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1 Maintenance and Quality Standards 1.1 Preparations before disassembly 1.1.1 Understand the operating conditions of the fan and have all necessary drawings and documents ready. 1.1.2 Prepare all maintenance tools, measuring instruments, lifting equipment, spare parts, and materials. 1.1.3 The power supply is cut off, and the process conditions meet the requirements for safe maintenance. 1.2 Disassembly and Inspection 1.2.1 Remove all accessories from the fan and check the gaps between the rotors as well as between the rotors and the side walls. 1.2.2 Remove the coupling or pulley, and inspect the elastic ring or V-belt. 1.2.3 Disassemble the gearbox, inspect the tooth surfaces and the bolts that adjust the gears. 1.2.4 Remove the bearings and bearing housings, and inspect the oil seals and bearings. 1.2.5 Remove the sealing components and inspect the labyrinth sleeve, moving ring, stationary ring, O-rings, and other sealing parts. 1.2.6 Remove the wall panels and inspect the wall panels and rotor. 1.3 Quality Standards 1.3.1 Airframe 1.3.1.1 The airframe shall be free from damage and cracks. 1.3.1.2 The levelness of the machine body installation is 0.04 mm/m. 1.3.2 Rotor 1.3.2.1 The rotor surface shall be free from defects such as sand holes, pores, and cracks. 1.3.2.2 The circular runout of the rotor end face shall not exceed 0.05 mm. 1.3.2.3 The rotor is subjected to static balance or balance verification. 1.3.3 The clearances between rotors, as well as the clearances between the rotors and the casing and wall panels, shall comply with the specifications in Tables 2 and 3. Table 2 can be found in SHS 01024—2004 \"Maintenance and Overhaul Procedures for Roots Blowers\". 1.3.4 Shaft 1.3.4.1 The shaft surface shall be smooth, free from scratches, cracks, and similar defects. 1.3.4.2 The cylindricity of the shaft journal shall not be greater than half of the shaft diameter tolerance. 1.3.4.3 The coaxiality of the shaft is 0.03 mm/m. 1.3.5 Couplings or V-belts 1.3.5.1 Couplings a. The alignment of the coupling should have a radial runout error of 0.06 mm, and an end face runout error of 0.05 mm. b. The axial clearance during coupler installation shall comply with Table 4. 1.3.5.2 V-belts a. The belt tension W should be moderate or as specified in Table 5 ； A force W is applied at the center of L in a direction perpendicular to the belt, such that the deflection at this point reaches δ = 0.016L; the value of the force W should then correspond to that in Table 5. Table 4 Axial clearance during coupling installation, in mm. Maximum outer diameter of the coupling: 106–170, 190–260, 290–350. Axial clearance: 2–4, 2–4, 4–6. Table 5 Belt tension, in N. Belt type: 5V, 8V. Minimum value Wmin: 76.2, 121.170. Maximum value Wmax: 101.90, 271.50. b. The deviation at the center of the belt groove shall not exceed 0.05 mm/100 mm. 1.3.6 Bearings 1.3.6.1 Rolling shafts a. The rolling elements and the raceway surfaces should be free of scratches, pitting, or rust; the retainers should be free from deformation or damage. b. The inner ring of the rolling bearing and the shaft are fitted with a H7/k6 fit, while the bearing housing and the outer ring of the bearing are fitted with an H7/h6 fit. c. The rolling bearing must be mounted firmly against the shaft shoulder or a shoulder pad. d. The temperature of the bearings during hot installation shall not exceed 120°C; direct flame heating is strictly prohibited. 1.3.6.2 Sliding bearings: a. After scraping and lapping, the imprint on the bearing surface should be uniform, with generally no less than 2–3 points per cm2; the contact angle is usually between 60–90°. b. The bearing top clearance is shown in Table 6. c. The side clearance is 1/2 of the top clearance. d. The bearing bush and the bearing backing should make good contact, with the contact area generally being over 60%. 