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Regarding some questions about screw pumps, Anhui Shengshi Datang would like to share some insights with everyone.   Causes and Hazards Analysis of Rod String Reverse Rotation in Screw Pump Wells 1. Analysis of Causes for Rod String Reverse Rotation in Screw Pump Wells During oilfield extraction using Screw Pumps, reverse rotation of the rod string is a relatively common failure. The causes of this reverse rotation are complex, but the primary reason is the sudden shutdown or sticking of the pump during operation, which causes deformation and torsion of the rod string. The rapid release of this deformation and torsion then leads to reverse rotation. Specifically, if the Screw Pump suddenly stops or sticks during operation, a pressure difference arises between the high-pressure liquid retained in the production tubing and the wellbore hydrostatic pressure in the casing annulus. Driven by this pressure difference, the Screw Pump acts as a hydraulic motor, driving the rotor and the connected rod string to rotate rapidly in reverse. The reverse rotation of the Screw Pump rod string is influenced by the tubing-casing pressure difference, exhibiting variations in reverse rotation duration and speed. Generally, a larger tubing-casing pressure difference results in faster reverse rotation speed and longer duration for the rod string. As the pressure difference gradually decreases, the reverse rotation speed and duration correspondingly decrease until the pressure difference balances, at which point the reverse rotation gradually ceases. When reverse rotation occurs, the rod string vibrates intensely. If resonance occurs during this vibration—meaning the vibration frequency of the reversing rod string synchronizes with the natural frequency of the wellhead—the rotation speed can instantly surge to its maximum. This situation can trigger serious safety accidents, cause significant harm to the worksite, and even result in casualties. 2. Hazards of Rod String Reverse Rotation in Screw Pump Wells The hazards caused by rod string reverse rotation vary in degree depending on the speed and duration of the reversal. Severe cases can lead to onsite safety incidents with serious consequences. Specifically, the hazards mainly manifest in the following three aspects: (1) Reverse rotation can cause the rod string to become displaced from its original position, leading to the swinging of the Screw Pump polish rod. This can cause significant wear and tear on the Screw Pump equipment, damaging various components and parts. (2) During reverse rotation, if the speed is too high or the duration too long, the temperature of the reversing components can continuously rise, potentially igniting flammable gases at the wellhead. This could trigger an explosion at the worksite, leading to unforeseeable serious consequences. (3) If reverse rotation is not effectively controlled, it can cause the drive pulley to shatter. Fragments of the pulley flying around the worksite pose a risk of injury to personnel, damage the oilfield production site, reduce extraction efficiency, and increase the probability of various safety incidents.   Commonly Used Anti-Reverse Rotation Devices for Screw Pump Well Rod Strings 1. Ratchet and Pawl Type Anti-Reverse Device This type of device prevents reverse rotation by utilizing the one-way engagement of a ratchet and pawl. Specifically, the ratchet and pawl engage via an external meshing configuration. When the Screw Pump drive operates normally, centrifugal force causes the pawl to disengage from the ratchet brake band, so the anti-reverse device remains inactive. However, when the Screw Pump suddenly stops during operation, the rod string begins to reverse due to inertia. During this reverse rotation, gravity and spring force cause the pawl to engage with the ratchet brake band, activating the anti-reverse device. The device then dissipates the torque generated by the high-speed reverse rotation through frictional force. The ratchet and pawl device has a simple structure, is easy to install, has a low overall cost, and offers good flexibility and controllability. However, it typically requires manual intervention at close range for activation/operation. Improper operation can cause the friction surfaces to slip, presenting a safety risk. Additionally, this type of device can generate significant noise during operation and subjects the components to considerable impact and wear, necessitating frequent part replacements. 2. Friction Type Anti-Reverse Device The friction type anti-reverse device consists of two main parts: an overrunning clutch that identifies rotation direction and a brake shoe assembly. In this device, the brake shoes are connected to the brake bodies via riveting, and the two brake bodies grip the outer ring. During normal Screw Pump operation (clockwise rotation), the device remains inactive. When a sudden shutdown causes reverse rotation, the drive mechanism reverses. In this state, rollers move between the star wheel and the outer ring, activating the device. The resulting damping effect restricts the rotation of the star wheel, thereby achieving the anti-reverse function. However, since the operation of this device often requires manual control, improper handling can lead to failure. Furthermore, replacing this device involves significant safety risks. Consequently, its application in Screw Pump wells is currently relatively limited. 3. Sprag Type Anti-Reverse Device The sprag type anti-reverse device operates based on the principle of an overrunning clutch. Specifically, during normal Screw Pump operation (forward rod string rotation), the sprags inside the device align normally and remain disengaged from the outer ring, keeping the device inactive. When the pump suddenly stops and the rod string starts to reverse rotate, the resulting reverse torque causes the device to rotate in the opposite direction. This makes the sprags align in the reverse direction, locking them against the outer ring and preventing reverse rotation of the rod string. The sprag type device has a simple construction, is easy to install, offers good controllability, and operates with high safety, minimizing the risk of accidents. It also has a long service life and does not require frequent part replacements. The drawback is that it cannot fundamentally solve the reverse rotation problem. If the reverse torque exceeds the capacity the sprags can withstand, it can cause sprag failure and device malfunction. Additionally, daily maintenance of this device can be inconvenient. 4. Hydraulic Type Anti-Reverse Device The working principle of the hydraulic anti-reverse device is somewhat similar to a car's braking system. When the Screw Pump suddenly stops and the rod string is about to reverse rotate, the hydraulic motor within the device activates. Hydraulic fluid pressure drives friction pads against a brake disc, releasing a large amount of the reverse rotation potential energy, thereby dissipating the reverse rotation of the rod string. The advantages of the hydraulic type device include stable and reliable operation, high safety, no noise generation, and no hazard to onsite personnel. Maintenance, replacement, and daily upkeep are relatively convenient and safe. This type of device can more thoroughly address the reverse rotation problem, enhancing the operational safety of the Screw Pump system. The disadvantages are its high overall cost and stringent quality requirements for the hydraulic components, leading to potentially higher maintenance and replacement costs. If issues like hydraulic fluid degradation or leaks occur during operation, the device's performance can be affected, necessitating regular maintenance.   Measures to Address Rod String Reverse Rotation in Screw Pump Wells 1. Research and Application of Safer, More Reliable Anti-Reverse Devices Analysis of the causes of rod string reverse rotation indicates that the main factors are the release of stored elastic potential energy in the rod string and the effect of the tubing-casing pressure difference. If reverse rotation is not effectively controlled, especially at high speeds or for prolonged durations, it can lead to a series of severe consequences and safety incidents, posing significant risks. Therefore, technical research and application should be strengthened. Based on existing anti-reverse devices, upgrades and improvements should be made to develop and apply safer and more reliable devices. These should ensure the safe release of torque and effective elimination of the pressure difference during sudden Screw Pump shutdowns, reducing associated safety risks. The working principles, advantages, and disadvantages of common anti-reverse devices need in-depth analysis for targeted improvements. This will enhance the stability and reliability of these devices, minimize safety risks during use, and maximize the operational safety of Screw Pump equipment. 2. Application of Downhole Anti-Backflow Switches Using downhole anti-backflow switches can effectively address reverse rotation caused by hydraulic forces. The downhole anti-backflow switch consists of components like a disc, ball, push rod, shear pin, and crossover sub. Its application in the Screw Pump drive system can reduce the torque generated during sudden shutdowns, lower the reverse rotation speed, and mitigate reverse rotation caused by the tubing-casing pressure difference. By dissipating hydraulic forces, it helps control reverse rotation and also prevents rod string back-off. The anti-backflow switch has a simple structure, low cost, and is easy to install. It has been widely used in oilfield development due to its strong stability, high reliability, and broad application prospects. 3. Strengthening Surface Safety Management To effectively control reverse rotation, it is essential not only to equip Screw Pump systems with appropriate anti-reverse devices but also to enhance safety management in surface operations and implement protective measures to reduce the adverse consequences of reverse rotation. Specific measures include: ① Personnel should perform daily inspection, maintenance, and servicing of Screw Pump equipment, maintain proper equipment management records, continuously accumulate experience, and improve safety prevention capabilities. ② Implement continuous monitoring of the Screw Pump system's operation to promptly detect abnormalities. Take immediate action for fault diagnosis and troubleshooting to reduce the probability of reverse rotation occurrences. ③ Establish comprehensive emergency response plans. For sudden reverse rotation events, immediately activate the emergency plan to lower the probability of safety incidents.

