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.

 

 

In the structure of a centrifugal pump, the mechanical seal is a core component, directly related to the stable operation and service life of the equipment. The primary function of the mechanical seal is to prevent fluid leakage from the pump, ensuring its normal operation and working efficiency. However, in practical applications, the mechanical seal of centrifugal pumps is often affected by factors such as operating conditions, medium characteristics, and operational maintenance, leading to failures. This results in seal damage, pump leakage, and even equipment shutdown, adversely impacting production safety and environmental protection. Failure of the centrifugal pump mechanical seal not only affects the equipment's performance and safety but also leads to high maintenance costs, increasing production expenses for oilfield enterprises. Therefore, researching the causes and damage mechanisms of mechanical seal failures in centrifugal pumps, and subsequently proposing effective prevention and improvement measures, is of significant importance for reducing the failure rate of mechanical seals and extending their service life. Anhui Shengshi Datang will give you an overview.

1. Analysis of Centrifugal Pump Operating Principle

The operation of a centrifugal pump is based on Bernoulli's equation in fluid dynamics, which states that within a closed system, the energy of a fluid comprises kinetic energy, potential energy, and pressure energy, and these three forms of energy are converted within the pump. The core components of a centrifugal pump are the impeller and the pump casing. When the electric motor drives the pump shaft to rotate, the impeller rotates at high speed, causing the liquid inside the pump to also undergo rotational motion. Under the action of centrifugal force, the liquid is thrown from the center of the impeller towards its periphery, gaining an increase in both kinetic and pressure energy. This change in kinetic and pressure energy causes the liquid to flow out through the pump casing outlet. The pressure at the center of the impeller decreases, forming a low-pressure area, and liquid is continuously drawn into the pump under atmospheric pressure, thus forming a continuous liquid transport process. The operation of a centrifugal pump can be divided into three stages: liquid suction, acceleration, and discharge. In the suction stage, due to the low-pressure zone formed at the impeller center, external liquid flows into the pump under atmospheric pressure. In the acceleration stage, the liquid, acted upon by centrifugal force through the impeller, accelerates towards the pump casing. In the discharge stage, the high-speed liquid is gradually decelerated through the diffuser or volute, converting kinetic energy into pressure energy before being discharged from the pump.

The main components of a centrifugal pump include the impeller, pump casing, pump shaft, mechanical seal, and bearings. The impeller, made of materials like cast iron, stainless steel, or plastic, is the core component. Its design directly determines the pump's flow rate and head. Parameters such as the impeller's shape, size, number of blades, and blade angle significantly affect liquid flow and pressure conversion efficiency. The pump casing, typically volute-shaped, contains the fluid. Its main functions are to collect liquid discharged from the impeller and guide it to the discharge outlet. The casing also facilitates energy conversion by gradually converting the liquid's kinetic energy into pressure energy through diffusion, thereby increasing the pump's head. The pump shaft, driven by the motor and connected to the impeller, transmits mechanical energy from the motor to the impeller, causing it to rotate. The pump shaft must possess high strength and stiffness to withstand centrifugal forces and the reaction forces of the liquid on the impeller. The mechanical seal prevents liquid leakage at the point where the pump shaft and casing interact. Its performance directly affects the pump's efficiency and safety. Bearings support and fix the pump shaft, reducing friction and vibration during rotation, ensuring stable pump operation.

2. Causes of Leakage in Centrifugal Pump Mechanical Seals

(1) Trial Run Leakage.​ The installation precision of the mechanical seal directly affects its sealing effectiveness. If the seal faces are not accurately aligned during installation or if the face gap is set improperly, leakage can occur during trial operation. The stationary and rotating rings should be flat and aligned during installation. Failure to meet this standard can result in poor contact between the sealing faces, creating gaps and allowing medium leakage. Similarly, improper tightening according to design requirements or vibration during installation can cause misalignment of the seal rings, compromising the seal. During the trial run phase, the seal faces may not be fully bedded-in. Under high-speed operation and friction, face wear can lead to leakage. This wear is common if the seal faces have not been pre-treated or run-in, as initial high surface roughness increases frictional heat, exacerbating wear. Face wear reduces the contact integrity of the sealing surfaces, leading to leakage. Additionally, excessively rapid temperature rise during trial runs can cause uneven thermal expansion of the faces, accelerating wear. Vibration generated during pump operation due to bearing wear, imbalance, or other mechanical issues can affect the mechanical seal, which is sensitive to vibration. Vibration causes uneven pressure distribution between the seal faces, potentially leading to misalignment of the rotating and stationary rings, seal failure, and leakage. Particularly during trial runs, excessive axial shaft movement or radial runout beyond standards can adversely affect the stability of the seal components.

