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I. Knowledge on Equipment Failures 1. Meaning of failure: A failure occurs when a device loses or reduces its specified functions during operation and is no longer able to function. 2. Types of faults: Faults can be classified from different perspectives: 1) Temporary faults 2) Permanent faults. Based on the timing of occurrence, they can be categorized as follows: 1) Early-onset faults 2) Sudden faults 3) Progressive faults 4) Composite faults. According to their manifestation, they include: 1) Functional faults 2) Hidden faults. Based on the causes of the faults, we have: 1) Human-induced faults 2) Natural faults. Depending on the consequences caused by the faults, they can be classified as: 1) Fatal faults 2) Severe faults 3) Moderate faults 4) Minor faults. Usually, several classification methods are used in combination to describe faults, such as sudden local faults ； Wear-related critical failures, etc., reveal the complexity, severity, and causes of such failures. 3. Characteristics of failures: 1) Diversity 2) Hierarchy 3) Multiple factors and correlations 4) Delay 5) Uncertainty 6) Repairability. 4. Failure management: Failure management is one of the core aspects of equipment management. Its purpose is to detect signs of failure early and take timely measures for prevention and repair. The procedures and contents of fault management include: 1) a combination of publicity and education with technical training. 2) Establish strict management and maintenance systems. 3) Be familiar with the structure and working principles of mechanical equipment, and understand their performance characteristics. 4) Install advanced inspection, testing, and monitoring equipment to carry out real-time monitoring of critical equipment and components, conduct regular analyses, and accurately grasp information and signs of equipment failures. 5) Conduct a thorough and scientific analysis based on the fault symptoms, information, and signs, to determine the cause and type of the fault, select the optimal repair strategy and plan, and keep records of the repair process in a timely manner. Provide subsequent statistics and references. 6) Areas or components where failures occur frequently or repeatedly should be monitored closely, and systematic technical modifications should be carried out if necessary. Main factors affecting the occurrence of failures: 1) Impact of manufacturing and repair factors on failures: a) Selection of component materials; b) Quality of component processing; c) Quality of assembly. 2) Impact of usage factors on failures: a) Working load; b) Working environment; c) Equipment maintenance and operating skills. II. 11 indicators for equipment management: In enterprises, there are many indicators used to measure the quality of equipment management. For example, the equipment integrity rate, equipment availability rate, overall equipment efficiency, fully effective production rate of the equipment, equipment failure rate, average time between failures, average repair time, inventory turnover rate for equipment spare parts, capital expenditure on spare parts, cost ratio for repairs, first-pass quality rate for maintenance work, and rework rate, among others. Different indicators are used to measure different management aspects. Evaluation of management indicators: 1. Equipment integrity rate – This is the most commonly used indicator, but its role in facilitating management is limited. The so-called availability rate refers to the ratio of functional equipment to the total number of devices during inspection periods (Availability Rate = Number of functional devices/Total number of devices). Many factories manage to achieve an availability rate of over 95%. The reason is simple: at the time of inspection, if the equipment is running and not malfunctioning, it is considered to be in good condition, so this indicator shows a good value. If it looks good, that means there isn’t much room for improvement; it means nothing can be improved any further, and it also means it’s difficult to make progress. To this end, many companies have proposed modifying the definition of this indicator; for example, they suggest conducting checks on the 8th, 18th, and 28th of each month, and using the average of the good rate values obtained from these checks as the good rate for that month. This is of course better than checking once, but it still represents a good rate on a point-by-point basis. Later, it was proposed to use the ratio of available machine hours to calendar working hours, with the available machine hours equaling the calendar working hours minus the total hours spent on failures and their repairs. This indicator needs to be as accurate as possible. Of course, there are again issues related to the increased workload in statistics and the accuracy of those statistics, as well as