In the previous blog, we discussed the common failures of pneumatic diaphragm pumps and analyzed their causes. Now, Anhui Shengshi Datang will guide you on how to troubleshoot these issues and what steps to take when encountering such situations. Troubleshooting and Handling Measures 1. Air Pump Not Working When it is found that the pneumatic diaphragm pump cannot start normally or stops immediately after starting, it should be inspected based on this symptom: (1) First, check whether the connection points of the circuit are broken. If the circuit is damaged or the connections are loose, replace the wires in the circuit or reinforce the connections promptly to restore the equipment to operation and improve the stability of the air pump. (2) If parts that frequently experience friction show significant wear or have aged and lost elasticity, consider replacing them to enhance the stability of the system operation. 2. Inlet/Outlet Pipeline Blockage If the issue with the air pump is determined to be in the inlet/outlet pipeline, and the pump cannot operate normally due to pipeline blockage, inspect and address it based on the following symptoms: Common Faults Cause Analysis Handling Measures Insufficient pressure supply or pressure increase in the diaphragm pump Improper adjustment of the pneumatic diaphragm pump pressure regulating valve or poor air quality; malfunction of the pressure regulating valve; malfunction of the pressure gauge Adjust the pressure valve to the required pressure; inspect and repair the pressure regulating valve; inspect or replace the pressure gauge Pressure drop in the diaphragm pump Insufficient oil replenishment by the oil replenishment valve; insufficient feed or leakage in the feed valve; oil leakage from the plunger seal Repair the oil replenishment valve; inspect and repair the sealing parts; refill with new oil Reduced flow rate in the diaphragm pump Pump body leakage or diaphragm damage; rupture of the inlet/outlet valve; diaphragm damage; low speed that cannot be adjusted Inspect and replace the sealing gasket or diaphragm; inspect, repair, or replace the feed valve; replace the diaphragm; inspect and repair the control device, adjust the rotation speed (1) Disassemble and clean the internal pipelines of the equipment to remove various impurities attached to the pipelines. Improve the cleanliness of the pipe walls and enhance the stability of the equipment operation. (2) Strengthen the management of medium materials to ensure that materials do not mix due to sharing. Ideally, use one device for pumping a specific material. If the same equipment must be used, clean the pipelines promptly to avoid air pump pipeline blockages and improve the stability of the air pump's working condition. 3. Severe Ball Seat Wear If ball seat wear is confirmed through inspection, troubleshoot using the following measures: (1) First, confirm whether its sealing performance can support normal equipment operation. If the ball seat wear is too severe to determine, replace the ball seat to maintain the fit between the ball seat and the ball and avoid poor sealing. (2) Since friction between the ball seat and the ball is inevitable, monitor the operating condition of the ball seat in real time during daily operations to enhance the overall stability of the equipment. 4. Severe Ball Valve Wear If ball valve wear is confirmed through inspection, and the wear is severe, troubleshoot using the following measures: (1) Replace severely damaged ball valves. If no spare ball valve is available, temporarily use a ball bearing as a substitute and replace it with a matching ball valve afterward. (2) Media with excessively high viscosity will increase the resistance of the ball, preventing flexible operation. In this case, clean the ball valve and base to ensure smooth transportation and improve the stability of the equipment operation. 5. Irregular Air Pump Operation For issues related to irregular air pump operation, inspect and address them based on the specific symptoms: (1) Replace severely worn ball valves to improve structural stability. (2) If the diaphragm is damaged, replace it promptly to enhance the reliability of the system's processing. (3) If the issue is due to limitations of the preset system, upgrade the system to improve the stability of the equipment system operation. 6. Insufficient Air Supply Pressure For problems caused by insufficient air supply pressure, inspect and troubleshoot using the following measures: (1) Confirm whether the equipment operating system is stable and check the system pressure condition. If it meets the requirements, continue using it; otherwise, debug it as soon as possible. (2) To maintain the volume and cleanliness of compressed air, add an air filtration device and improve the purity of the compressed air to maintain the equipment output rate and enhance system stability.  

Anhui Shengshi Datang Pump Industry is committed to providing customers with the best technology and services, always putting customers at the core.   Introduction to Pneumatic Diaphragm Pumps A pneumatic diaphragm pump uses compressed air as its driving power source. It typically consists of components such as an air inlet, air distribution valve, balls, ball seats, diaphragms, connecting rods, central bracket, pump inlet, and exhaust outlet. Once it receives a control command, the pump starts operating by utilizing air pressure and its special internal structure to transfer materials. It has low requirements for the properties of the conveyed medium and can handle a wide range of substances, including solid–liquid mixtures, corrosive acid and alkali liquids, volatile, flammable, and toxic fluids, as well as viscous materials. It offers high working efficiency and simple operation. However, due to aging parts or improper use, diaphragm pump failures may occur during operation. A. Materials Pneumatic diaphragm pumps are commonly made from four materials: aluminum alloy, engineering plastics, cast alloy, and stainless steel. Depending on the medium being handled, the pump materials can be adjusted accordingly to meet the diverse needs of users. Owing to its adaptability to different environments, the pump can handle materials that conventional pumps cannot, earning it wide recognition among users. B. Working Principle The diaphragm pump operates by using a power source to drive the piston, which in turn moves hydraulic oil back and forth to push the diaphragm, thereby achieving suction and discharge of liquids. When the piston moves backward, the change in air pressure causes the diaphragm to deform and concave outward, increasing the chamber volume and decreasing pressure. When the chamber pressure drops below the inlet pressure, the inlet valve opens, allowing fluid to flow into the diaphragm chamber. Once the piston reaches its limit, the chamber volume is at its maximum and the pressure is at its minimum. After the inlet valve closes, the suction process is complete, and liquid filling is achieved. As the piston moves forward, the diaphragm gradually bulges outward, decreasing the chamber volume and increasing internal pressure. When the pressure in the chamber exceeds the resistance of the outlet valve, the liquid is expelled. Once the piston reaches the external limit, the outlet valve closes under gravity and spring force, completing the discharge process. The diaphragm pump then proceeds to the next suction and discharge cycle. Through continuous reciprocation, the diaphragm pump effectively transfers the liquid. C. Characteristics 1. Low heat generation: Powered by compressed air, the exhaust process involves air expansion, which absorbs heat, reducing the operating temperature. Since no harmful gases are emitted, the air properties remain unchanged. 2. No spark generation: As it does not rely on electricity, static charges are safely discharged to the ground, preventing spark formation. 3. Can handle solid particles: Due to its positive displacement working principle, there is no backflow or clogging. 4. No impact on material properties: The pump merely transfers fluids and does not alter their structure, making it suitable for handling chemically unstable substances. 5. Controllable flow rate: By adding a throttling valve at the outlet, the flow rate can be easily adjusted. 6. Self-priming capability. 7. Safe dry running: The pump can operate without load without damage. 8. Submersible operation: It can work underwater if needed. 9. Wide range of transferable liquids: From water-like fluids to highly viscous substances. 10. Simple system and easy operation: No cables or fuses are required. 11. Compact and portable: Lightweight and easy to move. 12. Maintenance-free operation: No lubrication needed, eliminating leakage and environmental pollution. 13. Stable performance: Efficiency does not decline due to wear.   Common Failures and Causes Although pneumatic diaphragm pumps are compact and occupy little space, their internal structure is complex, with many interconnected components. Failure of any single part can lead to operational problems. Unusual noise, fluid leakage, or control valve malfunctions are typical warning signs. Timely maintenance is essential. Component wear and aging caused by friction are also major sources of malfunction. A. Pump Not Operating 1. Symptoms: When starting, the pump either does not respond or stops running shortly after starting. 2. Causes: a. Circuit issues such as disconnection or short circuit prevent proper operation. b. Severe component damage — for example, worn ball valves or damaged air valves — leads to loss of pressure and system shutdown. B. Blocked Inlet or Outlet Pipeline 1. Symptoms: Reduced working pressure, weak suction, and slow fluid transfer. 2. Causes: a. High-viscosity materials adhere to the inner pipe walls, reducing diameter and smoothness, increasing resistance. b. Use of multiple materials without thorough cleaning causes chemical reactions between residues, affecting normal operation. C. Severe Ball Seat Wear Continuous friction wears down the surface of the ball seat, creating gaps between the ball and seat. This may cause air leakage and reduced pump output. D. Severe Ball Valve Wear 1. Symptoms: Irregular ball shape, visible surface pitting, or heavy corrosion reducing ball diameter. 2. Causes: a. Manufacturing inconsistencies cause mismatch between the ball and seat. b. Long-term operation under friction and corrosive environments accelerates valve damage. E. Irregular Pump Operation 1. Symptoms: The pump fails to complete normal suction and discharge cycles even after adjustment. 2. Causes: a. Worn or damaged ball valve. b. Aged or broken diaphragm. c. Incorrect system settings. F. Insufficient Air Supply Pressure or Poor Air Quality Insufficient air pressure leads to reduced gas volume entering the air chamber, resulting in inadequate force to drive the connecting rod reciprocation. Increasing air pressure typically resolves this issue. Additionally, poor air quality can hinder the movement of the linkage rod and reduce motor speed, weakening pump output.