(2) Static Test Leakage.​ In mechanical seals, auxiliary sealing elements are typically made of materials like rubber or PTFE. The elasticity and corrosion resistance of these materials significantly impact sealing performance. Improper material selection for auxiliary seals can lead to leakage during static pressure testing. If the seal material lacks corrosion resistance or temperature tolerance, it may deform under static test pressure or temperature, failing to provide an effective seal. Simultaneously, aging, hardening, or loss of elasticity due to temperature changes can prevent the seal faces from fitting tightly, causing leakage. During static testing, pressure within the seal chamber should not fluctuate significantly. Otherwise, uneven pressure on the seal faces may cause leakage. Static tests are usually conducted at slightly higher pressures than operating pressure to verify seal integrity. However, if the pressure is too high or applied unevenly, the seal components can be damaged, compromising the contact between the stationary and rotating rings and causing leakage. Especially during static tests, if the liquid temperature is high, thermal expansion within the seal chamber can cause pressure fluctuations, leading to inadequate sealing. The seal faces, often made of wear-resistant, high-strength materials like silicon carbide or ceramic, are critical. If subjected to excessive pressure during installation or static testing, minor deformation can occur, affecting the faces' ability to mate properly.

(3) Operational Leakage.​ The operating conditions of a centrifugal pump may change with its working state. Variations in fluid temperature, pressure, or flow rate can all affect seal performance. When operating conditions exceed the seal's design limits—such as excessively high temperature or pressure—the material properties of the seal components can degrade, leading to seal failure. Leakage is particularly likely during transient flow fluctuations or under highly variable load conditions. Mechanical seals often rely on the presence of a seal fluid for adequate lubrication and cooling. Insufficient seal fluid flow or excessively high temperature can cause the seal fluid to evaporate or vaporize, reducing sealing effectiveness. Furthermore, impurities or contaminants in the seal fluid can enter the seal chamber, impairing lubrication between the seal faces, accelerating wear, and causing leakage. The material selection and design of the mechanical seal are directly related to its performance. If the seal material has insufficient corrosion resistance, it may corrode when exposed to the pump fluid, leading to decreased sealing performance. Similarly, poor design can cause uneven force distribution on the seal faces or issues related to thermal expansion, resulting in seal failure. Therefore, appropriate material selection and sound design are crucial factors for ensuring the stability of the mechanical seal during normal operation.

(4) Cooling Water Quality.​ The role of cooling water is to ensure temperature control for the mechanical seal, preventing seal failure due to high temperatures. If the cooling water quality does not meet standards, it can lead to mechanical seal leakage. If the cooling water contains impurities, solid particles, oil contamination, or other pollutants, it can negatively impact the working environment of the mechanical seal. These impurities may enter the seal chamber, causing wear on the stationary and rotating rings, reducing the smoothness of the seal faces, and thus inducing leakage. Simultaneously, the presence of pollutants can obstruct the flow of cooling water, preventing it from effectively carrying away the heat generated at the seal faces, further exacerbating wear and temperature rise. The chemical composition of the cooling water can also affect the materials of the mechanical seal. Cooling water containing high concentrations of corrosive agents can accelerate the corrosion of seal materials, reducing their service life. If the materials used in the mechanical seal are not corrosion-resistant, prolonged exposure to such cooling water can lead to cracks, pitting, or spalling on the seal faces, ultimately causing leakage. The temperature of the cooling water is crucial for the performance of the mechanical seal. If the cooling water temperature is too high, it may cause softening or aging of the seal materials, reducing their elasticity and sealing effectiveness. As temperature increases, the seal components may not maintain the designed tight contact, leading to leakage.

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.