debates over whether to deduct costs when it comes to preventive maintenance. Whether the integrity rate is an effective indicator of equipment management depends on how it is applied; different people may have different opinions on this. 2. Equipment failure rate: This metric is easy to confuse, as there are two definitions for it. First, if it refers to the frequency of failures, it is the ratio of the number of failures to the actual number of times the equipment was in operation (Failure frequency = Number of failures due to downtime / Actual number of operating hours of the equipment) ； Second, if it is the failure downtime rate, it is the ratio of the time the equipment is down due to failures to the sum of the time the equipment is actually in operation and the time it is down due to failures (Failure downtime rate = Time down due to failures / (Time actually in operation + Time down due to failures)). Clearly, the failure downtime rate can more accurately reflect the condition of the equipment. 3. Equipment availability is more commonly used in the West; in China, there are two different terms: planned time availability (planned time availability = actual working time/planned working time) and calendar time availability (calendar time availability = actual working time/calendar time). By definition, the availability rate as defined in the West is actually the calendar time utilization rate. Calendar time utilization reflects the full utilization level of the equipment; in other words, even for equipment that operates on a single shift basis, we calculate the calendar time based on 24 hours. Because whether the factory uses this equipment or not, it still consumes the company’s assets in the form of depreciation. The planned time utilization rate reflects the planned usage level of the equipment; in the case of single-shift operation, the planned time is 8 hours. 4. Another term for the average time between failures of a device, MTBF, is average time without failure (MTBF = total time the device operates without failure during the statistical period / number of failures). It reflects the frequency of failures, that is, the health status of the equipment, in a complementary manner to the failure downtime rate. It is sufficient to use one of the two indicators; there is no need to measure something using related indicators. Another indicator reflecting maintenance efficiency is the Mean Time To Repair (MTTR) (Mean Time To Repair = Total time spent on repairs during a statistical period / Number of repairs), which measures the improvement in the efficiency of maintenance work. With the advancement of equipment technology, due to differences in complexity, difficulty of maintenance, locations of failures, the average technical skill level of maintenance technicians, and the age of the equipment, it is difficult to determine a fixed value for maintenance time. However, we can use this to measure its average conditions and levels of improvement. 5. Overall Equipment Effectiveness, or OEE, is an indicator that provides a comprehensive reflection of equipment efficiency; it is the product of availability, performance, and quality factors. Just like a person, the time utilization rate represents the attendance rate; the performance utilization rate indicates whether one works hard after starting work and achieves the desired efficiency; the quality rate reflects the effectiveness of the work, showing whether mistakes are made frequently and whether tasks can be completed with both quality and quantity met. The simple formula for OEE is: Overall Equipment Effectiveness OEE = Output of qualified products / Theoretical output for the planned working time. 6. Total Effective Productivity, TEEP, is the formula that best reflects equipment efficiency rather than OEE. True Effective Productivity TEEP = Output of qualified products / Theoretical output over calendar time; this indicator reflects various deficiencies in the systematic management of equipment, including upstream and downstream impacts, effects of market and order conditions, imbalances in equipment capacity, and unreasonable planning and scheduling. This indicator is usually very low, which doesn’t look good, but it is highly accurate. Regarding maintenance and its management, there are also relevant indicators. 7. The first-time pass rate for maintenance quality is measured as the ratio of the number of times the equipment, after maintenance, meets the product quality standards upon its first trial run to the total number of maintenance sessions carried out. It is worth examining whether the factory uses this indicator as a performance metric for the maintenance team. 8. Rework rate: The total number of times equipment needs to be reworked after maintenance, divided by the total number of maintenance sessions. This more accurately reflects the quality of maintenance. 