Screw Compressor Maintenance Procedures

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Screw compressors belong to the category of positive-displacement compressors; the pressure of the gas inside the compressor is increased by reducing its volume. It is a fixed-speed screw air compressor unit driven by a Y-type explosion-proof motor. 1. General Provisions 1.1 Scope of Application These procedures apply to the maintenance and repair of the screw compressors B4001-1/2/3 used in the gas generation process (model: LG66/0.7, manufacturer: The 711th Research Institute of China State Shipbuilding Corporation). 1.2 Structure and Technical Performance
1.2.1 Overview
Screw compressors are positive displacement compressors; in these machines, the pressure of the gas is increased by reducing its volume. It is a fixed-speed screw air compressor unit driven by a Y-type explosion-proof motor. The screw compressor is driven by a motor, and its rotation speed is increased to the rated value through speed-increasing gears; these gears are installed in front of the compressor’s suction side and belong to an internal-mounted design. The motor and compressor are mounted on the same fixed base frame. The compressor is also equipped with necessary auxiliary equipment such as an oil system, water system, gas system, instruments, and an electrical control system. The compressor delivers 66 m3/min of CO gas at the inlet condition, with an exhaust pressure of 0.7 MPa (gauge pressure). The compressor rotor has a diameter of 255 mm, with an SRM asymmetric tooth profile. 1.2.2 Host structure 1.2.2.1 Housing: The housing assembly divides the cylinder block into five major components using several vertical partitions – the front face, intake seat, cylinder block, exhaust seat, and rear cover – all of which are made of cast iron. 1.2.2.2 Rotor: The material used is 2Cr18 forged steel, and an SRM asymmetric profile is employed. The male rotor has four teeth while the female rotor has six teeth. The male rotor is connected to the motor through a pair of gears, with a metal flex coupling in between. An oil seal is installed at the shaft extension to prevent oil from leaking from the front cover. One end of the female rotor features a hexagonal head; by removing the small cover on the rear cover, it is possible to rotate the rotor easily. 1.2.2.3 Bearings: This machine is equipped with three types of bearings: cylindrical roller bearings, tapered roller bearings, and angular contact ball bearings. 1.2.2.4 Shaft seal device: To prevent compressed gas from leaking outward along the rotating shaft and to stop lubricating oil from seeping into the cylinder and contaminating the gas, the unit is equipped with double-end mechanical seals. One mechanical seal is installed at each end of the rotor; each set of mechanical seals is filled with water on the side facing the gas and with oil on the side facing the bearings, thereby serving a sealing and cooling purpose. The water and oil that leak onto the friction surfaces enter the intermediate chamber before being discharged outside the machine. During operation, the water pressure is set to 0.1 MPa higher than the gas pressure, while the oil pressure is set at around 0.25 MPa. 1.2.2.5 Synchronous gear: Installed on the screw shaft on the outside of the compressor’s exhaust end, it ensures that the male and female screw rotors rotate without coming into contact. To facilitate adjustment of the screw meshing clearance, the passive synchronous gear on the female rotor consists of a hub along with thick and thin tooth segments; the thick tooth segments transmit torque, while the thin tooth segments adjust the gear clearance (0.02–0.04), thereby preventing accidental contact on the back side of the rotors when the compressor starts or stops. 1.2.2.6 Coupling: The coupling used in this unit is a metal laminated flexible coupling. It enables the transmission of the torque generated by the motor to the compressor, and it can compensate for the axial and radial deviations that occur between the motor and the compressor due to manufacturing errors, installation errors, deformation under load, and temperature changes. The laminated flexible coupling utilizes metal flexible elements to transmit torque, compensate for three-dimensional displacement of the two shafts, reduce shocks, isolate vibrations, and ensure the smooth operation of the unit. 1.2.2.7 Speed increase gear: The speed increase gear is located on the intake side of the compressor; one of the gears is fitted over the shaft end of the male rotor. The drive shaft and the female rotor are on the same axis, but they do not transmit power directly to each other, with a driving gear mounted on the drive shaft. 