Welcome everyone to join Anhui Shengshi Datang in learning about submersible pumps.

 Common Faults of Submersible Pumps

1. Electric Leakage

Electric leakage is one of the most common and dangerous faults in submersible pumps, as it poses a serious threat to human safety. When the switch is turned on, the leakage protection device in the transformer distribution room may automatically trip. Without such protection, the motor could burn out. Water entering the pump body lowers the insulation resistance of the submersible pump. Long-term use can cause wear on the sealing surfaces, allowing water to seep in and create leakage.

Once leakage occurs, the motor should be removed and dried in an oven or with a 100–200 Ω lamp. Afterward, replace the mechanical seal, reassemble the pump, and then it can be safely operated again.

2. Oil Leakage

Oil leakage in a submersible pump is mainly caused by severe wear or poor sealing of the oil seal box. When oil leakage occurs, oil stains can often be seen near the water inlet. Remove the screws at the inlet and carefully inspect the oil chamber for water intrusion. If water is found inside, it indicates poor sealing and the oil seal box should be replaced immediately to prevent water from entering the oil chamber and damaging the motor.

If oil stains appear around the cable connection, the leakage is likely from inside the motor, possibly due to a cracked joint or substandard lead wire. After identifying the cause, replace the defective parts and check the motor’s insulation. If the insulation is compromised, replace the oil inside the motor with fresh oil.

3. Impeller Does Not Rotate After Power-On

If the pump emits an AC humming sound when powered on but the impeller does not rotate, cut off the power and try to manually rotate the impeller. If it does not move, it is jammed and the pump must be disassembled for inspection. If the impeller moves freely but still does not rotate when powered, the likely cause is worn bearings. The magnetic field generated by the stator may attract the rotor, preventing it from turning. When reassembling the pump, ensure the impeller rotates freely to eliminate this issue.

4. Low Water Output

After removing the rotor, check whether it rotates smoothly. When dismantling the pump, inspect for looseness between the lower part of the pump and the bearing. If the rotor has dropped, it means the rotor’s rotational force is reduced, resulting in decreased power output. Place an appropriate washer between the bearing and the rotor, reassemble the pump, and perform a test run to gradually identify and resolve the fault.

   Submersible Pump Maintenance

1. Correct Assembly and Disassembly Methods

Before disassembly, mark the joint between the end cover and the base to ensure proper alignment during reassembly and avoid shaft misalignment. After removing the impeller, use the heat expansion and cold contraction method — heating and lightly tapping to detach it. During disassembly, carefully inspect the winding for damage and analyze the cause. When removing damaged windings, protect the iron core and plastic insulating rings to prevent damage to insulation or electromagnetic components. Always use proper tools and techniques to avoid harming other parts. 

2. Analysis of Winding Burnout Causes

During motor disassembly, avoid moving the assembly excessively to prevent grounding or short circuits when installing new windings. When rewinding, always use wires from reliable manufacturers to ensure quality. For low-insulation areas, use insulation materials of sufficient thickness and ensure padding is properly installed. Do not use sharp tools to scrape the wires during winding, as this may damage insulation.

3. Proper Waterproof Insulation of Cable Joints

At the joint, remove the sheath and insulation layer, and clean any oxidation from the copper wire surface. Wrap the connection securely with polyester adhesive tape to form a mechanical protective layer and ensure waterproof insulation. 

4. Preparations Before Powering On

Before energizing the motor, fill it with clean water to help cool the windings and provide lubrication. Operating the motor without water can cause severe damage. In winter, be sure to drain the water from the motor to prevent freezing and cracking.

5. Correct Application of Insulating Varnish to Motor Coils

After forming the stator, immerse it completely in insulating varnish for about 30 minutes before removing it. Then brush varnish evenly on the surface. Since varnish has high viscosity and poor penetration, brushing alone may not provide a uniform coating or meet required insulation quality standards.

   Proper Maintenance Practices

Proper maintenance is crucial for extending the service life and efficiency of submersible pumps. If the pump will not be used for an extended period, it should be removed from the well and all components should be inspected to prevent rusting. For pumps with long service history, disassemble and clean all internal parts, including removing screws and flushing sediment from the impeller. Severely worn components should be replaced promptly.