9. Maintenance cost ratio: There are various definitions and calculation methods for this ratio. One is the ratio of annual maintenance costs to the total annual output value; another is the ratio of annual maintenance costs to the total original value of assets during that year; yet another is the ratio of annual maintenance costs to the total replacement cost of assets in that year; there is also the ratio of annual maintenance costs to the total net value of assets in that year; and finally, it can be the ratio of annual maintenance costs to the total production costs for that year. The author believes that the last algorithm is more reliable. Even so, the magnitude of this repair cost rate figure does not tell us anything. Because equipment maintenance is a form of investment, and investment creates value and output. Insufficient investment and significant production losses affect output ； Of course, excessive investment is also not ideal; it is known as over-maintenance and constitutes a waste. Appropriate investment is ideal. Therefore, factories should explore and determine the optimal ratio of inputs. High production costs mean more orders and a greater workload, which in turn increases the load on the equipment and raises the need for maintenance. Making investments in the right proportions should be the goal that factories strive to achieve. With this benchmark in place, the further one deviates from this indicator, the less ideal it is. There are also many indicators related to spare parts management. 10. The spare parts inventory turnover rate (Spare parts inventory turnover rate = Monthly cost of spare parts used / Average monthly value of spare parts inventory) is a relatively representative indicator. It reflects the liquidity of spare parts. If a large amount of capital is tied up in inventory, it will be reflected in the turnover rate. Another indicator reflecting spare parts management is the spare parts capital ratio, which is the ratio of the total funds allocated to spare parts to the total original value of the company’s equipment. This value varies depending on whether the factory is located in a central city, whether the equipment is imported, and the extent of the losses caused by equipment downtime. If the daily downtime cost of a device amounts to tens of millions of yuan, or if the failure poses serious threats to environmental pollution and human safety, and if the lead time for obtaining spare parts is long, then a higher level of spare parts inventory is necessary; otherwise, the capital investment associated with spare parts should be kept as low as possible. 11. Intensity of maintenance training (Intensity of maintenance training = Hours spent on training / Total hours spent on maintenance work). Training includes knowledge of the device’s structure, maintenance techniques, professional ethics, and maintenance management. This indicator reflects the degree of emphasis and investment companies place on improving the competence of their maintenance staff, and it also indirectly reflects the level of their maintenance technical skills. It is very helpful for factory managers to be aware of these key performance indicators, as they assist in evaluating and driving progress in equipment management. Some factories feel upset when they see the maintenance workers often idle, drinking tea, smoking, and resting. The idea was to evaluate maintenance staff based on the amount of work they do, but it had the opposite effect. The equipment repaired by maintenance staff always leaves residual issues and complications, with new repair tasks constantly arising. The maintenance staff end up being as \"busy\" as firefighters, and the condition of the equipment actually worsens, leading to greater production losses due to downtime. How to evaluate the performance of maintenance organizations becomes another complex and worthy of study issue. The system is like a ball: if one side is flattened, it bulges out on the other side. The design of KPIs for equipment management is also related to the smooth operation of a company. III. Seven common misconceptions about equipment management Equipment management is the material foundation that ensures a company’s ability to produce and reproduce, and it is also the basis of modern production. Due to the long-term influence of traditional maintenance models and a reactive approach to maintenance, there are currently seven common misconceptions in the equipment management practices of domestic enterprises, which severely hinder the improvement of their equipment management capabilities and the process of modernization. To meet the requirements of modern equipment management models, equipment managers must move beyond misconceptions and establish a new framework of understanding. Myth 1: All equipment will fail. Correction: The reliability-centered maintenance approach shows