Maintenance of centrifugal pumps

Thread Content

Maintenance of centrifugal pumps 1. Preparations before disassembling a centrifugal pump: (1) Obtain the necessary work permits and implement safety measures； (2) Prepare forms for maintenance and understand the assembly standards for each component ； (3) Prepare the tools and measuring instruments required for maintenance ； 2. Disassembly method and sequence for single-stage cantilever centrifugal pumps: (1) The disassembly sequence for single-stage cantilever centrifugal pumps (Y/AY/ZA types) is as follows: ① Remove the coupling guard, and retighten the fixing bolts in the pump base ； ②Remove the intermediate section of the coupling, mark the positioning points of the coupling, measure the distances and record them ； ③Remove the attached pipelines, make proper markings, and drain the lubricating oil from the oil tank ； ④Loosen the gland bolts of the seal to further relieve pressure in the pump. Remove the bolts holding the pump cover in place; note: leave two bolts in place symmetrically before lifting the pump cover ； ⑤Use set screws to evenly push out the pump cover and remove the pump body; those lifting the pump should hold tightly to the inside of the pump-coupling with both hands to avoid hand injuries ； ⑥Transport the pump to the maintenance area and rinse it thoroughly (especially the crude oil and heavy oil pumps). Clean the impeller in the direction of the flow, then remove the impeller backing, the impeller itself, and the key (placing them neatly aside) ； Check the erosion condition of the volute and impeller, as well as the clearance of the mouth ring; if they do not meet the requirements, carry out repairs or replacements. ⑦ Remove the bolts securing the seal gland and those connecting the pump cover, then gently strike the pump cover symmetrically to separate it from the bracket, and pull it out horizontally, applying even force during the process ； ⑧Use a crowbar to pry out the pump shaft sleeve symmetrically. If the sleeve is too tight, use a hammer to strike evenly on the areas where the sleeve meets the shaft at both ends; if necessary, apply heat treatment. Clean the mechanical seal as well and set it aside for future use. Replace it if it is severely worn ； ⑨Fix the dial indicator holder on the bracket securely; measure the shaft’s bending degree and the radial clearance of the bearings, and make corrections or replacements if the values do not meet the requirements. Pull out the rear wheel at Ramallah, then remove the bearing caps at both ends (tap the caps gently with a copper rod to loosen them); check whether the oil seals are aged or worn beyond acceptable limits, and replace them if necessary ； ⑩Remove the bearing lock nut, and use a bearing puller to remove the front and rear bearings (clean them and place them in their proper positions) ； (2) Inspection and testing of various components: 1) Inspection of the pump shaft: ① Its surface should be free of cracks or scratches; there should be no high spots on the mating surfaces. The maximum bending degree should not exceed 0.05 mm, and the ellipticity of the shaft journal should not exceed 1/2000 of its diameter. The key and keyway must fit tightly together – the use of shims is prohibited. The required tightening force is specified in the following table: Shaft journal diameter: 40–70 → Tightening force: 0.009–0.012; 70–110 → Tightening force: 0.012–0.015; 110–230 → Tightening force: 0.012–0.017. When the surface wear on the shaft is less than 0.5 mm, it can be repaired by chromium plating. The chromium coating should not be too thick, as this may lead to its peeling off. The advantage of chromium plating is that it prevents the parts from deforming and eliminates residual stresses ； When there is significant wear or dents, vibration surfacing can be used; prior to welding, the shaft should be rounded and annealed to relieve stress, and after welding, it should be rounded again to meet the technical requirements. ②Inspection of the bearing: The rolling elements and raceways show no pitting or significant wear ； ③Inspection of the coupling: The fit between the rear pulley and the shaft is H7/js6; there are no damages on the surface, and the end face runout is less than 0.05 mm ； 2) Inspection of the impeller and various sealing rings: ① The runout of the rotor shall not exceed the values specified in the table below: Location – Radial runout; Shaft neck, shaft sleeve, ring – Runout value ≤ 0.02, ≤ 0.05, 0.08–0.12. ② The shaft sleeve and the shaft should not be made of the same material; in particular, the same type of stainless steel should not be used to avoid sticking. Before installation, it is necessary to clean them thoroughly and remove any burrs or protrusions ； ③The impeller should be free of sand holes, perforations, cracks, or significant thinning due to erosion. The fit between the impeller and the shaft should be of type H7/j6; a gap of 0.1–0.4 mm should remain at the top of the key. The clearance of the impeller’s ring should comply with the values specified in the table below: For pumps operating at normal temperatures, if the diameter of the ring is less than 100 mm, the clearance