If rust is found, clean the affected areas, apply oil, and reassemble. Always check the sealing parts. Store electric pumps in a dry, well-ventilated place to prevent moisture damage. Add lubricating oil periodically, using low-viscosity, water-insoluble oil.

 

Avoid long-term overload operation or pumping water containing large amounts of sediment. When the pump runs dry, limit the duration to prevent motor overheating and burnout. During operation, the operator should continuously monitor the working voltage and water flow. If either exceeds the specified range, the motor should be stopped immediately to prevent damage.

 

The horizontal multistage centrifugal pump is a type of fluid machinery primarily used for liquid transportation. It features high delivery efficiency and can be applied to the transfer of crude oil and chemical products, intermediate process liquids, cooling and circulation systems, as well as waste treatment and discharge. A petrochemical plant typically operates thousands of horizontal multistage centrifugal pumps. Prolonged operation inevitably leads to wear and technical failures, which can reduce operating efficiency and increase both production costs and the risk of shutdowns for maintenance. Currently, the petroleum industry generally adopts the DG-2499Y horizontal multistage centrifugal pump. Anhui Shengshi Datang will conduct an in-depth analysis of its technical parameters, explore possible causes of technical failure, and propose targeted maintenance recommendations to provide a systematic repair plan, ensuring equipment stability and continuous plant operation.

   Technical Parameters

The horizontal multistage centrifugal pump consists of multiple pump stages connected in series, with each stage including an impeller and a corresponding diffuser. In each stage, the liquid gains kinetic energy through the impeller, which is then partially converted into pressure energy in the diffuser—thus progressively increasing the total output pressure of the pump.

This pump features a compact structure, ease of maintenance, and high efficiency in handling large flow rates, meeting high head requirements. Its rated flow ranges from 6 to 1000 m³/h, with a rated head between 40 and 2000 m. Operating speeds include 3500 r/min, 2900 r/min, 1750 r/min, and 1450 r/min, with a working frequency of 50 Hz or 60 Hz.

Taking the DG-2499Y horizontal multistage centrifugal pump as an example, its key technical features include:

 a. Two bearings installed on the front and rear shafts.

 b. The pump and motor are connected by an elastic pin coupling, with the motor rotating clockwise during operation.

 c. The suction inlet is set horizontally, while the discharge outlet is vertical.

 d. Bearings are lubricated with grease, and the shaft seal can be either a packing seal or a mechanical seal.

   Failure Cause Analysis

A. Dry Running Without Lubrication

Dry running occurs when the pump operates without sufficient lubrication due to failure or absence of lubricant. For the DG-2499Y pump, the bearings and shaft sleeves rely on lubrication to minimize friction and wear. Without lubrication, these parts can quickly wear out due to high friction and heat. The packing seal’s effectiveness may also decrease, leading to shaft seal failure and leakage. Excessive bearing wear can cause instability, resulting in impeller imbalance, increased vibration and noise, and reduced efficiency and lifespan. In extreme cases, complete bearing failure may occur, causing severe mechanical damage and shutdown.

B. Chemical Corrosion

In petrochemical applications, the DG-2499Y pump often handles chemically aggressive media such as crude oil, intermediate refinery products, and other chemical process fluids. These media may contain corrosive compounds such as sulfides, acids, and alkalis, which can attack metal components like impellers, shafts, and sleeves. Prolonged exposure leads to structural weakening, cracking, or pitting corrosion. Factors such as temperature, concentration, and flow velocity significantly affect corrosion rate. For instance, high temperatures accelerate corrosion, while high velocities can cause erosion–corrosion, where chemical attack and mechanical wear act simultaneously. Chemical reactions may also deteriorate packing and seal materials, reducing sealing performance and causing leakage or pump failure.

C. Overheating During Operation

During long-term operation, friction, poor heat dissipation, or high process fluid temperature may lead to overheating. Bearing overheating is common, often caused by insufficient or poor-quality lubricant. Under high-speed rotation, frictional heat between shaft sleeves can degrade material properties. Impellers and sealing rings may lose mechanical strength at elevated temperatures, reducing pump efficiency or causing structural damage. Insufficient flow in the recirculation or discharge lines can also lead to overheating, resulting in component fatigue, accelerated wear, and reduced service life.

