Maintenance, repair, and servicing of rotating equipment

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Maintenance and repair of moving equipment: Moving equipment is an essential component for the proper operation of factory production; therefore, maintaining and repairing this equipment is necessary to ensure its proper functioning. 1. Types of equipment maintenance 2. Maintenance of centrifugal pumps 3. Maintenance of compressors 4. Maintenance of fans I. Types of equipment maintenance A. Planned maintenance: Maintenance that is carried out according to a plan developed based on the management experience related to production equipment and its current condition. Depending on the content, frequency, and requirements of the maintenance, it can be further classified into minor maintenance, medium maintenance, and major maintenance. Regular maintenance has two shortcomings: 1. When potential safety hazards exist in the equipment, these cannot be eliminated in a timely manner due to the fact that it is not yet time for maintenance. 2. Even if the equipment is in good condition, it still needs to be repaired when the maintenance schedule arrives. This repair process is highly arbitrary, leading to waste of human and material resources, as well as poor repair results. Therefore, the personnel responsible for formulating equipment maintenance plans require a very high level of experience. B. Unplanned maintenance: Unplanned maintenance refers to the need for maintenance to be carried out without shutting down the equipment, or with shutdown, when a fault or accident occurs suddenly during its operation. Characteristics of unplanned maintenance: Maintenance is difficult to predict in advance, making it impossible to establish a maintenance schedule; moreover, it requires short maintenance times, high quality of work, complex maintenance environments and operating conditions, as well as significant challenges in carrying out the maintenance. The maintenance ratio is high. II. Minor maintenance tasks for centrifugal pumps: 1. Replace the packing seal. 2. For double-support pumps, inspect and clean the bearings, bearing housings, oil shields, water shields, oil gauges, etc., and adjust the bearing clearance. 3. Check and repair the alignment of the coupling as well as that of the drive unit and the pump. 4. Handle common defects that occur during operation. 5. Inspect and clean the cooling water, seal oil, and lubrication systems. Major repair projects: 1. Include minor repair projects. 2. Inspect and repair the mechanical seal. 3. Inspect each component for wear, corrosion, and erosion during disassembly. Non-destructive testing is performed on the pump shaft and impeller when necessary. 4. Inspect and clean bearings, oil seals, etc., and measure and adjust the clearance of bearing oil seals. 5. Check the circular runout and clearances of various parts of the rotating shaft, and perform dynamic balancing tests if necessary. 6. Check and correct the straightness of the shaft. 7. Measure and adjust the axial play of the rotor. 8. 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. During disassembly: 1. Before removing the thrust bearing, use a dial indicator to measure the clearance of the balance disk and record it ； 2. 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 ； 3. Small components that are difficult to mark (such as keys) can be placed together with impellers or vanes of the same level (in the middle section), etc ； 4. During disassembly, one can visually check whether there are any abnormal parts, such as loose fits, etc. During maintenance: 1. Visually check whether the surfaces of all components are in good condition; all mating surfaces must be free from dents, scratches, or rust ； 2. Use measuring tools to actually check whether the tolerances of the key fit areas are within acceptable limits ； 3. Check whether the clearances at the impeller seal ring, casing seal ring, guide vane seal ring, inter-stage shaft sleeves, etc., are within the allowable range; those that are excessively worn need to be replaced ； 4. Check whether the bearing is in good condition ； 5. It is best to replace all seals and gaskets with new ones. During reinstallation: 1. First, install the rotor and conduct a dynamic balance test again ； 2. 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 ； 3. The total rotor string length should be measured before installing the balance disc ； 4. After installing the balance disk, measure the rotor’s half-string length ； 5. 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 ； 6. Tighten all the main bolts evenly, being careful to do so diagonally ； 7. Attach a dial indicator to the shaft and rotate the shaft while using the indicator to check the balance disc; the tolerance should meet the requirements specified in the drawings, and generally should not exceed 0.06 ； 8. When installing the thrust bearing, attention should be paid to adjusting the clearance of the balance disk; the adjustment ring in front of the bearing should be used to set the balance disk 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. Pump shaft 1: Clean and inspect the pump shaft; it should be free from cracks, severe wear, or other defects. If there is any wear, cracking, erosion, etc., these should be documented in detail and their causes analyzed. 2. 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 the roundness and cylindricity of the journal should be less than 0.02mm. 3. The parallelism error between the centerline of the keyway and the centerline of the shaft in centrifugal pumps should be less than 0.03 mm/100. Impeller 1: 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. 2. 