should be 0.40–0.60 mm, while the replacement clearance should be 1.20 mm. If the ring diameter is 100 mm or more, the clearance should be 0.60–0.80 mm, with a replacement clearance of 1.50 mm. For hot oil pumps, if the ring diameter is less than 100 mm, the clearance should be 0.60–0.80 mm, and the replacement clearance should be 1.30 mm. If the ring diameter is 100 mm or more, the clearance should be 0.80–1.20 mm, with a replacement clearance of 1.60 mm. 3) Inspection of the volute: ① The sealing surfaces should be free of cracks or high spots; the ring should not be loose, and its clearance should meet the standard requirements. There should be no severe corrosion in the flow channels ； ②Check whether the pump cover gasket can be compressed, and measure the height difference between the pump cover and the volute shoulder. After the pump cover bolts are tightened, a gap of 0.5–3 mm should remain, which can be adjusted by changing the thickness of the pump cover gasket. 4) Inspection of sealing ① The runout of the moving ring shall not exceed 0.03 mm ； ②The radial clearance between the gland and the shaft is 0.75–1.00 mm, and the thickness of the gasket between the gland and the sealing chamber is 1–2 mm ； ③The roughness of the contact surface between the sealing gland and the static ring seal is Ra3.2 ； ④The shaft or sleeve at the location where the mechanical seal is installed must not have any rust spots, cracks, or defects on its surface, with a roughness of Ra1.6 ； ⑤An axial gap 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 ； ⑥The sealing compression amount is 3 mm greater than the shaft play ； ⑦The gap between the bottom sleeve and the shaft sleeve should be 0.4–1 mm. ⑧ The rotation direction of the spring in the mechanical seal for large springs should be opposite to that of the pump shaft ； ⑨The gland bolts should be tightened evenly to prevent the gland end face from becoming skewed ； ⑩After the static ring is installed in the gland, it should be checked to ensure that the ring is not skewed ； (3) Assembly of single-stage centrifugal pumps: ① Heat the front and rear bearings to 100°C using bearing heaters, then install them on the shaft; attach lock washers and locking nuts, tighten them, and secure the washers in place ； ②Insert the shaft into the bearing housing; once it is in place, use a depth gauge to measure the distance from the outer ring of the rear bearing to the edge of the bearing housing, denoting this value as A. Then measure the distance from the protrusion on the bearing cover to the gasket, denoting this value as B. The axial clearance is equal to A-B, and the required range for this value is 0.08–0.12 mm ； ③Adjust the clearance by modifying the thickness of the gland gasket or by adding shims to the outer ring of the bearing. Once the adjustment is proper, apply a small amount of sealant to the gland gasket before installing it; be sure to tighten the bolts evenly and symmetrically ； Heat the mounting rear wheel simultaneously ； ⑤Fasten the stationary and rotating rings properly, ensuring even and symmetrical tightening; install the shaft sleeve gaskets, then insert the shaft sleeve to measure the compression amount ； After adjusting the compression amount, install the impeller and tighten the keys; use a dial indicator to ensure that the runout of the rotating ring is no more than 0.03 – this can be adjusted by varying the tightening force on the rotating ring ； ⑥After making the adjustments, proceed with installation. Once it is confirmed that the mechanical seal moves freely, clean the friction surfaces, apply lubricant to them, and then place them in the sealing chamber. Install the mechanical seal gland; if there is a water jacket, do not tighten it yet. Wait until the pump cover is installed on the bracket and secured before tightening the mechanical seal gland ； ⑦After tightening the pump cover and the mechanical seal gland, press on the shaft sleeve to check whether the compression amount is correct; the positioning screws of the 921 double-faced mechanical seal housing should slide smoothly within the keyway ； ⑧Install the impeller and secure it with the back nut; simultaneously, measure the distance from the mouth ring to the pump cover’s shoulder, as well as the distance from the volute’s shoulder to the housing’s mouth ring – the former value should be less than the latter ； ⑨Install the pump by lifting it; check the sealing gaskets on the pump cover. For high-temperature pumps, it is necessary to prevent insulation materials from reaching the sealing surfaces. When tightening the pump cover, apply even force in a diagonal manner, and ensure even symmetry when doing so ； ⑩Fill with lubricating oil (1/2–2/3 of the oil window), connect auxiliary pipelines and couplings ； ⑪Perform alignment; for detailed methods, see Coupling Alignment. 