1.2.3 Main technical specifications: Table 1. Displacement: 66 m3/min; Inlet pressure: 0.098 Mpa (absolute pressure); Exhaust pressure: 0.45 Mpa (absolute pressure); Inlet temperature: ≤40°C; Exhaust temperature: ≤80°C; Compressor speed: 3261 r/min; Shaft power: 180 kw; Motor power: 220 kw; Drive method: Motor-driven with speed control and frequency conversion. 2. Standards for good condition: 2.1 Parts and components: 2.1.1 The parts and components of the main and auxiliary machines are complete and in good condition, with quality meeting the required standards. 2.1.2 Instruments, meters, signals, interlocks, and various safety devices as well as automatic control devices are complete, functional, and accurate; the operation rate of starting switches, signals, and interlock devices is 100%, and the regular inspection rate for meters is 100%. 2.1.3 The foundation and base are stable and reliable, with all anchor bolts properly connected and tightened. The specifications of bolts in each group are uniform, with 1–3 threads exposed. 2.1.4 Safety devices such as pipelines, fittings, valves, and supports are reasonable, firmly installed and intact, clearly marked, and meet the requirements. 2.1.5 The anti-corrosion, insulation, and anti-freezing facilities are complete and effective. 2.2 Operating performance
2.2.1 The equipment is properly lubricated; the lubrication system is unobstructed, and the quality of the oil meets the requirements. The principles of “five fixed points” and “three-stage filtration” are implemented. 2.2.2 There are no abnormal vibrations, looseness, noises, or similar issues. 2.2.3 Operating parameters such as temperature, pressure, flow rate, and current in each section meet the requirements of the regulations. 2.2.4 Production capacity reaches the designed capacity. 2.3 Technical documents 2.3.1 Include product certificates of conformity, quality certificates, user manuals, and general assembly drawings. 2.3.2 There are installation, commissioning, and acceptance documents. 2.3.3 The filling of equipment records, maintenance, and acceptance records is timely, accurate, and complete. 2.3.4 There is statistics on equipment operation time and cumulative running time, with an accuracy of 100%. 2.3.5 The spare parts of the equipment come with drawings. 2.3.6 The equipment operation procedures and maintenance rules are complete. 2.4 Equipment and Environment 2.4.1 The equipment is clean, with no dust or grease on its surfaces. 2.4.2 The foundation and its surrounding area are clean and tidy. 2.4.3 There are no leaks in equipment, pipelines, valves, etc. 3. Equipment Maintenance 3.1 Routine Maintenance 3.1.1 Start, operate, and shut down the equipment in strict accordance with the operating procedures, and keep proper records. 3.1.2 Strictly implement the \"Equipment Lubrication Management System\"; top up lubricating oil as specified, and replace it immediately if its quality does not meet the requirements for use. 3.1.3 Check the operation of the oil circuit system; the lubricating oil pressure should be maintained at 0.4 MPa. If the fuel level in the tank drops, new fuel should be added promptly ； If the oil level in the tank rises, the cause should be identified promptly (it could be a leak in the oil cooler) to prevent abnormal wear and tear on the equipment. 3.1.4 Regularly check the pressure and temperature of each component, and keep records as required. If any abnormalities are detected, promptly identify the cause and take action to address it. 3.1.5 The cooling water pressure is maintained within the required range. 3.1.6 Equipment and the work site must be kept clean, with any leaks or spills promptly addressed. 3.1.7 When the equipment is not in use for an extended period, it should be properly maintained, with a shaft rotation check performed once per week. 3.2 Regular inspections The items, cycles, contents, and standards for regular inspections are shown in Table 2. Table 2: Criteria for determining the inspection cycle of various items, as well as the recommended instruments for use. For lubricant quality analysis every three months, a lubricant quality tester is required in accordance with the technical standards for lubricants. Vibration levels should be checked twice a week; a vibration meter compliant with ISO2372 standards is needed for this purpose. Temperature should be monitored twice a week, with changes in temperature determined using a thermometer as specified in these procedures. Instrument devices must be inspected and calibrated on a regular basis in line with the scheduled maintenance cycles, to ensure that their accuracy and sensitivity meet the specified performance parameters. Safety interlock devices should be checked every 12 months to ensure they function properly and reliably in accordance with the established technical requirements. 3.3 Common fault handling methods: The symptoms, causes, and solutions for common faults are listed in Table 3. Table 3: Methods for Handling Fault Causes