D. Solid Particle Contamination

In petrochemical operations, pumps may be damaged by solid impurities in the conveyed medium—such as unreacted catalyst particles, sediments, corrosion products, or small debris. When these enter the pump, especially through the suction section and impeller, they increase wear on these components and reduce efficiency. Continuous particle erosion can severely wear sealing rings, shafts, and sleeves, leading to seal failure and performance degradation.

E. Cavitation

Cavitation occurs when the pressure at the suction side drops to or below the liquid’s vapor pressure, forming vapor bubbles that collapse in high-pressure regions. The resulting shock waves damage impellers and internal components. This phenomenon is common in petrochemical applications where volatile solvents or gases are present, especially under high-temperature or low-pressure conditions.

   Key Maintenance Techniques

A. Zero-Flow Issue After Startup

 a. When a DG-2499Y pump exhibits zero flow after startup, technicians should perform precise diagnostics:

 b. Use pressure testing instruments to verify system sealing, ensuring no gas or liquid leakage, especially at the shaft seal and packing areas. 

 c. Monitor flow and pressure readings to identify internal blockages or piping faults. 

 d. Check motor-pump alignment to ensure efficient power transmission through the coupling.

 e. Use infrared thermography to detect heat concentration indicating friction hotspots.

 f. Replace or repair faulty components (e.g., impellers, bearings) and realign using laser tools.

 g. Ensure all maintenance steps meet petrochemical safety and technical standards for stable operation.

B. Flow Rate Troubleshooting

 a. Flow issues often result from chemical corrosion, solid contamination, or cavitation. Maintenance should include:

 b. Evaluating the pump’s Q–H (flow–head) curve to determine deviations.

 c. Cleaning or replacing worn or fouled impellers.

 d. Inspecting and replacing worn sealing rings and bearings.

 e. Measuring actual vs. theoretical flow using flowmeters and adjusting inlet valves as needed.

 f. Checking for cavitation and optimizing NPSH (Net Positive Suction Head) conditions to prevent vapor ingestion.

 g. Detecting blockages or leaks in the pipeline with ultrasonic flow and pressure sensors and repairing as required.

C. Overload in the Drive System

 a. To resolve motor or drive overload:

 b. Conduct full performance tests using instruments like clamp ammeters and power analyzers to ensure operation within rated limits.

 c. Inspect impellers, bearings, and seals for wear or damage that may increase load.

 d. Remove internal blockages and ensure smooth fluid flow.

 e. Precisely align the pump and motor to reduce mechanical transmission losses.

D. Bearing Overheating

 a. Maintenance steps include:

 b. Using vibration analyzers to detect abnormal bearing vibration—an early sign of overheating.

 c. Regularly monitoring bearing temperature via infrared thermography; disassemble and replace damaged bearings when necessary.

 d. Inspecting and cleaning the lubrication and cooling systems to ensure proper lubricant flow and quality.

 e. Verifying correct bearing installation and alignment to minimize frictional heat.

E. Vibration Troubleshooting

 a. Pump vibration may result from impeller blockage or imbalance, misalignment, or loose components. Maintenance personnel should:

 b. Use vibration and laser alignment tools to diagnose misalignment.

 c. Adjust bearing preload to prevent overheating and vibration.

 d. Inspect impellers for damage or imbalance and perform dynamic balancing if necessary.

 e. Tighten all fasteners, including shaft sleeve nuts and bolts, to ensure structural stability and safe operation.

In industries such as chemicals, pharmaceuticals, and new materials, the tank farm area serves as a critical transfer point connecting raw material supply with workshop processes. Especially for long-distance liquid transfer from storage tanks to workshops, ensuring safety, sealing performance, and stable conveying becomes the core of equipment selection. Magnetic pumps, with their leak-free and explosion-proof structure, have become the preferred solution for transferring raw materials and finished products in tank farm systems.

1. Transfer Scenario: Challenges from the “Tank Area” to the Workshop

A “tank area” refers to the zone for raw material unloading, product loading, and intermediate material storage. In actual operations, liquids are transferred from tank trucks into storage tanks, typically within a distance of around 20 meters. Next, the material must be conveyed stably through pipelines to workshops located more than 50 meters away.