that, by relying on reliability data analysis and utilizing advanced testing techniques and diagnostic methods, it is possible to achieve zero equipment failures. This approach gives maintenance work a greater degree of focus, aligns the subjective and objective aspects better, enhances its scientific nature, and reduces arbitrary actions. Myth 2: Equipment must undergo regular major repairs. Correction: Research in recent years has shown that with the use of new materials and new manufacturing processes, the reliability of equipment is increasing, while its intangible wear and tear is accelerating. For over 60% of the equipment, the failure rate curve shows only an initial failure period, with no wear-related failure period. Blind overhauls will introduce a new initial failure period, increasing the equipment failure rate. Due to the different movements of various components of the equipment, as well as differences in load and operating environment, wear and degradation as well as damage vary. Therefore, local repairs, such as minor repairs, component repairs, or repairs of assemblies, are more economical and reasonable. Myth 3: It’s difficult to find the cause of a fault when there are no problems. Correction: Faults don’t appear out of nowhere; they develop over time. Problems such as dust, oil contamination, stress, microcracks, corrosion, loosening, poor contact, and aging are all causes of failures. Therefore, there are numerous underlying problems associated with the malfunction that we need to carefully observe and identify; this is also the purpose of team-based maintenance. By strengthening the foundation and starting with the small details such as inspection, cleaning, maintenance, corrosion prevention, vibration reduction, and balancing, it is possible to prevent problems before they occur; this is also the most cost-effective strategy for equipment maintenance. Myth 4: It’s difficult to manage spare parts effectively while balancing the need for repairs with the goal of reducing spare parts inventory. Correction: By properly categorizing spare parts, storing critical ones in excess quantities, keeping ordinary spare parts at normal levels, allowing a shortage of less important spare parts, and eliminating inventory for many other spare parts, it is possible to reduce inventory costs without facing emergencies due to shortages. For example, equipment, components, and parts are classified into A, B, and C categories based on their level of importance, ranging from AAA to CCC. Depending on this level of importance, a management system is implemented that involves maintaining redundant inventory, regular inventory, inventory that can be depleted, or even no inventory at all – in which only information is kept rather than the actual parts. Myth 5: It’s impossible to involve operators in equipment maintenance. Correction: Operators come into contact with the equipment daily and know best its various capabilities ； Abnormalities in the sound, temperature, movements, odors, color, etc., of the equipment during operation are also the first things that on-site operators notice. Therefore, whether the operator can perform the tasks correctly and is responsible for the equipment makes a big difference in the outcome. As equipment becomes more automated, operations become simpler and easier, which also makes it possible for operators to take on more responsibility for the equipment. Myth 6: The organizational structure for equipment management in enterprises cannot be changed. Correction: Equipment management organizations should strive to become more flat, with better professional coordination, process prioritization, streamlined management processes, reduced division of labor, and blurred boundaries between different responsibilities. The reason is: too many layers create more problems, solve fewer problems, lengthen the management cycle, and reduce efficiency ； The production site is like a battlefield; following the principle of prioritizing tasks, those at the same level can give orders to one another, enabling streamlined management and rapid responses ； Implementing a less rigid division of labor and blurring boundaries can turn shirking responsibilities into proactive support ； Always adhere to establishing positions based on needs and assigning people to those positions accordingly. Myth 7: Companies need a maintenance team capable of handling all equipment issues. Correction: The conflict between advanced equipment and inadequate maintenance teams will always exist. Socialized maintenance is the trend of the future, and what companies need to do is focus on integrating maintenance resources and improving maintenance management. IV. Six Basic Characteristics of Equipment Management 1. Productivity The productivity of equipment for enterprises is self-evident. Therefore, preventive measures and maintenance should be carried out for key equipment ； For ordinary equipment, maintenance can be carried out after the fact, with the focus on how to reduce the equipment failure rate. As long as maintenance and production are closely integrated, smooth production can be ensured to the greatest extent. 