Seal-free self-priming pumps are primarily used for low-level lifting in the wastewater treatment system of the Second Purification Plant, replacing submersible sewage pumps and long-shaft submerged lift pumps in suction tanks. In summary, the use of seal-free self-priming pumps offers simple operation and reduced maintenance workload, making them highly suitable for the wastewater treatment system in natural gas purification plants where safety requirements are critical. Anhui Shengshi Datang now provides an analysis and summary of the usage of seal-free self-priming pumps. 1. Structure and Working Principle of Seal-Free Self-Priming Pumps (1) Basic Structure of Self-Priming Pumps Typically, the basic structure of a self-priming pump mainly includes the following components: a liquid storage chamber, a pump body rotor, inlet and outlet valves, a motor, and several other parts that together form the pump. (2) Basic Working Principle of Seal-Free Self-Priming Pumps The working principle primarily involves the following processes: first, self-priming and exhaust; second, normal pumping of liquid. 2. Analysis of the Practical Usage of Seal-Free Self-Priming Pumps (1) Advantages of Seal-Free Self-Priming Pumps in Low-Level Liquid Transport ① Small seal-free self-priming pumps do not require specialized installation foundations or anchor bolts. They can be placed horizontally, making installation simple. They can easily replace existing lift pumps or submersible pumps. ② Easy operation. Normal operation only requires priming the pump once, after which starting and stopping can be done effortlessly. ③ Strong self-priming capability. Within the suction range, they can replace submersible electric pumps, reducing safety hazards. ④ No sealing required. Completely eliminates leakage, dripping, and seepage. During operation, the sealing device does not experience friction, extending its lifespan by more than 10 times. The self-priming performance is stable and reliable, requiring only one initial priming for lifelong self-priming, with superior self-control capability. ⑤ No need for a separate suction device, resulting in a simpler structure and safer operation. ⑥ Maintenance of seal-free self-priming pumps is convenient. These devices rarely malfunction, are easier to maintain compared to other equipment, and do not require significant financial investment.   (2) Specific Analysis of the Technical Performance of Seal-Free Self-Priming Pumps ① Due to the simple structure of self-priming pumps and the use of dynamic combined airflow sealing, the pump's operation does not affect the sealing device. Compared to long bearings, this device is easier to operate and has a lower probability of issues. ② The device primarily relies on the principle of air-water separation, giving it strong self-priming performance. Especially after using an "air control valve," the siphon phenomenon can be maximally disrupted, achieving the effect of lifelong self-priming. ③ The drawback is that it does not have a high work efficiency and consumes more energy. ④ After starting the self-priming pump, it takes some time before water is discharged. Therefore, designers of pump stations must pay attention to this situation, meaning multiple backup pumps should be prepared. ⑤ When a self-priming pump is used to lift wastewater, certain parameters such as flow rate, head, and suction head must be kept within allowable limits. Otherwise, equipment malfunctions may occur, adversely affecting the pump's smooth operation. ⑥ Based on the basic principle of self-priming pumps, it is essential to ensure that the connections at the water pipe interfaces are properly sealed. If the pump experiences insufficient flow, it may fail to operate smoothly. 3. Technological Innovations (1) Installation of an Air Valve in the Suction Pipeline to Disrupt the Siphon Phenomenon and Retain Sufficient "Priming Liquid" in the Pump Cavity ① In the early stages of using seal-free self-priming pumps, the electric air valves designed by manufacturers were not installed, mainly because they were unsuitable for flammable and explosive environments. Additionally, air valves of this model had many defects, such as frequent malfunctions. Therefore, personnel should use solenoid valves as air valves based on actual application conditions, significantly improving durability and stability. ② Function and Principle of the Electric Air Control Valve The air valve is typically installed at the high point of the self-priming pump's suction pipe. When the pump starts, the solenoid valve is energized, and the valve core seats downward, ensuring the suction pipeline is sealed to achieve self-priming. When the pump stops, the air valve opens, allowing air to enter the pipe cavity. This separates the liquid in the suction pipe and pump cavity, preventing backflow of the liquid in the pump cavity. This completely disrupts the siphon phenomenon, ensuring the self-priming pump operates normally during the next self-priming cycle. The air valve is particularly suitable for self-priming pumps that start and stop frequently, reducing the need for priming operations. (2) Use of Steel Wire Flexible Hoses in the Suction Pipe to Facilitate Daily Maintenance and Troubleshooting of Self-Priming Pumps ① Typically, self-priming pumps in wastewater systems, like other pumps, require regular cleaning at specific intervals. If the suction tank is deep, maintaining metal suction pipes requires collaboration among several personnel. ② If the suction pipe of the self-priming pump operates under negative pressure, such as when pinholes occur, insufficient air may reach the pump, preventing normal operation. Moreover, such issues are not easily detectable. By using steel wire flexible hoses, if leakage points occur, the hose can be pulled back to the ground for inspection promptly. (3) Adjusting the Pump Outlet Diameter to Prevent Motor Overload ① From the perspective of seal-free self-priming pumps, some manufacturers fail to achieve precision during production, resulting in inconsistent power output between the motor and the pump body. This can easily lead to overload situations. ② During specific applications, personnel need to adjust the flow path based on the actual degree of overload to ensure the pump's flow rate remains within allowable limits.

  Centrifugal pumps are widely used in industrial production and engineering systems for conveying various liquid media. However, during operation, a phenomenon that severely affects pump performance and service life often occurs—cavitation. Cavitation not only reduces the efficiency of centrifugal pumps but also causes serious damage to key components such as impellers, and can even lead to the complete scrapping of the equipment. Therefore, studying and understanding the causes of cavitation in centrifugal pumps is of great significance for the rational design, correct installation, and safe operation of pumps. Below, Anhui Shengshi Datang will provide you with a detailed introduction. 1. Basic Concept of Cavitation Cavitation refers to the phenomenon where, as liquid flows through the pump impeller, the local pressure drops below the saturated vapor pressure of the liquid at its operating temperature, causing partial vaporization of the liquid and the formation of numerous tiny vapor bubbles. When these bubbles are carried by the liquid flow into a region of higher pressure, the surrounding pressure rapidly increases, causing the bubbles to collapse instantaneously and condense back into liquid. The collapse of these bubbles generates intense shock waves and localized high temperatures, which impact the impeller surface, leading to fatigue pitting or spalling of the metal. This is the cavitation phenomenon in centrifugal pumps. The essence of cavitation is the result of the combined action of fluid dynamics and thermodynamics. The fundamental cause is the uneven pressure distribution within the liquid. When the local flow velocity is too high or the geometric design is unreasonable, the local pressure drops, triggering the cyclic process of vaporization and bubble collapse. 2. Root Cause of Cavitation The root cause of cavitation in centrifugal pumps is that the local pressure of the liquid within the pump falls below the saturated vapor pressure of the liquid at that temperature. In a centrifugal pump, liquid flows from the suction pipe into the impeller inlet. As the flow passage gradually contracts, the liquid velocity increases, and the static pressure consequently decreases. When the local pressure drops to the saturated vapor pressure of the liquid, the liquid begins to vaporize, generating vapor bubbles. These bubbles are carried into the high-pressure region towards the middle and outlet of the impeller, where they rapidly collapse under the high pressure. The high-energy shock waves released during bubble collapse cause metal erosion on the impeller surface, increased pump vibration, enhanced noise, and problems such as reduced flow rate and head. 3. Main Factors Leading to Cavitation a. Excessive Suction Lift: If the pump is installed too high or the suction liquid level is too low, the pressure on the suction side decreases. As the liquid flows towards the impeller inlet, the pressure drops further. When it falls below the saturated vapor pressure, vaporization occurs. If the suction lift exceeds the allowable NPSH (Net Positive Suction Head), cavitation is inevitable. b. Excessive Suction Line Resistance: A suction pipeline that is too long, too narrow, has too many elbows, or has a partially closed valve causes significant frictional and local pressure losses. The reduced pressure at the suction end leads to a further pressure drop at the impeller inlet, making cavitation more likely. Additionally, air leakage or poor sealing in the suction piping can introduce gas into the liquid, exacerbating cavitation. c. Excessively High Liquid Temperature: An increase in liquid temperature significantly raises its saturated vapor pressure, making the liquid more prone to vaporization. For example, the saturated vapor pressure of water is relatively low at room temperature but increases substantially at high temperatures. Even if the suction pressure remains unchanged, the vaporization condition might be met when the temperature rises, thus triggering cavitation. d. Low Inlet Pressure or Reduced Ambient Pressure: When the pressure at the pump suction source decreases—such as due to a drop in liquid level, a vacuum in the supply container, or low ambient atmospheric pressure (e.g., at high altitudes)—the pressure at the suction port becomes insufficient, making it very easy for the liquid to vaporize at the impeller inlet. e. Improper Pump Design or Installation: The structural design of the pump directly affects its cavitation performance. For instance, an impeller inlet diameter that is too small, an unreasonable blade leading edge angle, or a rough impeller surface can cause unstable liquid flow, leading to a sharp local pressure drop. Furthermore, failure to follow the manufacturer's provided Required NPSH (NPSHr) requirements during installation, or installing the pump at an excessive height, can also lead to cavitation. f. Improper Operating Conditions: When the pump operates at flow rates deviating from the design point, runs for extended periods at low flow, or during sudden valve adjustments, the pressure distribution of the fluid changes, which can also cause local vaporization and cavitation. 