This type of transfer scenario has three typical characteristics:

A. Long distance and high head requirements: Pipeline lengths often exceed 50 meters; head must account for pipeline resistance and elevation differences.

B. Media are usually volatile or toxic: Such as alcohols, ketones, and organic solvents—requiring excellent system sealing.

C. High explosion-proof requirements and limited maintenance access: Usually located in hazardous areas, demanding reliable, low-maintenance equipment.

2. Why Magnetic Pumps Are Suitable for Tank Area Transfer

Shengshi Datang magnetic pumps use magnetic coupling drive and require no mechanical seals, eliminating leakage risks structurally. For toxic, flammable, or volatile media, magnetic pumps offer true zero-leakage performance.

Through optimized flow channels and efficient magnetic drive systems, Shengshi Datang magnetic pumps ensure stable output even during long-distance transfer, making them especially suitable for high-frequency transfers from tank farms to workshops.

3. Key Points for Pump Selection

A. Head Matching: For pipelines exceeding 50 meters, account for frictional and local resistance, as well as tank liquid level and workshop elevation. It is recommended to design the pump head at 1.2× the actual requirement as a safety margin.

B. Material Selection: Wetted parts should be selected according to the medium’s corrosiveness—stainless steel, fluoroplastic lining, or other corrosion-resistant materials.

C. Flow Rate Determination: Select based on unloading or process requirements, generally using the maximum required flow to avoid insufficient feeding or frequent start–stop cycles.

D. Motor Configuration: Use explosion-proof motors, with a grade not lower than EX d IIB T4, matching the operating conditions to ensure long-term safe operation.

E. Cooling Structure: For easily vaporized liquids, choose magnetic pumps with auxiliary cooling circuits to prevent demagnetization of the inner magnet or local cavitation in the pump chamber.

4. Reference Case

At a fine chemical plant in East China, ethanol is transferred from the tank area to a workshop around 55 meters away. Initially, mechanical-seal centrifugal pumps were used, but frequent leakage and long maintenance cycles caused issues. They were later replaced with fluoroplastic-lined magnetic pumps equipped with explosion-proof motors and auxiliary cooling loops. After three years of operation, no leakage occurred, and maintenance costs dropped by more than 40%.

Long-distance transfer from tank areas to workshops demands high levels of stability and sealing from pumps. Magnetic pumps, with their sealless design and strong corrosion resistance, demonstrate significant advantages in such systems. During selection, factors such as transfer distance, medium characteristics, and site explosion-proof requirements should be thoroughly evaluated. Choosing products from manufacturers with extensive industry experience ensures long-term stable operation. Shengshi Datang Pump Industry’s magnetic pumps have been widely used in such applications and are a reliable choice.

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.

 

Centrifugal pumps are critical equipment in the oilfield gathering and transportation process. The mechanical seal is a vital component of the centrifugal pump, used to prevent medium leakage. Failure of the mechanical seal directly affects the stable operation of the equipment, leading to downtime for repairs, which impacts the gathering and transportation schedule and the economic benefits of the enterprise. Regarding the issue of mechanical seal failure and damage in centrifugal pumps, Anhui Shengshi Datang analyzes it based on the operating principles of centrifugal pumps and derives the following preventive measures.

1. Implement Proper Seal Assembly

Before assembling the mechanical seal, thorough preparations are essential. This includes inspecting the integrity and cleanliness of all assembly parts. Sealing components should be stored in a dust-free, dry environment to avoid contamination by dust and impurities. Simultaneously, necessary tools and materials should be prepared according to the technical specifications of the equipment manufacturer to ensure a smooth assembly process.

The installation of the mechanical seal must strictly follow the installation manual and standards provided by the manufacturer. Before assembly, carefully read the relevant technical documentation to understand the seal's structure and working principle, and clarify the installation sequence and methods for each component. Any operation not performed according to the specified procedures may lead to seal failure.