Compressor fails to start:
1. Electrical faults
2. Excessive cooling water inside the compressor
1. Check the electrical system
2. Spin the compressor a few times to force the water out

Insufficient air volume:
1. Unopened valves in the air system pipeline network, or leaks in the pipes
2. The upper limit set on the pressure controller regulating air volume is too low
3. Low inlet air pressure
4. Clogged inlet air filter
5. Inlet air valve not fully open
1. Close the unopened valves to stop leaks
2. Increase the upper limit pressure of the pressure controller
3. Open the circuit bypass valve
4. Replace or clean the filter element
5. Open the inlet air valve and check the operation of the disc valve and solenoid valve

Decreasing oil pressure:
1. Failure of the oil pump control valve
2. Clogged or leaking suction oil pipe or filter
3. Excessive gear clearance in the oil pump
1. Recalibrate the control valve
2. Clean the filter and oil pipe to eliminate leaks
3. Readjust or replace the component

Rising oil temperature:
1. Insufficient supply of lubricating oil
2. Poor quality or degraded lubricating oil
3. Abnormal wear on bearings or gears
1. Inspect and clean the oil circuit
2. Replace the lubricating oil
3. Check and adjust, replacing it if necessary

Excessively high exhaust temperature:
1. Insufficient water spray volume
2. Exhaust pressure exceeding the rated value
1. Increase the water spray volume
2. Adjust the exhaust pressure

Overcurrent:
1. Low voltage in the power supply grid
2. Exhaust pressure exceeding the rated value
1. Check the power supply lines and resolve any abnormalities
2. Adjust the exhaust pressure

Compressor fails to reach the rated pressure:
1. Unopened valves in the air system pipeline network, or leaks in the pipes
2. The upper limit set on the pressure controller regulating air volume is too low
3. Low inlet air pressure
1. Close the unopened valves to stop leaks
2. Increase the upper limit pressure of the pressure controller
3. Open the circuit bypass valve

3.4 Emergency shutdown: An emergency shutdown should be carried out in any of the following situations. a. Lubricant supply interruption ； b. Cooling water interruption ； c. Bearing temperature exceeds the limit ； d. Sudden over-temperature and over-pressure of compressed gas ； e. The sound becomes abnormally sudden, with no identifiable cause ； f. Sudden severe vibrations; no cause can be found ； g. Breakage of main components, parts, or pipelines ； 4. Maintenance Cycle and Contents 4.1 Maintenance Cycle The maintenance cycle is shown in Table 4. Table 4 Maintenance categories: Minor repair, Medium repair, Major repair; Maintenance cycle: 3–6 months, 6–12 months, 12–36 months. 4.2 Maintenance contents: 4.2.1 Minor repair: 4.2.1.1 Inspect and tighten bolts in various parts. 4.2.1.2 Check the oil level, oil quality, filter, oil cooler, and oil pump in the tank. 4.2.1.3 Eliminate other defects. 4.2.2 Medium repairs 4.2.2.1 includes minor repair items. 4.2.2.2 Check the wear condition of the tooth surfaces of the synchronous gears and speed-increasing gears. 4.2.2.3 Check whether each joint is loose or leaking. 4.2.2.4 Check whether the safety valve is leaking. 4.2.2.5 Check whether the instruments and interlock devices are sensitive and reliable. 4.2.3 Major Overhaul 4.2.3.1 includes medium-overhaul items. 4.2.3.2 Disassemble and clean each component; the removed parts should be arranged neatly. Make proper markings to avoid incorrect installation. 4.2.3.3 Check the wear condition of each component and replace it as necessary. 4.2.3.4 Inspect and clean the oil tank, filter, and cooler. 4.2.3.5 Inspection, cleaning, and commissioning of all valves in the system (including safety valves). 4.2.3.6 Calibration and setting of various measuring and control instruments. 4.2.3.7. Check the condition of the fuselage and foundation, and tighten all foot bolts. 4.2.3.12 Anti-corrosion and insulation of main and auxiliary equipment. 