4. Effects and Hazards of Cavitation The hazards of cavitation to centrifugal pumps are mainly manifested in the following aspects: a. Metal Surface Damage: The high-pressure shocks generated by collapsing bubbles cause pitting erosion on the impeller surface. Long-term development can lead to material fatigue, spalling, and even perforation of the impeller. b. Performance Degradation: Cavitation leads to a significant reduction in flow rate, head, and efficiency, altering the pump's characteristic curves. c. Vibration and Noise: The impact forces generated by cavitation cause mechanical vibration and high-frequency noise, affecting the stable operation of the equipment. d. Reduced Service Life: Long-term operation under cavitation conditions accelerates mechanical wear, shortening the service life of bearings, seals, and the impeller. 5. Measures to Prevent Cavitation To prevent or mitigate cavitation, measures should be taken from the perspectives of design, installation, and operation: a. Select a reasonable installation height to ensure sufficient pressure on the suction side, making the Available NPSH (NPSHa) greater than the pump's Required NPSH (NPSHr). b. Optimize the suction pipeline by shortening its length, reducing the number of elbows, increasing the pipe diameter, keeping suction valves fully open, and avoiding air ingress. c. Control the liquid temperature through cooling or lowering the storage tank temperature to reduce the liquid's saturated vapor pressure. d. Increase the inlet pressure, for example, by installing a booster pump, pressurizing the liquid surface, or placing the liquid container at a higher elevation. e. Improve the impeller structure by using materials and geometries with good anti-cavitation properties, such as adding an inducer or optimizing the blade inlet angle. f. Keep the pump operating near its design point, avoiding prolonged operation at low flow rates or other abnormal operating conditions. In summary, the occurrence of cavitation in centrifugal pumps is primarily caused by the pressure of the liquid at the impeller inlet being too low, falling below its saturated vapor pressure, which triggers vaporization and subsequent bubble collapse. Specific factors leading to this phenomenon include excessive suction lift, excessive suction resistance, high liquid temperature, low inlet pressure, and improper design or operation. Cavitation not only affects pump performance but also causes severe damage to the equipment. Therefore, in both design and operation, emphasis must be placed on the prevention and control of cavitation. By rationally configuring the system, optimizing structural parameters, and improving operating conditions, the safe and efficient operation of centrifugal pumps can be ensured.  

Anhui Shengshi Datang Pump Industry will analyze the working principles and components of vertical axial flow pumps and provide a detailed description of the optimal maintenance and inspection methods for different components, offering reference for the daily maintenance and inspection of vertical axial flow pumps.   Basic Working Principle of Vertical Axial Flow Pumps The fundamental principle of the vertical axial flow pump primarily utilizes the lift force from aerodynamics. Lift force on an airfoil is generated due to the pressure difference between the upper and lower surfaces. When fluid flows over the airfoil, both streamlines and streamtubes change, consequently causing corresponding changes in the pressure around the airfoil. As long as a pressure difference exists between the upper and lower surfaces, lift is generated. The blades and impeller casing of the vertical axial flow pump are made of cast steel with good corrosion resistance and strong wear resistance. During the design of vertical axial flow pumps, considering the convenience of maintenance and repair, the casing is designed to split along the centerline. The core component of the vertical axial flow pump is the runner, which performs work on the liquid to convert electrical energy into the gravitational potential energy of the fluid (i.e., the Yellow River water), enabling the fluid to reach the required design height. The guide vane body, which supports the rubber bearings, primarily converts the fluid's potential energy into hydraulic energy within the system. It supports the intermediate seat, a relatively important part of the equipment, and plays a significant role in ensuring the normal and orderly operation of the vertical axial flow pump. The elbow's main function is to guide the flow, and the thrust bearing assembly primarily undertakes a certain amount of the axial force.   Inspection and Maintenance of Vertical Axial Flow Pumps 1. Packing Inspection and Maintenance When inspecting and maintaining the packing in a vertical axial flow pump, the focus is primarily on checking the material of the packing. The steps can be roughly summarized as follows: ① Dismantle the packing; ② Perform a pull test by hand; ③ Check if the packing shows breakage; replace any packing that is found broken or cracked promptly. In daily maintenance, note that packing can generally only be reused once; timely replacement helps prevent leakage issues. 2. Upper and Lower Journal Bearing Inspection and Maintenance Through long-term inspection and maintenance of vertical axial flow pumps, it has been found that journal bearings are extremely prone to damage. For instance, during the operation of the pump, frequent maintenance often reveals large areas of wear on the journal bearings. The designed service life of journal bearings is about 3 years. During their normal operation, they need to be inspected and maintained regularly. The general steps for performing journal bearing inspection are as follows: ① Pull out the shaft from the bearing; ② Wipe with a lint-free cloth soaked in red dye (or inspection oil) and observe for any scratches, embedded abrasive particles, or signs of burning/scoring; ③ If severe scratches or burning marks are present, the journal bearing needs replacement. Although the design life of journal bearings is around 3 years, in practice, after about one year of use, problems frequently occur, necessitating adjustment of the concentricity and performing horizontal alignment correction on the pump shaft. Because the bearing installation typically has a fit clearance with the shaft of (0.2~0.6)mm. If this distance is too small (<0.2 mm), it can cause the shaft to seize, affecting the normal starting of the motor. If the distance is too large (>0.6 mm), it can lead to shaft imbalance, resulting in severe vibration. During the daily maintenance of journal bearings, attention should be paid to the regular addition of lubricating oil, which can reduce bearing wear and prevent corrosion. 3. Thrust Bearing Pad Inspection and Maintenance When inspecting and maintaining the thrust bearing pads, the first step is a general visual inspection to check if the surface smoothness meets standards. Visually inspect the pad surface for wear scratches or burning marks. At the same time, it is necessary to check whether each pad is bearing load evenly. This load check is done by visually observing the "peach-blossom" pattern wear on the pad surface. If the "peach-blossom" wear pattern appears relatively uniform, it indicates that the load on the pads is relatively balanced. Otherwise, if the pattern appears messy, it indicates an unbalanced load. If the load is unbalanced, the position of the rotating shaft needs adjustment to bring it to a relatively horizontal position. The general steps for repairing worn thrust pads are as follows: ① Remove the pads in sequence and mark them; ② Clean the pads and keep them dry; ③ Use a surface plate to scrape/scrape the pad surface; ④ Visually inspect the smoothness of the contact area on the pad surface; ⑤ If obvious high spots exist, use a triangular scraper to treat the surface until the "peach-blossom" contact pattern reaches a uniformly flat state, completing the repair work. After the above work, it is necessary to remove debris from the thrust bearing housing and surrounding areas, so clean the housing with gasoline. After cleaning, reassemble according to the marked sequence. 4. Bearing Sleeve/Bushing Inspection and Maintenance When inspecting and maintaining the bearing sleeve/bushing, first visually inspect the sleeve surface for scratches. For sleeves with scratches, first use sandpaper for polishing. If the extent of scratching is beyond repairable limits, the bearing sleeve needs prompt replacement. The general replacement steps are: ① Clean the bearing, and after cleaning, apply lubricating oil; ② Dismantle and inspect the bearing; ③ Clean the new bearing sleeve and visually inspect to ensure the inner surface is smooth; if not smooth, perform sandpaper polishing; ④ Heat the inner wall using a 1kW tungsten lamp (or similar heat source); ⑤ Once the bearing sleeve reaches the specified temperature standard, quickly install it onto the shaft, and wait for the sleeve to cool down to room temperature. 5. Blade and Impeller Inspection and Maintenance When inspecting blades, visual inspection is generally used to observe if there are any holes, missing corners, or cavitation pits/spots on the blades. If defects are found, new blades need to be replaced promptly. When replacing blades, pay attention to align the blade's index line with the impeller's angle line. After installing the blades, perform a static balance test on the impeller assembly. Only after the static balance test meets the requirements can the entire assembly be installed onto the shaft.

