve in a timely manner. 　　 　　2) When replacing the bearings, it is essential to ensure that there is no dust inside the bearing assembly and that the lubricating oil is clean. During operation, the temperature of the bearings should generally not exceed 60–65°C, with a maximum of 75°C. 　　 　　3) It is necessary to ensure the coaxiality between the motor and the pump, as well as to ensure that the elastic pads in the coupling are intact and in good condition; they should be replaced promptly if damaged. 　　 　　4) Ensure that the pump components and piping system are installed correctly, firmly, and reliably. 5) Some parts of the slurry pump are vulnerable components; it is necessary to pay attention to their wear during regular use, and repair or replace them promptly. During the repair or replacement of the vulnerable parts of a slurry pump, it is necessary to ensure proper assembly and appropriate adjustment of gaps, in order to avoid tight friction. 　　 　　6) The suction piping system of the slurry pump must be leak-free; during operation, attention should also be paid to whether there is any blockage at the suction inlet. The media to be handled by slurry pumps often contain solid particles; therefore, the grates placed in the pump intake sump must meet the requirements regarding the size of particles that the slurry pump can handle, thereby reducing the likelihood of blockages caused by overly large particles or long fibrous materials entering the pump. 　　 　　Sealing of slurry pumps 　　　There are advantages and disadvantages associated with each of the three sealing methods: 　　　1. Packing seal – this is the most common type of seal. It works by injecting shaft seal water under pressure into the packing, thereby preventing the leakage of slurry from the pump. Packing seals are used in multi-stage series pumps where shaft seals using impellers are not suitable. The stuffing box seal has a simple structure, is easy to maintain, and is inexpensive. 　　 　　2. The impeller seal prevents the slurry from leaking out by utilizing the force of an impeller that generates countercentrifugal force. For single-stage pumps or the first stage of multi-stage series pumps, where the positive pressure at the pump inlet is no more than 10% of the pressure at the pump outlet, an auxiliary impeller shaft seal can be used. This type of seal has advantages such as the need for no seal water, no dilution of the slurry, and excellent sealing performance. Therefore, this type of sealing can be considered when dilution in the slurry is not allowed. 　　 　　3. Mechanical seals are generally used in situations where high sealing requirements exist. Especially in the chemical and food industries, not only is sealing required, but it is also crucial that no additional substances be allowed to enter the pump. The disadvantages are high costs and difficulty in maintenance, etc.