Installation principle and maintenance of multi-stage pumps

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Multi-stage pumps can be used in industrial and municipal water supply and drainage systems, for boosting water pressure at high heights, in garden irrigation, for circulating hot and cold water under increased pressure, and as part of various equipment. They can be classified into single-stage centrifugal pumps, multi-stage centrifugal pumps, pipeline centrifugal pumps, chemical process centrifugal pumps, fluoroplastic centrifugal pumps, corrosion-resistant centrifugal pumps, and so on. The working principle of a multi-stage pump is as follows: when the motor driving the pump rotates the impeller on its shaft at high speed, the liquid contained within the impeller is forced, by centrifugal force, to move from the center of the impeller along the flow channels between the blades toward the periphery of the impeller. Due to the action of the blades, both the pressure and velocity of the liquid increase. The liquid then flows through the flow channels in the casing toward the next stage of impellers, and in this way, it passes through all the impellers and casings successively, further increasing the pressure energy of the liquid. By stacking each impeller one after another, a certain head is achieved. Multi-stage pumps are a type of centrifugal pump; they also rely on the rotation of impellers to generate centrifugal force, thereby moving the fluid. The gas density is reduced until it falls within the operating range of the mechanical vacuum pump, thereby gradually achieving a high vacuum. An appropriate amount of water is installed in the multi-stage pump body as the working fluid. As the impeller rotates in a clockwise direction, water is thrown outward by the impeller; due to centrifugal force, the water forms a closed ring of approximately uniform thickness, shaped according to the geometry of the pump chamber. The inner surface of the lower part of the water ring is in perfect tangency with the impeller hub, while the inner surface of the upper part of the water ring is in contact with the tips of the blades (in fact, the blades extend to a certain depth within the water ring). At this point, a crescent-shaped space is formed between the impeller hub and the water ring, and this space is divided by the impeller into several small chambers, one for each blade. Starting from 0° at the lower part of the impeller, as it rotates through 180°, the volume of these small chambers increases, and they become connected to the suction inlet on the end face; at this time, gas is drawn in. Once suction is complete, the small chambers are separated from the suction inlet ； As the impeller continues to rotate, the small cavity becomes smaller, causing the gas to be compressed ； When the small chamber is connected to the exhaust port, the gas is expelled from the pump. Criteria for selecting multi-stage pumps: When designing equipment, the design team must determine the purpose and performance parameters of the multi-stage pump and select the appropriate type of pump. This selection process begins with choosing the type and design of the pump. The principles guiding the selection of multi-stage pumps are such that the chosen model and its performance meet the requirements related to flow rate, head, pressure, temperature, net positive suction head, suction lift, and other process parameters of the system. Multi-stage pumps must also meet the requirements imposed by the properties of the medium being transported. For pumps used to transport flammable, explosive, toxic, or valuable substances, it is necessary to have reliable shaft seals or to use leak-free pumps, such as magnetically driven pumps (which have no shaft seals and rely on indirect magnetic drive). For multi-stage pumps used to handle corrosive media, the components involved in the flow process need to be made of corrosion-resistant materials, such as those used in fluoroplastic corrosion-resistant pumps. For pumps transporting media containing solid particles, the components involved in the flow process should be made of wear-resistant materials; when necessary, the shaft seals should be flushed with a clean liquid. Mechanically, multi-stage pumps are required to have high reliability, low noise, and minimal vibration. Correctly calculate the total cost of purchasing multi-stage pumps, including the purchase cost as well as the installation and maintenance costs. Installation instructions for multi-stage pumps: 1. During installation, the weight of the pipelines should not be borne by the pump, as this can easily damage the pump. 2. The pump and motor form an integrated unit that has been calibrated by the manufacturer before leaving the factory; therefore, no adjustments are required during installation, making it very convenient. 3. Before installing the pump, carefully check the pump’s flow channels for any hard objects that could interfere with its operation (such as stones or iron particles), to prevent damage to the internal components while the pump is in use. 4. The foundation bolts must be tightened firmly, and the pump should be checked at regular intervals to ensure they remain tight. This prevents severe vibrations when the pump starts, which could affect its performance. 5. For easier maintenance and safer operation, install a control valve on the pump’s inlet and outlet pipelines, as well as a pressure gauge near these connections. For pumps with high head pressures, a check valve should also be installed in front of the outlet valve to prevent water hammer effects in case of power outages, thereby ensuring the pump operates under optimal conditions and extending its lifespan. 6. When the pump is used in applications that require lifting capacity, a bottom valve should be installed. Additionally, the inlet pipeline should have as few bends as possible, and there should be no leaks of water or air, as these factors can affect the pump’s suction ability. 7. To prevent impurities from entering the pump and blocking the flow channels, a filter should be installed in front of the pump’s inlet. 8. Before installing the pipelines, rotate the pump’s rotor components to ensure there are no signs of friction or sticking. If such issues exist, the pump needs to be disassembled to identify the cause. For the repair of multi-stage pump failures, the bearing housings and the main cover were removed; it was found that the shaft sleeves and the ring seals at the inlet of the rotor blades were severely worn. The clearance at the inlet of the rotor blades in each stage had reached as much as 1.5 mm, which is well above the acceptable limit. The shaft’s runout was within the specified limits, indicating that the shaft was not bent. After reseating the worn mouth rings (with the thickness of the seating set such that the total gap between the inner and outer mouth rings was 0.5 mm), the impeller was installed, and the rotor was balanced dynamically. Following alignment work on the coupling, a trial operation period of over one month showed that the vibration levels of the unit were good and stable; the vibration values of the pump dropped to normal levels, and the peak energy values indicating the vibration condition of the bearings remained stable throughout.