2. Comprehensiveness: By comprehensiveness is meant the management of equipment throughout its entire life cycle. That is, it manages the entire lifecycle of equipment, covering all stages such as planning, design, manufacturing, installation, operation, maintenance, and disposal of the equipment. 3. Cost efficiency: The purchase of equipment represents an economic expense in itself, and the maintenance costs incurred during the equipment’s operation are also significant financial burdens for businesses. Additionally, the losses resulting from equipment downtime are expenses that companies must bear as well. Therefore, from an economic perspective, team leaders must strike a balance between the costs associated with equipment downtime and the expenses required for repairs. 4. Systematicity: In modern equipment management for production maintenance, a comprehensive system approach has been established that integrates preventive maintenance, corrective maintenance, and maintenance prevention. In other words, team leaders can use systematic management to improve the feedback on maintenance prevention, thereby enhancing the reliability and maintainability of equipment. 5. Participation by all employees: Equipment management is not the responsibility of just one person; it requires the involvement of all employees. Many companies adopt the approach of applying theories from behavioral science to boost the enthusiasm for equipment management among all employees, from managers down to staff, and to establish a sound system of self-management in order to facilitate the smooth implementation of equipment management. 6. Scientificity: From a scientific perspective, equipment management has gradually emerged on the basis of the development of various scientific theories. In other words, equipment management applies many theories from modern management science, making its management methods more scientific. V. Key Points for the Maintenance of Centrifugal Pumps and Analysis of Reasons for Motor Burnout 1. Key Points for the Maintenance of Centrifugal Pumps 1) Minor maintenance tasks 01 Replace the packing seal. 02 Double-support pump: Inspect and clean the bearings, bearing housings, oil shields, water shields, oil level gauges, etc., and adjust the bearing clearance. 03 Check and repair the alignment of the coupling as well as that of the drive unit and the pump. 04 Handle common defects that occur during operation. 05 Inspect and clean the cooling water, seal oil, lubrication, and other systems. 2) Major repair project 01 includes minor repair projects. 02 Check and repair the mechanical seal. 03 Inspect each component for wear, corrosion, and erosion during disassembly. Non-destructive testing is performed on the pump shaft and impeller when necessary. 04 Inspect and clean bearings, oil seals, etc., and measure and adjust the clearance of bearing oil seals. 05 Check the circular runout and clearances of various parts of the rotor, and perform dynamic balancing testing if necessary. 06 Check and correct the straightness of the shaft. 07 Measure and adjust the axial play of the rotor. 08 Check for any misalignment in the pump body, foundation, foot bolts, and inlet/outlet flanges, to prevent additional stress from being applied to the pump body; reconfigure the piping if necessary. When disassembling and maintaining a centrifugal pump, the three stages of disassembly, maintenance, and reassembly must be carried out in accordance with the specified requirements and procedures. 3) During disassembly, 01: Before removing the thrust bearing, use a dial indicator to measure the clearance of the balance disk and record the value ； 02 When disassembling a multi-stage pump, it is necessary to mark each component in its original assembly order to avoid confusion and incorrect installation during reassembly ； 03 Small items that are difficult to mark (such as keys) can be placed together with impellers or guide vanes of the same level (in the middle section), etc ； 04 When disassembling, it is possible to visually check for any abnormal parts, such as loose fits. 4) During maintenance, visually inspect part 01 to ensure that the surfaces of all components are in good condition; there should be no dents, scratches, or rust on any of the mating surfaces ； 02 Use measuring tools to actually check whether the tolerances of the key mating parts are within acceptable limits ； 03 Check whether the clearances at the impeller seal rings, casing seal rings, guide vane seal rings, inter-stage shaft sleeves, etc., are within the allowable range; those that are excessively worn need to