1.3.7 Sealing devices 1.3.7.1 The interference fit between the V-ring and the shaft is generally 0.1 mm. 1.3.7.2 The parallelism at both ends of the labyrinth seal sleeve shall not exceed 0.01 mm, and the axial clearance between the seal ring seat and the sleeve is generally 0.2 to 0.5 mm. 1.3.7.3 After the mechanical seal is assembled, the radial runout of the shaft centerline at the moving seal ring shall not exceed 0.06 mm. 1.3.8 Synchronous gears 1.3.8.1 After the gears are fixed with keys, their radial displacement shall not exceed 0.02 mm. 1.3.8.2 The tooth surface contact shall be not less than 50% along the tooth height and not less than 70% along the tooth width. 1.3.8.3 The tip clearance shall be 0.2–0.3m (where m is the module), and the side clearance shall comply with the provisions in Table 7. 2 Maintenance and Troubleshooting 1.1 Routine Maintenance 2.1.1 Check the casing temperature and keep records. 2.1.2 Regularly check the bearing temperature and keep records. 2.1.3 Periodically check for friction or vibration. 2.1.4 Regularly check the lubricant level and whether the oil has emulsified, etc. 2.1.5 Regularly check the pressure difference of the inlet filter. 2.1.6 Regularly check the self-starting function of the standby oil pump motor for high-power fans, as well as the pressure difference across the oil filter. 2.1.7 Use mechanical seals and pressure lubrication, and regularly check the oil pressure and oil temperature. 2.1.8 Regularly check the suction and exhaust pressures. 2.1.9 Periodically check the motor load. 2.1.10 Regularly check whether the cooling water is unobstructed. 2.1.11 Conduct regular inspections and keep records. 2.2 Common Faults and Solutions (see Table 8) Table 8: Common Faults and Solutions Sequence Number Fault Symptoms Cause Solution 1 Fluctuating or insufficient air flow Clogged filter mesh Increased gaps Slipping belt, insufficient rotation Air leakage from pipe flanges Air leakage from shaft seal device Air leakage from safety valve Replace or clean the filter Adjust the gaps or replace the belt Replace the gasket Repair or replace it Grind or replace it 2 Motor overload Clogged filter mesh Increased pressure loss in the pipeline Contact between the impeller and the wall panels Replace or clean the filter Adjust the inlet and outlet pressures Increase the side gaps 3 Overheating Excessive or insufficient oil level, dirty oil, too high or too low oil viscosity Misalignment of the shaft and bearings ； The fan shaft and motor shaft are not aligned; the quality of shaft bearing surface preparation is poor, the contact arc is too small or the contact is inadequate; the gap between the shaft bearing end and the thrust washer is too small; the bearing cover is too tight, with no clearance inside the bearings; the rolling bearings are damaged; the pipe supports are broken, resulting in an increased pressure ratio; the impeller comes into contact with the wall panels – lubricant needs to be added or replaced; align the two shafts to ensure they are concentric, adjust the gaps in the shaft bearings, adjust the bearing covers and gaskets, replace the bearings, and check the inlet and outlet pressures. If there is a gap, tap on the synchronous gears; misalignment of the impeller and gears, poor assembly, abnormal pressure increase due to overload or poor lubrication causing gear damage – correct the alignment according to specifications, reassemble, and investigate the cause of the pressure increase; replace the gears. If the shaft is damaged, change the oil. If the bearing gears are severely damaged or the lubrication is poor or insufficient, replace the lubricant and the bearing gears. Sealing leaks may occur due to the sealing ring not being aligned with the shaft sleeve, shaft bending, or casing deformation, which causes wear on the side of the sealing ring; hard debris may get inside the sealing ring, or the rotor may vibrate excessively, with its radial amplitude being more than half of the radial clearance of the seal; the bearing clearance may be out of spec. The shaft bearing surfaces may not have been prepared properly or may not conform to the design specifications – adjust or replace the belts and couplings, align the shafts, repair or replace them, clean them, check the pressure control valve, repair the relay, adjust the gaps, replace the bearings, and adjust the gaps in all relevant areas or replace the bearings again