  Regarding the demagnetization issue of magnetic drive pumps discussed in the last session, in this session, Anhui Shengshi Datang will provide some protective measures. Improvement Measures for Magnetic Drive Pump Demagnetization 1. Improvement Approach When improving the demagnetization situation of magnetic drive pumps, the primary focus is on enhancing the cooling aspect of lubrication to prevent the vaporization of the friction fluid, which leads to dry friction. However, it is also necessary to consider that the conveyed medium may contain vaporizable and volatile substances. According to the law of energy conservation, the velocity of the conveyed medium can be comprehensively reduced, and the static pressure can be increased to enhance the vaporization degree of the medium, thereby effectively preventing vaporization due to excessive temperature. Based on this improvement approach, comprehensive enhancements can be made to the impeller and bearing areas of the magnetic drive pump. 2. Improvement Measures (1) The bearing of the magnetic drive pump needs to be changed from semi-hollow to fully hollow, and the return hole should be completely drilled through to become a through hole, effectively increasing the actual flow rate of the medium for cooling and lubrication. (2) During installation, it is essential to ensure that the rotation directions of the spiral grooves match each other. The function of the spiral grooves is to provide flushing and lubrication for the medium. Therefore, the rotation direction of the spiral grooves must be clearly indicated to ensure smoother flow of the medium. During high-speed rotation, some heat will be carried away, thereby enhancing the cooling and lubrication effects on the bearings and thrust rings and promoting the formation of a liquid protective film during friction. (3) The impeller section needs to be trimmed, but it must be ensured that the impeller efficiency remains unchanged. Trimming the impeller not only reduces the fluid flow velocity but also comprehensively enhances the vaporization degree of the medium through static pressure, improving the vaporization effect. At the same time, the operating range of the magnetic drive pump needs to be expanded to reduce the vibration impact of the process during operation. (4) A protection device needs to be installed in the magnetic drive pump. During operation, if any component is overloaded or the inner magnetic rotor gets stuck in the "bearing seizure" condition, the protection device can cause it to automatically disengage, providing comprehensive protection for the magnetic drive pump. Operational Considerations for Magnetic Drive Pumps To fundamentally resolve the demagnetization issue of magnetic drive pumps, in addition to comprehensive improvements, the following points must be noted during operation: 1. Before starting the magnetic drive pump, priming must be performed to ensure no air or gas remains inside the pump. 2. The bearings of the magnetic drive pump rely on the conveyed medium for cooling and lubrication. Therefore, it is essential to ensure that the magnetic drive pump does not run dry or that all medium is cleared, as this could cause bearing failure due to dry friction or a sudden significant temperature rise inside the pump, leading to demagnetization of the inner magnetic rotor. 3. If the conveyed medium contains particulate matter, a filter screen must be installed at the pump inlet to prevent excessive debris from entering the magnetic drive pump. 4. Components such as the rotor and crankshaft have strong magnetic properties. During installation and removal, the magnetic field scope must be fully considered. Otherwise, it may affect nearby electronic equipment. Therefore, installation and removal must be performed at a distance from electronic devices. 5. During operation of the magnetic drive pump, no objects should come into contact with the outer magnetic rotor to avoid damage and other issues. 6. The outlet valve must not be closed during the operation of the magnetic drive pump, as this could damage components such as the bearings and magnetic steel. If the pump continues to operate normally after the outlet valve is closed, this time must be controlled within 2 minutes to prevent demagnetization. 7. The inlet pipeline valve should not be used to control the flow rate of the medium, as this may cause cavitation. 8. After the magnetic drive pump has been in continuous operation for a certain period, it should be appropriately stopped. After confirming that the wear on the bearings and thrust rings is not severe, disassemble them to inspect the internal components. If minor issues are found in any components, replace them immediately. In addition to the above considerations, here are some supplementary points: A. Root Cause: In-Depth Understanding of Demagnetization Mechanism The magnetic coupler of a magnetic drive pump consists of an inner magnetic rotor and an outer magnetic rotor. When the inner magnetic rotor overheats due to insufficient cooling and lubrication, or when abnormal conditions (such as dry friction or cavitation) cause a sharp temperature rise, once the Curie temperature of permanent magnet materials like NdFeB (typically between 110°C - 150°C) is reached, their magnetism will sharply decline or even permanently disappear. Therefore, the ultimate goal of all measures is to ensure that the inner magnetic rotor always remains below a safe temperature. B. Preventive Measures During Design and Selection (Source Control) The following aspects are crucial when purchasing or improving magnetic drive pumps: 1. Selecting Appropriate Magnetic Material and Protection Grade: a. Neodymium Iron Boron (NdFeB): High magnetic energy product, but relatively low Curie temperature and prone to corrosion. Must ensure complete encapsulation (e.g., stainless steel sleeve) and good cooling. b. Samarium Cobalt (SmCo): Slightly lower magnetic energy product, but higher Curie temperature (can exceed 300°C), better thermal stability, and more corrosion-resistant. For high-temperature conditions or applications requiring high reliability, SmCo magnets should be prioritized. c. Inquire with Suppliers: Clarify the magnet material, grade, and Curie temperature. 2. Providing Accurate Operating Parameters: During selection, it is essential to provide the manufacturer with accurate medium characteristics (including composition, viscosity, solid particle content, and size), operating temperature, inlet pressure, flow range, etc. This helps the manufacturer select the most suitable pump type, materials, and cooling flow path design for your needs. 3. Consider Installing a Temperature Monitoring System: a. Isolation Sleeve Temperature Monitoring: Install temperature sensors (e.g., PT100) on the outer wall of the isolation sleeve. Since the inner magnetic rotor temperature is difficult to measure directly, the isolation sleeve temperature is the most direct reflection. Setting high-temperature alarms and shutdown interlocks is the most effective automated means to prevent demagnetization. b. Bearing Monitoring: Advanced magnetic drive pumps can be equipped with bearing wear monitors to provide early warnings before severe wear leads to temperature rise.   C. Key Supplementary Considerations in Operation and Maintenance In addition to the mentioned priming, preventing dry running, and avoiding cavitation, the following should also be noted: 1. Minimum Continuous Stable Flow and Cooling Circuit: a. Magnetic drive pumps have a minimum continuous stable flow. Operating below this flow rate means the heat carried away by the internal medium circulation is insufficient, leading to temperature buildup. b. It is essential to ensure that the pump's cooling return line (if equipped) is unobstructed. This line not only provides bearing lubrication but is also a lifeline for cooling the inner magnetic rotor. This line must never be closed or blocked. 2. Avoid "Low Flow" Operation: Prolonged operation near the low flow point results in low efficiency, with most of the work converted into heat, similarly causing medium temperature rise and increasing demagnetization risk. Ensure the pump operates within its efficient range. 3. System Pressure and Net Positive Suction Head (NPSH): a. Ensure Sufficient Inlet Pressure: The mentioned increase in static pressure to enhance vaporization essentially means increasing the Available NPSH (NPSHa) to be significantly greater than the pump's Required NPSH (NPSHr). This is fundamental to preventing cavitation, as the vibration and localized high temperatures generated by cavitation pose a dual threat to magnetic drive pumps. b. Monitor Inlet Filters: For media containing impurities, the inlet filter must be cleaned regularly. Clogging can cause inlet pressure drop, inducing cavitation. 4. Contingency Plans for Abnormal Conditions: a. Power Interruption: If a factory experiences a sudden power outage followed by a quick restoration, be cautious as the medium in the system may have partially vaporized or the pump may have accumulated air. In such cases, follow the initial startup steps for inspection and priming; do not start directly. b. Hot Medium Transfer: When conveying easily vaporizable media, consider insulating the inlet pipeline and even cooling the pump body (e.g., adding a cooling water jacket) to ensure the medium remains in liquid state upon entering the pump. D. Deepening Maintenance and Inspection 1. Regular Disassembly Inspection: In addition to checking bearing and thrust ring wear, focus on inspecting the isolation sleeve and inner magnetic rotor surfaces. Any scratches or wear points may indicate poor cooling or misalignment. Check the magnetic strength of the inner magnetic rotor (using a Gauss meter), establish historical data records, and track its magnetic decay trend. 2. Management of Standby Pumps: The inner magnetic rotor of a magnetic drive pump stored as a long-term standby might experience slight demagnetization due to surrounding stray magnetic fields or vibrations. Regularly rotate the pump and alternate its use.