be replaced ； 04 Check whether the bearing is in good condition ； 05 It is best to replace all seals and gaskets with new ones. 5) During reinstallation, 01 should first install the rotor and then conduct a dynamic balance test again ； 02 Reinstall all components in the reverse order of disassembly. When reinstalling, be sure to measure the clearance at each seal ring again to ensure accuracy ； 03 The total rotor string length should be measured before installing the balance disc ； 04 After installing the balance disk, measure the rotor’s half-string length ； 05 When compared with the total string length and half-string length specified in the manufacturer’s general assembly diagram, it should generally meet the requirements of the drawings. Under normal circumstances, the half-string quantity is roughly half of the total string quantity ； 06 Tighten all the main bolts evenly, making sure to do so diagonally ； 07 Attach a dial indicator to the shaft and rotate the shaft while using the indicator to check the balance disk; the tolerance should meet the requirements specified in the drawings, and generally should not exceed 0.06 ； 08 When installing the thrust bearing, attention should be paid to adjusting the clearance of the balance disk; the adjustment ring located in front of the bearing should be used to set this clearance to the value specified in the drawings. There are corresponding standards for the maintenance of each component of a centrifugal pump, and these standards must be strictly followed during maintenance. 6) Pump shaft 01: Clean and inspect the pump shaft; it should be free from cracks, severe wear, or other defects. If there is wear, cracks, erosion, etc., it should be recorded in detail and the causes analyzed. 02 Check the straightness of the pump shaft of the centrifugal oil pump; this value should not exceed 0.05 mm over its entire length. The journal surface must be free of defects such as pitting and grooves; the maximum allowable value for surface roughness is 0.8μm, and the errors in roundness and cylindricity of the journal should be less than 0.02mm. 03 The parallelism error between the center line of the keyway in the centrifugal pump and the axis center line should be less than 0.03 mm/100. 7) Impeller 01: Clean and inspect the surfaces of each stage of the impeller. The impeller surfaces should be free from defects such as cracks or wear; the flow channels on the impeller surface should be smooth, without any scaling or burrs. The blades should also be free from cracks or thinning due to erosion. 02 Check the sealing rings at the inlet and outlet of the impellers at all levels; they should not be loose, and their surfaces must be smooth without any burrs. The maximum allowable value for surface roughness Ra is 0.8μm, while the assembly clearance between the impeller and these sealing rings should be between 0.05 and 0.10 mm. Taking the inner hole of the impeller as a reference, the radial runout of the impeller should not exceed 0.05 mm. The end face runout shall not exceed 0.04 mm. 03 The impeller and shaft are fitted with an interference fit, typically H7/h6. The interference fit between the key and the keyway is 0.09–0.12 mm, resulting in a clearance at the top of the centrifugal pump key after assembly of 0.04–0.07 mm. 04 The rotor must be in static balance. 8) Pump head, pump casing, and impeller: 01 Clean and inspect each stage of the impellers; there should be no defects such as wear, cracks, or erosion. 02 The anti-rotation pin of the impeller in the centrifugal pump should be free of bending, breaking, and loosening. The surfaces of the pump head and the seal ring of the pump casing should be free of pitting, scratches, or grooves. The maximum allowable value for surface roughness Ra is 0.8μm. The fitting clearance between the seal ring, the pump head, and the pump casing of the centrifugal pump should be between 0.05 and 0.10 mm, and the seal ring must not be loose. 03 Using the impeller of the centrifugal pump and the flange of the pump casing as references, measure the radial runout of the inner diameter of the sealing ring; this value should not exceed 0.50 mm, while the end face runout should not be more than 0.04 mm. 04 Measure the gap between the seal ring of the centrifugal pump’s impeller and casing and its assembly seal ring; this value should be between 0.50 and 0.60 mm. 9) Bearing 01: Sliding bearing. (1) The interference fit between the bearing and the bearing cover should be 0.02–0.04 mm; the lower bearing liner should make even contact with the bearing housing, with the contact area being at least 60% larger. (2) When replacing the bearing, the contact angle between the shaft journal and the lower bearing should be 60–90°; the contact area must be even, with no fewer than 2–3 contact points per square centimeter. (3) The bearing alloy layer must be firmly bonded to the bearing lining; the surface of the alloy layer shall be free from defects such as pores, inclusions, and flaking. (4) The clearance at the top bearing shall comply with the provisions in the table below. (5) The data for the bearing side clearance on the horizontal midplane is half of the top clearance. 