5. Maintenance methods, clearance adjustment, quality standards 5.1 Brief description of maintenance methods Screw compressors are relatively precise machines; care must be taken during disassembly and assembly, with attention paid to maintaining cleanliness and preventing damage ； Special tools must be used when available, in order to protect components such as bearings and gears. 5.1.1 Disassembly of the compressor housing 5.1.1.1 Remove the pressure tapping points and instrument wiring from the compressor. 5.1.1.2 Remove the front cover, then remove the driving gear shaft and pull out the speed-increasing gear. 5.1.1.3 Remove the rear cover, pull out a pair of synchronous gears, then remove the radial thrust bearing and pull out the mechanical seal. 5.1.1.4 Remove the connection bolts between the intake and exhaust bearing housings and the cylinder block, and lift out the intake and exhaust housings by using the lifting bolts. 5.1.1.5 Pull out the rotor. 5.2 Clearance Adjustment and Quality Standards 5.2.1 Adjustment of bearing clearance: Inside the bearing housing, a special tool (mandrel) and a dial indicator are used to adjust the bearing clearance by means of shims, so as to keep it within the range of 0.02–0.04 mm. 5.2.2 Adjustment of the exhaust end face clearance: First, push the rotor to the exhaust side so that the clearance at the exhaust end face is zero. Then, measure the clearance required for the adjustment shims to be installed (denoted as Y). The required clearance at the exhaust end face for this machine is 0.10–0.12; therefore, the thickness of the adjustment shims should be equal to Y – (0.10–0.12). After the bearing housing and cover are in place, the end face clearance must be measured again, and shims should be added (or removed) depending on the resulting clearance value. An excessive end face clearance at the exhaust side can affect the compressor’s exhaust capacity, while too small a clearance can cause friction between the rotor’s end face and the exhaust bearing seat; therefore, it is necessary to keep it within the specified range. 5.2.3 Adjustment of the rotor meshing clearance The meshing clearance between the male and female rotor profiles should be 0.10–0.15. This adjustment must be carried out prior to adjusting the backlash of the synchronizing gears. After adjusting the synchronizing gear backlash, a recheck is necessary; if the value exceeds the specified range, readjustment is required. 5.2.4 Adjustment of the synchronizing gear clearance: Install the thick and thin tooth plates as well as the gear hub at the end of the rotor. First, fix the thick and thin tooth plates to the hub using bolts, and measure the clearance at 4 points. If the measured value is less than the required clearance, slide the thin tooth plate in the opposite direction of rotation; if the measured value is greater than the required clearance, slide the thin tooth plate in the direction of normal rotation. The synchronizing gear clearance must be adjusted to within the range of 0.02–0.04. After adjustment, tighten the fastening bolts between the thick and thin tooth plates and verify the clearance again. Additionally, insert a set screw at the locking hole. 5.2.5 For the installation and alignment of the motor and compressor, flexible couplings are used. To ensure reliability in long-term operation and to avoid excessive vibration, it is required that the end-face runout and outer-circle runout between the compressor and the motor be kept within 0.08 mm. During alignment, two semi-couplings can be used for comparison. 5.2.6 Installation of mechanical seals: Careful attention must be paid when installing mechanical seals. The seal assembly should be wiped clean to remove any impurities or dust, and it must be handled gently without any impact, to prevent damage to the sealing surfaces. 5.2.6 The inspection and maintenance methods as well as quality standards for oil pumps shall be in accordance with the \"Gear Pump Maintenance and Inspection Procedures\". 6. Commissioning and Acceptance 6.1 Preparations before Commissioning 6.1.1 After all maintenance work is completed, the maintenance site must be left clean with no leftover materials or debris. 6.1.2 Fill the fuel tank to the level required by the process. 6.1.3 Preheat the lubricating oil and start the gear oil pump. 6.1.4 The grounding wires of the electrical section are in good condition. 6.1.5 No abnormal phenomena during shaft turning. 6.2 Test run
6.2.1 Air test run