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 0.8 μm, 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. 3. 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. 4. The impeller must be in static balance. Pump head, pump casing, and impeller: 1. Clean and inspect each stage of the impellers; there should be no defects such as wear, cracks, or erosion. 2. The anti-rotation pin of the impeller in the centrifugal pump should be free from bending, breaking, and loosening. The surfaces of the pump head and the sealing ring of the pump casing shall be free from pitting, scratches, and grooves. The maximum permissible value for surface roughness Ra is 0.8 μm. The assembly clearance between the sealing ring and the pump head as well as the centrifugal pump casing should be 0.05–0.10 mm; the sealing ring must not be loose. 3. 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 exceed 0.04 mm. 4. Measure the gap between the impeller of the centrifugal pump, the seal ring of the pump casing, and the assembly seal ring; this value should be between 0.50 and 0.60 mm. Bearings 1. Sliding bearings (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 seat, with the contact area being at least 60% larger. (2) When replacing the bearings, 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 liner; 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. 2. 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 is subjected only to 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 in which rolling bearings are used for axial thrust support, an axial clearance of 0.02–0.06 mm should be maintained between the outer rings of the rolling bearings. (5) When installing or removing rolling bearings, the temperature used for hot installation shall 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. Coupling 1. The fit between the coupling and the shaft is H7/js6. 2. The axial clearance between the two end faces of the coupling is generally 2 to 6 mm. 3. 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. 4. When installing the 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. Rotor 1. 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 of the table. 2. For multi-stage pumps, the rotor shall be dynamically balanced when necessary; the requirements thereof shall comply with the technical specifications. 3. The fit between the shaft sleeve and the shaft is H7/h6, with a surface roughness of ▽1.6. 4. The fit between the balance and the shaft is H7/js6. 5. 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 partitions should be no less than 1–2 mm. Sealing 1. 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 operation 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 becoming skewed. 2. Packing seal (1) The diameter clearance between the sealing 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 packing gland and the diameter of the packing box is 0.10～0.30 mm. (5) The diameter clearance between the filler bottom sleeve and the shaft sleeve is 0.70～1.00 mm. (6) The diameter clearance between the reduction ring and the 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°. Spindle 1: The cylindricity of the 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. 2. 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. 3. The key and keyway must fit tightly together; no shims are allowed. The interference between the key and keyway shall 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 support ring 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. Gland packing 1. The end face of the gland packing must be perpendicular to the axis. 2. The clearance between the packing gland and the shaft sleeve diameter should be 0.75～1.0 mm. 3. The clearance between the outer diameter of the packing gland and the packing box should be 0.1～0.15 mm. 4. The gasket of the mechanical seal gland should be 1.50–2.50 mm above the contact surface. Sealing ring 1. The clearance between the sealing ring and the shaft sleeve is 1.00～1.50 mm. 2. The outer diameter of the oil seal ring is perpendicular to the end face. 3. The clearance between the filler box and the outer diameter of the oil-sealing ring is 0.15～0.2 mm. Coupling 1. Planar clearance of the coupling: 2.2–4.2 mm for cold oil pumps; for hot oil pumps, it is 1.55–2.05 mm more than the aforementioned value. 2. The rubber ring for the coupling should be 0.15–0.35 mm smaller than the bore diameter. 3. Use special tools to disconnect the coupling, and keep it smooth to avoid damage. Shaft and sleeve: 1. The allowable bending of the shaft diameter 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. 2. The surface of the shaft is smooth, without cracks, wear, etc. 3. The surface of the shaft sleeve shall maintain Ra=1.6um. 4. The shaft and sleeve use H7/h6. III. Compressor maintenance: Since compressors operate at high speeds during system operation and are highly precise mechatronic devices, they often develop faults in practical use. The compressor host is the core component of the compressor, operating at high speeds continuously; it must undergo preventive major repairs after operating for a certain period of time or number of years. If there are problems with the compressor motor, if the suction and exhaust valves of the compressor do not close properly, or if the thermal protector malfunctions, replacement should be carried out. For problems such as the compressor shaft getting stuck or the cylinder being jammed, repair attempts can be made first; the specific methods are as follows: (1) The tapping method: After turning the machine on, use a wooden hammer to tap the lower part of the compressor, so that the stuck components inside the compressor vibrate and start moving. (2) Capacitor start method: A capacitor with a larger capacitance than