02 Rolling bearings (1) The fit between rolling bearings that bear axial and radial loads and the shaft is H7/js6. (2) The fit between a rolling bearing that bears only radial loads and the shaft is H7/k6. (3) The fit between the outer ring of the rolling bearing and the inner wall of the bearing housing is Js7/h6. (4) For pumps that use rolling bearings for axial thrust support, an axial clearance of 0.02–0.06 mm should be provided in the outer ring of the rolling bearings. (5) When assembling or disassembling rolling bearings, the temperature used for hot fitting should not exceed 100°C; direct heating with flames is strictly prohibited. (6) The rolling elements of the rolling bearing, as well as the oil and the surface of the raceways, should be free from corrosion, pits, and spots; the contact should be smooth with no abnormal noises. 10) Coupling 01: The fit between the coupling and the shaft is H7/js6. 02 The axial clearance between the two end surfaces of the coupling is generally 2 to 6 mm. 03 When installing a toothed coupling, it should be ensured that the outer teeth are located in the middle of the width of the inner teeth. 04 When installing an elastic ring pin coupling, the elastic ring and pin should be in an interference fit, with a certain degree of tension. The diameter clearance between the elastic pin and the coupling hole is 0.40～0.60 mm. 11) Rotor 01: Circular runout of the rotor. (1) The tolerance value for the circular runout of the rotor in single-stage centrifugal pumps shall meet the requirements specified in the table. (2) The circular runout of the rotor of multi-stage centrifugal pumps shall meet the requirements specified in the table. 02 For multi-stage pumps, the rotor should be dynamically balanced when necessary, and the requirements for this balancing must comply with the technical specifications. The fit between the shaft sleeve and the shaft is H7/h6, with a surface roughness of ▽1.6. 04 The fit between the balance and the shaft is H7/js6. 05 Impeller (1) The fit between the impeller and the shaft is H7/js6. (2) The impeller must be in static balance; for impellers operating at a speed of 3000 r/min, the allowable residual unbalanced weight on the outer diameter shall not exceed the values specified in the table. (3) The impeller is balanced using the weight-removal method; at appropriate locations, a portion of the material is removed such that the thickness removed does not exceed 1/3 of the wall thickness. (4) For hot oil pumps, when assembling the impeller and shaft, a clearance of 0.10–0.40 is left at the key top, and the axial clearance between the impeller and the front and rear partition plates should be no less than 1–2 mm. 12) Sealing 01 Mechanical seal: (1) The diameter clearance between the gland and the shaft sleeve is 0.75～1.00 mm, and the thickness of the gasket in the gap between the gland and the seal is 1～2 mm. (2) The roughness of the contact area between the sealing gland and the static ring seal is ▽3.2. (3) The shaft or sleeve at the location where the mechanical seal is installed must be free of defects such as rust spots or cracks, with a surface roughness of ▽1.6. (4) An axial clearance of 1–2 mm should be maintained between the root of the anti-rotation groove at the tail end of the stationary ring and the top of the anti-rotation pin. (5) The performance of the spring after compression shall meet the design requirements, with a deviation of ±2mm. (6) The rotation direction of the mechanical seal ring spring should be opposite to that of the pump shaft. (7) The gland bolts should be tightened evenly to prevent the gland end face from tilting. 02 Packing Sealing (1) The diameter clearance between the seal oil ring and the shaft sleeve is generally 1.00～1.50 mm. (2) The diameter clearance between the oil seal ring and the packing box is 0.15～0.20 mm. (3) The diameter clearance between the filler gland and the shaft sleeve is 0.75～1.00 mm. (4) The clearance between the filler gland and the diameter of the filler box is 0.10～0.30 mm. (5) The diameter clearance between the filler base sleeve and the shaft sleeve is 0.70～1.00 mm. (6) The diameter clearance between the pressure reduction ring and the shaft sleeve is 0.50 to 1.20 mm. (7) The outer diameter of the packing ring should be 0.30–0.50 mm smaller than the bore diameter of the packing box, while its inner diameter should be 0.10–0.20 mm larger than the shaft diameter; the cut angle should be 45° to the axial direction. (8) During installation, the cuts of two adjacent layers of filling material should be offset by at least 90°. 