During the assembly of the mechanical seal, ensuring the alignment and concentricity of the stationary and rotating rings is crucial. Incorrect alignment can cause uneven contact on the sealing faces, leading to leakage. Special alignment tools can be used to ensure the seal components are on the same axis. Simultaneously, during assembly, check the pump shaft's diameter and concentricity to avoid wear caused by misalignment.

When assembling the mechanical seal, it is essential to apply uniform installation pressure. Use specialized tools to apply torque gradually according to the manufacturer's recommended values, ensuring fasteners are evenly stressed. Excessive or insufficient pressure can lead to poor contact of the sealing faces, increasing wear risk and causing leakage.

After completing the assembly, dynamic testing should be performed to verify the effectiveness of the mechanical seal. Through trial operation, observe for any leakage phenomena. During the testing process, operational parameters should be recorded to promptly identify and address potential issues.

2. Focus on Maintenance Management

Regular inspection of the mechanical seal is the foundation for ensuring its normal operation. A detailed inspection plan should be established to conduct comprehensive checks on the mechanical seal periodically. Observe the flatness and smoothness of the sealing faces, and check for cracks, scratches, or other damage. Ensure the spring has good elasticity without deformation or fracture. Inspect the wear condition of the seal seat, pump shaft, and other related components to ensure their proper functioning.

Cooling water is key to the normal operation of the mechanical seal, and its quality directly affects the seal's performance. Regularly test the chemical composition of the cooling water to ensure it is free from corrosive substances and solid impurities. Simultaneously, maintain the flow rate and temperature of the cooling water within appropriate ranges to effectively reduce the operating temperature of the sealing faces and prevent seal failure due to overheating.

During the operation of the mechanical seal, proper lubrication is crucial for maintaining normal contact between the sealing faces. Regularly check and replace the lubricant according to the manufacturer's recommendations. The selection of lubricant should comply with the characteristics of the seal materials. Avoid using lubricants incompatible with the seal materials to prevent adverse effects on seal performance.

Even under normal operating conditions, mechanical seals will eventually lose their sealing performance due to long-term wear. Therefore, a reasonable replacement cycle should be established to regularly replace severely worn seals, ensuring the normal operation of the equipment. When replacing seals, strictly follow the installation specifications to ensure the performance of the new seal meets requirements.

3. Enhance Maintenance Efforts

Establishing a scientific and reasonable maintenance plan is the foundation for enhancing maintenance efforts. Based on the usage conditions, working environment, and historical failure records of the centrifugal pump, define the maintenance cycle, content, and personnel. Regular preventive maintenance can effectively prevent minor faults from escalating into major problems, ensuring the normal operation of the mechanical seal.

After each maintenance, detailed maintenance records should be kept, including the maintenance date, content, issues found, actions taken, and parts replaced. These records not only provide a basis for subsequent maintenance but also help analyze the causes of failures and improve maintenance quality.

Real-time monitoring of the operating parameters of the centrifugal pump allows for the timely detection of abnormalities. Using an online monitoring system can promptly issue alarms when seal abnormalities occur, preventing further escalation of faults. Through data analysis, factors affecting the performance of the mechanical seal can be identified, enabling the formulation of corresponding improvement measures.

4. Strengthen Personnel Management

Defining the responsibilities of each position is the foundation of strengthening personnel management. Clear job description documents should be developed based on the operational and maintenance needs of the centrifugal pump. Each employee's work content, scope of responsibility, and assessment criteria should be clearly defined to ensure that all tasks during equipment maintenance and fault handling are assigned to specific individuals, forming a clear chain of responsibility.

Conduct regular training sessions focused on centrifugal pumps and mechanical seals to enhance employees' professional skills and fault-handling capabilities. Training content should cover the structure, working principles, common failures and their handling methods, maintenance, and inspection procedures of mechanical seals. By disseminating professional knowledge, employees' awareness of the importance of mechanical seals is enhanced, improving the standardization and safety of their operations.

Establish a scientific assessment mechanism to regularly evaluate employees' work performance. Assessment content should include technical proficiency, work attitude, fault-handling ability, and teamwork spirit. Through assessment, employees can be motivated to actively participate in the maintenance and management of mechanical seals, thereby improving overall work efficiency and quality.

Welcome to purchase magnetic pumps and centrifugal pumps.

 

 

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.

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.