6.2.1.1 Instant start-up; no abnormal phenomena. 6.2.1.2 After startup, run for 5 minutes and inspect all parts. There should be no abnormal noises, unusual vibrations, or overheating; process parameters must remain within the specified range. 6.2.1.3 After running for 2–4 hours, the temperature of each bearing should not exceed 60°C, with no abnormal phenomena observed. 6.2.2 Process gas commissioning The process gas commissioning shall be carried out for 24 hours, meeting the following requirements: a. No overpressure, and the flow rate shall be no less than the original flow rate or the designed capacity ； b. There are no extraneous noises or abnormal vibrations in all parts ； c. Bearing temperature shall not exceed 60℃ ； d. The lubrication system and cooling water system show no leaks, and the oil pressure and water pressure are normal ； e. Well-sealed. 6.3 Acceptance 6.3.1 Acceptance is possible only if the trial run is successful and all maintenance documents are complete. 6.3.2 Led by the Production Equipment Department, with the participation of relevant maintenance units and production units. 6.3.3 Upon successful acceptance, the maintenance personnel fill out the \"Equipment Maintenance and Acceptance Form\" and file it, after which the equipment is officially handed over for production use. 7. Safety precautions for maintenance and repair 7.1 Precautions for maintenance safety 7.1.1 Illegal starting, stopping of equipment, and improper operations are strictly prohibited. 7.1.2 The use of substandard or deteriorated lubricants is strictly prohibited. 7.1.3 It is strictly prohibited to loosen or tighten bolts under pressure. 7.1.4 The rotating exposed parts (couplings) must be equipped with safety protection devices. 7.1.5 During equipment operation, it is prohibited to wipe or inspect the equipment at the rotating parts. 7.1.6 The lifted load must not remain above the operating equipment. 7.1.7 No items unrelated to the operation of the equipment shall be stored on site, and the area must be kept clear. 7.2 Safety Precautions for Maintenance 7.2.1 When maintaining equipment, it is necessary to obtain a maintenance task order, implement reliable safety measures, and obtain approval at various levels in accordance with the regulations for major, medium, and minor repairs. 7.2.2 Park the equipment as specified, relieve pressure, ensure the medium is properly treated, and obtain confirmation from safety management personnel. 7.2.3 Cut off the power supply and hang a sign reading “Under maintenance; do not close the switch.” 7.2.4 Go through the procedures for handing over the equipment for maintenance as required. 7.2.5 Strictly inspect the lifting equipment and tools used for maintenance to ensure they are safe and reliable. 7.2.6 Install blind plates at the locations where they are required to prevent the leakage of media. 7.2.7 Components must be removed in sequence and placed neatly, avoiding any collisions. 7.2.8 Holes and pipe openings in the disassembled equipment should be sealed promptly to prevent debris from falling in. 7.2.9 When using cranes and other lifting equipment, there must be a dedicated person to give instructions, and the ropes must be secured firmly. 7.2.10 When working in cross operations, workers below must wear safety helmets. 7.2.11 When hot work is required, a hot work permit must be obtained and approved in accordance with regulations. 7.2.12 The voltage of temporary lights for maintenance shall not exceed 36 volts. 7.2.13 After the maintenance is completed, the areas that need to be sealed should be carefully inspected to prevent tools, debris, and other items from remaining inside the equipment. 7.2.14 After the maintenance is completed, the blind flanges installed prior to the maintenance should be removed in accordance with the blind flange layout diagram. 7.3 Safety precautions for commissioning 7.3.1 When commissioning equipment after maintenance, a commissioning plan is required (except for minor repairs); the commissioning must be carried out in accordance with this plan after it has been approved. 7.3.2 The testing must be supervised by a dedicated person, with another person responsible for safety and yet another person in charge of the operations. 7.3.3 All preparatory work shall be carried out in accordance with the requirements of Article 6.1 of these regulations prior to trial operation. 7.3.4 During the commissioning process, unauthorized personnel are prohibited from entering the site. 7.3.5 If any abnormality occurs during testing, testing must be stopped immediately; the cause must be identified before resuming testing.