13) The cylindricity of the main shaft 01 neck is 1/4000 of the shaft diameter, with a maximum value not exceeding 0.025; the surface must be free from defects, and the roughness should be ▽1.6. 02 Using the two journal shafts as a reference, the radial runout tolerance for the coupling and the middle section of the shaft is set at 0.04 mm. The key and the keyway must fit tightly together; no shims are allowed. The interference between the key and the keyway should meet the requirements specified in the table. The diameter clearances between the shell mouth ring and the impeller mouth ring, as well as between the intermediate bracket and the intermediate shaft sleeve, shall meet the requirements specified in the table. When performing maintenance on a multi-stage pump, if possible, it is best to first review the manufacturer’s maintenance instructions and general assembly drawings to identify any special considerations. 14) Packing gland 01: The end face of the packing gland must be perpendicular to the axis. 02 The clearance between the packing gland and the shaft sleeve diameter should be 0.75～1.0 mm. 03 The gap between the outer diameter of the packing gland and the packing box is 0.1～0.15 mm. 04 The gasket of the mechanical seal gland should be 1.50～2.50 mm above the contact surface. 15) Sealing ring 01: The clearance between the sealing ring and the shaft sleeve should be 1.00～1.50 mm. 02 The outer diameter of the sealing ring is perpendicular to its end face. 03 The clearance between the filler box and the outer diameter of the oil-sealing ring is 0.15～0.2 mm. 16) Coupling 01: The planar clearance of the coupling is 2.2～4.2 mm for cold oil pumps, and 1.55～2.05 mm greater than the aforementioned value for hot oil pumps. 02 The rubber ring for couplings is 0.15～0.35 mm smaller than the bore diameter. 03 Use special tools when removing the coupling to maintain its smoothness and avoid damage. 17) Shafts and bushings: The allowable bending of shaft diameter 01 is not more than 0.013 mm; for pumps with low rotation speeds, this value is not more than 0.07 mm in the middle section of the shaft, while for pumps with high rotation speeds it is not more than 0.04 mm in the middle section of the shaft. The surface of axis 02 is smooth, without cracks, wear, etc. The surface of the 03 bearing sleeve should maintain a Ra value of 1.6 um. The 04 shaft and sleeve use H7/h6. 2. Analysis of the reasons for motor burnout 1) Motor overheating. The main characteristic of a motor burning out is overheating; therefore, some believe that the cause of motor burnout is overheating of the stator windings, and it is thought that by measuring the stator temperature for protection purposes, the motor can be prevented from burning out. In fact, this is not the case; the heating and cooling of motors is a rather slow process. Therefore, only by installing temperature sensors in large and medium-sized, important motors can effective overheat protection be implemented. It is quite uneconomical for small motors. 2) Motor overload: In some applications, the load on the motor remains almost constant, so it seems unnecessary to install overcurrent protection. But sometimes stall can occur, causing the motor to overload and burn out. Therefore, protection with a reverse-time characteristic is required against motor overload, which is generally provided by an overcurrent relay or a thermal relay. 3) Motor phase loss: Most motor damages are caused by a missing phase. Burnout failures caused by phase loss account for 80% of all motor burnouts. It has long been believed that operation with a missing phase will cause the motor windings to overheat and get damaged, and that using temperature sensors to monitor the temperature rise of the windings is the most direct and effective method for phase loss protection. But in reality, if the motor operates with a missing phase, it will burn out in a very short time. Neither relying on traditional inverse-time characteristic protection nor using temperature monitoring can protect the motor against phase loss. Another view is that operation of the motor with a missing phase will result in an electromotive force several times higher than the rated voltage appearing across the windings at the moment of phase loss, causing the motor windings to break down and get damaged. Practice has shown that motor damage caused by a broken phase is resulting from inter-turn breakdown and short circuit, with no heating occurring in the stator windings at all. Both the actual conditions and test results show that the high-voltage back EMF generated across the open-phase winding at the moment of phase loss causes far greater damage to the motor than the damage caused by overheating. Therefore, motors of any wiring type should be equipped with phase loss protection, and this protection must be able to operate instantaneously.