Magnetic pumps are commonly used pumps, and demagnetization is a relatively frequent cause of damage. Once demagnetization occurs, many people may find themselves at a loss, which could lead to significant losses in work and production. To prevent such situations, Anhui Shengshi Datang will briefly explain today why magnetic pumps experience demagnetization.   1. Magnetic Pump Structure and Principle 1.1 Overall Structure The main components of a magnetic pump's overall structure include the pump, the motor, and the magnetic coupler. Among these, the magnetic coupler is the key component, encompassing parts such as the containment shell (isolating can) and the inner and outer magnetic rotors. It significantly impacts the stability and reliability of the magnetic pump.   1.2 Working Principle A magnetic pump, also known as a magnetically driven pump, operates primarily on the principle of modern magnetism, utilizing the attraction of magnets to ferrous materials or the magnetic force effects within magnetic cores. It integrates three technologies: manufacturing, materials, and transmission. When the motor is connected to the outer magnetic rotor and the coupling, the inner magnetic rotor is connected to the impeller, forming a sealed containment shell between the inner and outer rotors. This containment shell is firmly fixed to the pump cover, completely separating the inner and outer magnetic rotors, allowing the conveyed medium to be transmitted into the pump in a sealed manner without leakage. When the magnetic pump starts, the electric motor drives the outer magnetic rotor to rotate. This creates attraction and repulsion between the inner and outer magnetic rotors, driving the inner rotor to rotate along with the outer rotor, which in turn rotates the pump shaft, accomplishing the task of conveying the medium. Magnetic pumps not only completely solve the leakage problems associated with traditional pumps but also reduce the probability of accidents caused by the leakage of toxic, hazardous, flammable, or explosive media.   1.3 Characteristics of Magnetic Pumps (1) The installation and disassembly processes are very simple. Components can be replaced anywhere at any time, and significant costs and manpower are not required for repair and maintenance. This effectively reduces the workload for relevant personnel and substantially lowers application costs. (2) They adhere to strict standards in terms of materials and design, while requirements for technical processes in other aspects are relatively low. (3) They provide overload protection during the conveyance of media. (4) Since the drive shaft does not need to penetrate the pump casing, and the inner magnetic rotor is driven solely by the magnetic field, a completely sealed flow path is truly achieved. (5) For containment shells made of non-metallic materials, the actual thickness is generally below about 8 mm. For metallic containment shells, the actual thickness is below about 5 mm. However, due to the thick inner wall, they will not be punctured or worn through during the operation of the magnetic pump.   2. Main Causes of Demagnetization in Magnetic Pumps 2.1 Operational Process Issues Magnetic pumps represent relatively new technology and equipment, requiring high technical proficiency during application. After demagnetization occurs, operational and process aspects should first be investigated to rule out problems in these areas. The investigation content includes six parts: (1) Check the magnetic pump's inlet and outlet pipelines to ensure there are no issues with the process flow. (2) Check the filter device to ensure it is free of any debris. (3) Perform priming and venting of the magnetic pump to ensure no excess air remains inside. (4) Check the liquid level in the auxiliary feed tank to ensure it is within the normal range. (5) Check the operator's actions to ensure no errors occurred during operation. (6) Check the maintenance personnel's operations to ensure they complied with relevant standards during maintenance.   2.2 Design and Structural Issues After thoroughly investigating the above six aspects, a comprehensive analysis of the magnetic pump's structure is necessary. The sliding bearings play a cooling role when the magnetic pump conveys the medium. Therefore, it is essential to ensure sufficient medium flow rate to effectively cool and lubricate the gap between the containment shell and the sliding bearings, and the friction between the thrust ring and the shaft. If there is only one return hole for the sliding bearings and the pump shaft is not interconnected with the return hole, the cooling and lubrication effect can be reduced. This prevents complete heat removal and hinders maintaining a good state of liquid friction. Ultimately, this can lead to seizure of the sliding bearings (bearing lock-up). During this process, the outer magnetic rotor continues to generate heat. If the inner magnetic rotor's temperature remains within the limit, the transmission efficiency decreases but can potentially be improved. However, if the temperature exceeds the limit, it cannot be remedied. Even if it cools down after shutdown, the reduced transmission efficiency cannot recover to its original state, eventually causing the magnetic properties of the inner rotor to gradually diminish, leading to demagnetization of the magnetic pump.   2.3 Medium Properties Issues If the medium conveyed by the magnetic pump is volatile, it can vaporize when the internal temperature rises. However, both the inner magnetic rotor and the containment shell generate high temperatures during operation. The area between them also generates heat due to being in a vortex state, causing the internal temperature of the magnetic pump to rise sharply. If there are issues with the magnetic pump's structural design, affecting the cooling effect, then when the medium is delivered into the pump, it may vaporize due to the high temperature. This causes the medium to gradually turn into gas, severely affecting the pump's operation. Additionally, if the static pressure of the conveyed medium within the magnetic pump is too low, the vaporization temperature decreases, inducing cavitation. This can halt the medium conveyance, ultimately causing the magnetic pump bearings to burn out or seize due to dry friction. Although the pressure at the impeller varies during operation, centrifugal force effects can cause very low static pressure at the pump inlet. When the static pressure falls below the vapor pressure of the medium, cavitation occurs. When the magnetic pump contacts the cavitating medium, if the cavitation scale is small, it might not significantly affect the pump's operation or performance noticeably. However, if the medium's cavitation expands to a certain scale, a large number of vapor bubbles form inside the pump, potentially blocking the entire flow path. This stops the flow of medium inside the pump, leading to dry friction conditions due to the ceased flow. If the pump's structural design results in an inadequate cooling effect, the containment shell temperature can become excessively high and cause damage, subsequently increasing the temperature of both the medium and the inner magnetic rotor.

  In the previous section, we discussed the causes of centrifugal pump cavitation. Below, Anhui Shengshi Datang will introduce measures to prevent centrifugal pump cavitation. 1. Improvements in Design and Materials From the perspectives of design and materials, the following measures can be taken to prevent or mitigate the hazards of centrifugal pump cavitation: A. Gap Optimization Design: Appropriately increase the clearance between moving parts, especially between the impeller and the pump casing, and between the seal ring and the shaft, to reduce the risk of seizing due to thermal expansion. Research shows that increasing the standard clearance by 15%-20% can significantly reduce the probability of seizing during cavitation, with minimal impact on pump efficiency. B. Material Selection and Treatment:   a. Perform tempering heat treatment on the pump shaft to improve its hardness and wear resistance, reducing deformation and wear during cavitation.   b. Select materials with low thermal expansion coefficients, such as stainless steel or special alloys, to minimize clearance changes caused by thermal expansion.   c. Apply wear-resistant coatings like hard alloy or use ceramic materials for key friction parts such as seal rings to enhance wear resistance. C. Sealing System Improvements:   a. Use mechanical seals that do not rely on the pumped medium for lubrication, such as gas-lubricated mechanical seals or double mechanical seals.  b. Configure external lubrication systems to provide lubrication for the seal faces even when the pump is cavitating.  c. For packing seals, use self-lubricating packing, such as composite packing containing PTFE.   D. Bearing System Optimization:  a. Use enclosed self-lubricating bearings to reduce dependence on external cooling.  b. Add independent cooling systems for bearings to ensure normal bearing temperature is maintained even during pump cavitation.  c. Select bearings and lubricants with higher temperature tolerance. E. Pump Cavity Design Improvements:  a. For special applications, design a water storage space so that the pump can maintain a minimum liquid volume even during short-term water shortage.  b. Self-priming pumps are typically designed with a larger pump cavity volume and specialized gas-liquid separation devices, allowing them to better handle short-term cavitation. Practice shows that reasonable design and material selection can reduce the risk of damage during centrifugal pump cavitation by over 50%, while also extending the overall service life of the equipment. 2. Application of Monitoring and Control Systems Modern monitoring and control technologies provide effective means to prevent centrifugal pump cavitation: A. Cavitation Detection Systems:  a. Flow Monitoring: Install a flow meter at the pump outlet to automatically alarm or shut down the pump when the flow rate falls below a set value.  b. Current Monitoring: Motor load decreases during cavitation, leading to a significant drop in current; cavitation can be detected by monitoring current changes.  c. Pressure Monitoring: A sudden drop or increased fluctuation in outlet pressure is a key indicator of cavitation.  d. Temperature Monitoring: Abnormal temperature rises in mechanical seals, bearings, or the pump body can indirectly reflect the cavitation state. B. Liquid Level Control Systems:  a. Install level sensors in water tanks, sumps, and other intake facilities to automatically stop the pump when the level falls below a safe value.  