the original one can be connected to the circuit for starting. (3) High-voltage start method: The power supply voltage can be increased using a voltage regulator before starting. (4) Pressure relief method: Start the system after releasing all the refrigerant from it. If the above methods do not work, the only option is to replace the compressor with a new one. The major overhaul of the compressor includes the following components: A. Overhaul of the main unit and gearbox: Replace the rotating bearings of the main unit rotor; replace the mechanical shaft seals and oil seals of the main unit rotor; replace the adjustment shims of the main unit rotor; replace the sealing gaskets of the main unit rotor; replace the composite gaskets of the main unit rotor; adjust the precise clearance of the main unit rotor; replace the primary/secondary rotating bearings of the gearbox; replace the mechanical shaft seals and oil seals of the gearbox; adjust the precise clearance of the gearbox; adjust the precise clearance of the gearbox gears. B. Lubricate the motor bearings with grease. C. Inspect or replace the coupling. D. Clean and maintain the air cooler. E. Clean and maintain the oil cooler. F. Inspect or replace the oil stop valve. G. Inspect or replace the unloading valve. H. Clean the water-vapor separator. I. Replace the engine oil. J. Clean all the heat dissipation surfaces of the unit. K. Check the operation of all electrical components. L. Check all protection functions and their set values. M. Inspect or replace all pipelines. N. Check the contact conditions of all electrical components. IV. Overhaul of the fan: A. Overhaul of centrifugal fans. Inspection before overhaul: Before carrying out the overhaul, the fan should be inspected while it is in operation, so as to identify any defects present and record relevant data for reference during the overhaul process. The main items of inspection include: 1. Measuring the vibration of the bearings and motor as well as their temperature rise. 2. Check for oil leakage from the bearing seal. If the fan uses sliding bearings, it is necessary to check the operation of the oil system and cooling system as well as the quality of the oil. 3. Check the tightness of the connection between the fan housing and the duct flange. Check whether the external connection of the inlet baffle is proper and whether the switch operates smoothly. 4. Understand the relevant data during the operation of the fan, and conduct efficiency tests on the fan if necessary. Maintenance of fans 1. Maintenance of the impeller (1) Welding and repairing blades. (2) Replace the blade. 2. Replace the impeller. 3. Replace the anti-wear plate. 4. Inspect the shaft. 5. Replace the hub. 6. Inspect and replace the bearings. 7. Inspect the casing and guiding devices. Fan trial operation: 1. The fan should be tested after maintenance, with a trial operation time of 4–8 hours. 2. In the event of any abnormalities during trial operation, the fan should be stopped immediately to determine the cause. 3. During the trial run, the vibration of the bearings (vertical vibration) should generally be 0.03 mm, with a maximum of 0.09 mm; the shaking of the bearings (horizontal vibration) should generally be 0.05 mm, with a maximum of 0.12 mm. 4. The bearing temperature during trial operation should not exceed 70°C. 5. The fan is operating normally with no abnormal noises. 6. The baffle switch is flexible and provides correct indication. 7. All seals are intact, with no oil leakage, air leakage, or water leakage. B. Inspection of axial flow fans – Inspection of the fan 1. Inspection of the impeller (1) Inspection of the blades (2) Inspection of the blade shafts (3) Inspection of the hub 2. Inspection of the control mechanism The inspection items include: ① Whether there is severe wear at the connection between the electric actuator (or hydraulic actuator) and the lever, and whether it rotates smoothly. ② Check whether the lever has any cracks or bending deformations; if there are cracks or bending deformations, it must be replaced. ③ There should be no severe wear at the connection between the lever and the drive shaft, and the drive shaft should move smoothly. ④ The connecting rod should be free of cracks and bending deformations; any cracks or bending deformations in the connecting rod require replacement. ⑤ The connection screws between the linkage and the converter should be in good condition; if they are found to be loose, they should be tightened again. ⑥ The guide post should be free of cracks and bending deformation, and should rotate smoothly. ⑦ The bearings at the petiole, converter, support rod, guide post, sealing cover, etc., should be in good condition, the clearances should meet the standards, and they should be properly lubricated. ⑧ Check the converter sleeve for cracks, stains, and corrosion. ⑨ Check whether the entire adjustment mechanism operates smoothly. If there is any sticking or difficulty in movement, the thickness of shims or the length of levers at locations such as connecting rods, levers, and drive shafts can be adjusted as needed until proper operation is achieved. 3. Inspection of guide vanes: The inspection items include: ① The wear condition of the guide vanes as well as their inner and outer rings; when the guide vanes are severely worn, welding or replacement is required ； The inner and outer rings should be intact, without severe deformation. ② The guide vanes should be secure without any looseness, and the fasteners must be intact. ③ The inlet and outlet angles of the outlet guide vanes should meet the design requirements: the inlet should face directly the airflow coming from the impeller, while the outlet should be aligned with the axis.