b. For special occasions, set up dual-level protection: low-level alarm and very low-level forced pump shutdown.  c. Use non-contact level gauges (e.g., ultrasonic, radar) to avoid potential jamming issues associated with traditional float switches. C. Integrated Intelligent Control Systems:  a. Integrate multiple parameters (flow, pressure, temperature, level) into a PLC or DCS system to more accurately identify cavitation status through logical judgment.  b. Set up two levels of protection: cavitation warning and cavitation alarm. The system can attempt to automatically adjust operating conditions during a warning and force a shutdown during an alarm.  c. Use expert systems or artificial intelligence technology to predict potential cavitation risks in advance through historical data analysis. D. Remote Monitoring and Management:  a. Utilize IoT technology to achieve remote monitoring of pump stations, enabling timely detection of abnormalities.  b. Establish fault prediction models to provide early warnings of potential cavitation risks through big data analysis.  c. Set up automatic recording and reporting systems to log changes in operating parameters, providing a basis for fault analysis. Data shows that centrifugal pumps equipped with modern monitoring and control systems experience over 85% fewer cavitation incidents compared to traditional equipment, with significantly reduced maintenance costs. The value of these systems is particularly evident in unattended pump stations.     3. Operating Procedures and Maintenance Management Scientific operating procedures and maintenance management are crucial links in preventing centrifugal pump cavitation: A. Pre-Startup Checks and Preparation:  a. Confirm that valves on the suction line are fully open and filters are not clogged.  b. Check the sealing of the pump casing and pipelines to ensure there are no air leakage points.  c. Ensure the pump is fully primed and air is completely vented before the first startup or after a prolonged shutdown.  d. Manually rotate the pump shaft several turns to ensure it rotates flexibly without abnormal resistance. B. Correct Startup and Shutdown Procedures:  a. Open the suction valve first, then the discharge valve, avoiding starting against a closed discharge valve.  b. For large pumps, start with the discharge valve slightly open, then fully open it once operation stabilizes.  c. When stopping the pump, close the discharge valve first, then the motor, and finally the suction valve to prevent backflow and water hammer.  d. Drain liquid from the pump casing promptly after shutdown in cold winter regions to prevent freezing. C. Monitoring and Management During Operation:  a. Establish an operating log system to regularly record parameters such as flow, pressure, temperature, and current.  b. Implement an inspection round system to promptly detect abnormal noise, vibration, or leaks.  c. Avoid prolonged operation at low flow rates; install a minimum flow bypass line if necessary.  d. For multi-pump parallel systems, ensure reasonable load distribution among pumps to avoid single pump overload or cavitation. D. Regular Maintenance and Inspection:  a. Regularly clean suction line filters to prevent clogging.  b. Check the condition of mechanical seals or packing seals, and replace aged or damaged parts promptly.  c. Regularly check bearing temperature and lubrication status, adding or replacing lubricant as required.  d. Periodically measure seal ring clearances to ensure they are within allowable limits.  e. Check that balance pipes and balance holes are clear (applicable to multi-stage pumps). E. Personnel Training and Management:  a. Provide professional training for operators and maintenance personnel to improve their ability to identify and handle faults.  b. Formulate clear responsibility systems and emergency plans to ensure a rapid response in case of abnormalities.  c. Establish experience sharing mechanisms to promptly summarize and disseminate fault handling experiences. Practice proves that sound operating procedures and maintenance management can reduce unplanned downtime of centrifugal pumps by over 70%, significantly improving equipment reliability and service life.     4. Response Measures for Emergency Situations Despite various preventive measures, centrifugal pump cavitation may still occur under special circumstances. In such cases, emergency response measures are needed to minimize losses: A. Rapid Identification and Shutdown:  a. If signs of cavitation such as abnormal noise, increased vibration, or a sudden drop in discharge pressure are detected, the pump should be shut down immediately for inspection.  b. For critical equipment, emergency stop buttons can be installed to halt the pump immediately upon detecting abnormalities.  c. Do not repeatedly start the pump before confirming and eliminating the cause of cavitation, to avoid exacerbating damage. B. Emergency Cooling Measures:  a. If the pump body is found to be overheated but serious damage has not yet occurred, external cooling measures can be taken, such as wrapping the pump body with wet cloths or applying slight water spray cooling (taking care to avoid electrical components).  b. Do not immediately cool overheated bearings with cold water, to prevent damage from thermal stress. C. Restoring Normal Liquid Supply:  a. Check and clear blockages in the inlet pipeline.  b. For insufficient liquid level, promptly replenish the water source or lower the pump's installation height.  c. Check and repair air leakage points in the pipeline system. D. Special Monitoring After Restart:  a. When restarting the pump after a cavitation event, pay special attention to whether the seal is leaking, if the bearing temperature is normal, and if vibration is within allowable limits.  b. Only resume normal operation after confirming all parameters are normal.  c. It is recommended to increase the frequency of inspection rounds temporarily to ensure stable equipment operation. E. Damage Assessment and Repair:  a. Pumps that have experienced severe cavitation should undergo a comprehensive inspection to assess the extent of damage.  b. Replace damaged components if necessary, such as mechanical seals, seal rings, and bearings.  c. Inspect the impeller and pump casing for damage caused by cavitation. Through timely and effective emergency handling, losses caused by cavitation can be minimized. Statistics show that reasonable emergency measures can reduce equipment recovery time by over 50% in emergency situations, while also reducing the risk of secondary damage.

Working Principle of Centrifugal Pumps The working principle of centrifugal pumps is based on the action of centrifugal force. When the impeller rotates at high speed, the liquid is thrown from the center of the impeller to the outer edge under the influence of centrifugal force, thereby gaining kinetic energy and pressure energy. The specific working process is as follows: 1.Liquid enters the central area of the impeller through the pump's suction inlet. 2.The rotation of the impeller generates centrifugal force, causing the liquid to move from the center of the impeller to the outer edge along the blade passages. 3.The liquid gains kinetic energy and pressure energy within the impeller and is then discharged into the pump casing. 4.Inside the pump casing, part of the liquid's kinetic energy is converted into pressure energy, and the liquid is ultimately discharged through the outlet. During the operation of a centrifugal pump, the impeller does work by converting mechanical energy into the energy of the liquid. As the liquid flows through the impeller, both its pressure and velocity increase. According to Bernoulli's equation, the increase in the total energy of the liquid is primarily manifested as an increase in pressure energy, enabling the centrifugal pump to transport the liquid to a higher elevation or overcome greater system resistance. It is important to note that the prerequisite for the normal operation of a centrifugal pump is that the pump cavity must be filled with liquid. This is because centrifugal force can only act on liquids and not on gases. If air is present in the pump cavity, the pump will be unable to build up pressure normally, resulting in "vapor lock," which ultimately leads to cavitation. Analysis of Causes for Centrifugal Pump Cavitation  1.Inadequate Inlet Medium or Insufficient Inlet Pressure Inadequate inlet medium is one of the most common causes of centrifugal pump cavitation. The following situations may lead to insufficient inlet medium: a. Low Liquid Level: When the liquid level in a pool, tank, or storage container falls below the pump's suction pipe or the minimum effective level, the pump may draw in air instead of liquid, resulting in cavitation. b. Excessive Suction Lift: For non-self-priming centrifugal pumps, if the installation height exceeds the allowable suction lift, even if the suction pipe is immersed in the liquid, the pump will be unable to draw the liquid up, leading to a lack of liquid inside the pump. According to physical principles, the theoretical maximum suction lift for non-self-priming centrifugal pumps is approximately 10 meters of water column (atmospheric pressure value). However, considering various losses, the actual suction lift is typically below 6-7 meters. c. Insufficient Inlet Pressure: In applications requiring positive inlet pressure, if the provided inlet pressure is lower than the required value, the pump may experience inadequate liquid supply, causing cavitation. d. Poor System Design: In some system designs, if the suction pipeline is too long, the pipe diameter is too small, or there are too many bends, the pipeline resistance increases, reducing the inlet pressure and preventing the centrifugal pump from drawing liquid properly. Case studies show that approximately 35% of centrifugal pump failures in the petrochemical industry are caused by inadequate inlet medium or insufficient inlet pressure. This issue is particularly common in oil transportation systems due to the high viscosity and vapor pressure of oil products.    2.Blockage in the Inlet Pipeline Blockage in the inlet pipeline is another common cause of centrifugal pump cavitation. Specific manifestations include: a. Clogged Screens or Filters: During long-term operation, screens or filters in the inlet pipeline may become gradually blocked by impurities or sediments, restricting liquid flow. b. Scale Formation Inside the Pipeline: Particularly when handling hard water, water with high calcium and magnesium ion content, or specific chemical liquids, scale or crystalline deposits may form on the inner walls of the pipeline, reducing the effective diameter over time. c. Foreign Object Entry: Accidental entry of objects such as leaves, plastic bags, or aquatic plants into the suction pipeline can block elbows or valves, obstructing liquid flow. d. Partially Closed Valves: Operational errors, such as failing to fully open valves in the suction pipeline, or internal valve malfunctions, can also lead to insufficient flow. e. Foot Valve Failure: In systems equipped with foot valves, if the foot valve malfunctions (e.g., spring deformation or sealing surface damage), it can affect the pump's ability to draw liquid properly. Statistical data indicate that approximately 25% of centrifugal pump cavitation cases in municipal water supply and drainage systems are caused by inlet pipeline blockages. This issue is especially common in wastewater treatment systems with high levels of suspended solids.      3.Incomplete Air Removal from the Pump Cavity Incomplete air removal from the pump cavity is a significant cause of centrifugal pump cavitation. Key manifestations include: a. Inadequate Priming Before Initial Startup: After initial installation or prolonged shutdown, centrifugal pumps must be primed to remove air from the pump body. If priming is insufficient, residual air can prevent the pump from establishing normal working pressure. b. Insufficient Self-Priming Capability: Non-self-priming centrifugal pumps cannot expel air on their own and rely on external priming. While some self-priming pumps have a certain self-priming capability, improper startup methods or excessive self-priming height can lead to poor air expulsion. c. Air Leaks in the Pipeline System: Minor cracks in suction pipeline connections, sealing points, or aging pipes can allow air to enter the system under negative pressure. This is particularly hazardous because even if the pump is initially primed correctly, air can accumulate over time, eventually causing cavitation. d. Seal Failure: Worn or improperly installed shaft seals (e.g., mechanical seals or packing seals) can allow external air to enter the pump, especially when the suction side pressure is below atmospheric pressure. In industrial applications, approximately 20% of centrifugal pump cavitation cases are caused by incomplete air removal from the pump cavity. This issue is particularly common during initial startup after installation or maintenance.    4.Other Causes In addition to the main causes mentioned above, other factors can also lead to centrifugal pump cavitation: a. Liquid Vaporization: When handling high-temperature or highly volatile liquids, if the suction pipeline pressure falls below the liquid’s saturation vapor pressure at that temperature, the liquid may vaporize, forming bubbles. This can prevent the pump from drawing liquid or cause cavitation. b. Operational Errors: Human factors, such as incorrect valve operation or failure to follow startup procedures, can lead to pump cavitation. c. Control System Malfunctions: In automated control systems, failures in level sensors, pressure sensors, or errors in PLC programming logic may cause the pump to start or operate under inappropriate conditions, resulting in cavitation. d. Power or Motor Issues: Incorrect power phase sequence causing motor reversal can prevent the pump from drawing liquid properly. Voltage instability causing motor speed fluctuations can also disrupt normal pump operation. e. Temperature Effects: In extreme environmental conditions, such as cold regions, inadequate insulation may cause liquid in the pipeline to freeze, obstructing flow. In high-temperature environments, liquids may vaporize, forming vapor locks. Research indicates that these other causes account for approximately 20% of centrifugal pump cavitation cases. Although the proportion is relatively small, they can be significant factors in specific scenarios or conditions and should not be overlooked.

Comprehensive Guide to Chemical Centrifugal Pumps: From Features to Installation   1.Overview of Chemical Centrifugal Pumps Chemical centrifugal pumps, as reliable assistants in the chemical industry, have gained widespread popularity due to their outstanding performance characteristics, such as wear resistance, uniform water output, stable operation, low noise, easy adjustment, and high efficiency. Their working principle involves the generation of centrifugal force when the impeller rotates while the pump is filled with water. This force pushes the water in the impeller channels outward into the pump casing. Subsequently, the pressure at the center of the impeller gradually decreases until it falls below the pressure in the inlet pipe. Under this pressure differential, water from the suction pool continuously flows into the impeller, enabling the pump to sustain water suction and supply. With the growing demand for chemical centrifugal pumps across various industries, it is essential to delve into their technical details. Next, Anhui Shengshi Datang will explore 20 technical questions and answers about chemical centrifugal pumps with you, unveiling the technical mysteries behind them.   2.Performance Characteristics of Chemical Centrifugal Pumps Chemical centrifugal pumps are highly favored for their wear resistance, uniform water output, and other features. They possess multiple characteristics, including adaptability to chemical process requirements, corrosion resistance, tolerance to high and low temperatures, resistance to wear and erosion, reliable operation, minimal or no leakage, and the ability to transport liquids in critical states.   3.Technical Details of Chemical Centrifugal Pumps a. Definition and Classification Chemical centrifugal pumps are devices that generate centrifugal force through impeller rotation and can be classified into vane pumps, positive displacement pumps, etc. Based on their working principles and structures, chemical pumps are categorized into vane pumps, positive displacement pumps, and other forms. Vane pumps utilize the centrifugal force generated by impeller rotation to enhance the mechanical energy of liquids, while positive displacement pumps transport liquids by altering the working chamber volume. Additionally, there are special types like electromagnetic pumps, which use electromagnetic effects to transport conductive liquids, as well as jet pumps and airlift pumps that utilize fluid energy to convey liquids.   b. Advantages and Performance Parameters Centrifugal pumps offer high flow rates, simple maintenance, and core metrics such as output power and efficiency. Centrifugal pumps exhibit several notable advantages in application. First, their single-unit output provides a large and continuous flow without pulsation, ensuring smooth operation. Second, their compact size, lightweight design, and small footprint reduce costs for investors. Third, the simple structure, minimal vulnerable parts, and long maintenance intervals minimize operational and repair efforts. Furthermore, centrifugal pumps feature excellent adjustability and reliable operation. Notably, they require no internal lubrication, ensuring the purity of the transported fluid without contamination from lubricants.    c. Types of Losses and Efficiency Main hydraulic losses include vortex, resistance, and impact losses, with efficiency being the ratio of effective power to shaft power. Hydraulic losses in centrifugal pumps, also known as flow losses, refer to the difference between theoretical head and actual head. These losses occur due to friction and impact during liquid flow within the pump, converting part of the energy into heat or other forms of energy loss. Hydraulic losses in centrifugal pumps primarily consist of three components: vortex loss, resistance loss, and impact loss. These combined effects create the difference between theoretical and actual head. The efficiency of a centrifugal pump, also called mechanical efficiency, is the ratio of effective power to shaft power, reflecting the extent of energy loss during operation.   d. Speed and Power Speed affects flow rate and head, with power measured in watts or kilowatts. The speed of a centrifugal pump refers to the number of rotations the pump rotor completes per unit time, measured in revolutions per minute (r/min). The power of a centrifugal pump, or the energy transmitted to the pump shaft by the prime mover per unit time, is also known as shaft power, typically measured in watts (W) or kilowatts (KW).   e. Head and Flow Rate When speed changes, flow rate and head vary according to square or cubic relationships. Adjusting the speed of a centrifugal pump alters its head, flow rate, and shaft power. For unchanged media, the ratio of flow rate to speed exceeds the speed itself, while the ratio of head to speed equals the square of the speed ratio. Meanwhile, the ratio of shaft power to speed equals the cube of the speed ratio.   f. Number of Blades and Materials The number of blades typically ranges from 6 to 8, with materials requiring corrosion resistance and high strength. The number of blades in a centrifugal pump impeller is a critical parameter directly affecting pump performance. Generally, the blade count is set based on specific applications and needs, ensuring efficient and stable operation. Common manufacturing materials include gray cast iron, acid-resistant silicon iron, alkali-resistant aluminum cast iron, chromium stainless steel, etc.   g. Pump Casing and Structure The pump casing collects liquid and increases pressure, with common structures including horizontal split-type designs. The pump casing plays a vital role in centrifugal pumps. It not only collects liquid but also gradually reduces liquid velocity through specific channel designs. This process effectively converts part of the kinetic energy into static pressure, enhancing liquid pressure while minimizing energy loss due to oversized channels. Common pump casing structures include horizontal split-type, vertical split-type, inclined split-type, and barrel-type designs.   With the continuous updates in process technology for chemical enterprises, stricter demands are placed on the stable operation of chemical centrifugal pumps. These pumps play a crucial role in the chemical industry, where their performance stability directly impacts the smoothness of the entire production process. Therefore, a deep understanding and rational selection of pump casing support forms are essential for ensuring the stable operation of chemical centrifugal pumps.