3. Maintenance of two-stage cantilever centrifugal pumps: The maintenance of two-stage cantilever centrifugal pumps is similar to that of single-stage cantilever centrifugal pumps. It is important to pay attention to the gap between the impeller and the partition (1–4 mm) as well as the gap in the shaft sleeves between stages. The required gaps are as shown in the figure below: For oil coolers, the standard gap is 0.4–0.6 mm; when the capacity exceeds 1000, the gap should be 1.2 mm. For oil heaters, the standard gap is 0.6–0.8 mm; for capacities over 1000, the gap should be 1.5 mm. During installation, the positioning pins of the partition must be installed correctly, with a gap of 2 mm between the top of the pin and the bottom of the slot. The distance from the seal surface of the partition to the seal step on the pump cover is denoted as a, while the distance from the seal surface of the volute to the seal step at the flow channel of the secondary impeller inside the volute is denoted as b. It holds that a < b, and b – a > 0.2 mm. 4. Two-end-supported two-stage single-suction centrifugal pump (150AY150*2): This is a centrifugal pump with a single-suction impeller arranged symmetrically, supported at both ends; it is mainly used as bottom pump in atmospheric-pressure systems as well as high-temperature pumps such as wax oil pumps in coking units. (1) Disassembly: ① Remove the coupling guard; after taking it off, put the fixing bolts back into their holes to prevent them from getting lost. Then disassemble the coupling. Once the bolts are removed, turn the nuts back onto the bolts. Measure the distance between the coupling halves and make a note of it. The backrest wheel should be removed using a specialized puller; hitting it is strictly prohibited ； ②Loosen the machine seal cover, remove the attached pipelines, make markings, and arrange them in their proper places ； ③Drain the lubricating oil, and remove the bearing caps at the rear and front ends ； ④Loosen the rear bearing lock nut and the front bearing sleeve fixing bolts ； ⑤Loosen the bolts holding the front and rear bearing housings, and use jacks to evenly lift the bearing housings out and place them in position ； ⑥Remove the front and rear seals: First, loosen the bolts that secure the shaft sleeve lock nut, then remove the lock nut in the direction of rotation of the impeller. Next, loosen the bolts holding the mechanical seal gland, and take out both the gland and the shaft sleeve ； ⑤Measure the total stroke and record it for reference ； ⑥Remove the bolts securing the pump cover, use a jacking rod to lift the cover; if it is tight, employ a hydraulic separator. Apply even force when lifting the cover, and after removal, clean it and store it properly ； ⑦Loosen the anti-rotation bolt on the partition (be careful not to let it fall into the flow channel). If it is tight, steam heating can be used to loosen it; after that, pull out the rotor and partition together, place them in position, and then clean them ； ⑧Cleaning is complete; now start removing the positioning sleeve, half-circular clasp, impeller, and partition (if the positioning sleeve is tight, use gas welding to heat it) ； (2) Inspection and testing of various components: ① Check the wear condition of the impeller mouth ring; replace it with a new one if the wear is severe ； ②Measure the bending of the shaft; the value at the middle of the shaft should be < 0.05 mm ； ③Measure the clearance of the mouth ring and the inter-stage sleeves; it should fall within the ranges specified in the table below: Unit: mm. Standard clearance: Replacement clearance – First-stage impeller: 0.9–1.5; 2.0. Second-stage impeller: 0.8–1.4; 1.8. Inter-stage shaft sleeves: 0.6–1.2; 1.5. ④ Measure the runout of the rotor: The runout of the mouth ring and inter-stage sleeves should be less than 0.15 mm, while the runout of the sealing surfaces should be less than 0.05 mm. ④ Check whether there are any scratches or deformations on the pump cover gasket and sealing surfaces; if there are high spots, use a flat file to level them out ； ⑤Inspection of bearings and oil seals: For bearings, the rolling elements and raceways should be free of pitting and show no significant wear ； The fit between the bearing sleeve and the bearing meets the H7/h6 standard, and the clearance between the bearing sleeve and the shaft is <0.02mm ； The oil seal shows no signs of aging or cracks ； ⑥Mechanical seal: The rotating and stationary rings have been tested through lapping; the shaft sleeve shows no deformation or cracks. There are no high spots on the contact surface between the stationary ring and the gland, and the inlet and outlet holes are unobstructed. When tightening the rotating and stationary rings, the force applied should be even and symmetrical ； ⑦The semi-circular clip fits tightly with the positioning sleeve ； ⑧Inspection of the coupling: The fit between the rear pulley and the shaft is H7/js6; there are no defects on the surface, and the end face runout is less than 0.05 mm. (3) Assembly: ① First, install the key and the first-stage impeller on the shaft, then place them together inside the pump casing. Next, insert the partition, aligning it with the anti-rotation pin; if it cannot be pushed in by hand, use a copper rod to push it in gently, making sure to do so evenly. Check the clearance of the first-stage impeller within the volute ； ②Insert the secondary impeller and key, tap it into place using a copper rod, install the semi-circular retaining ring and the positioning sleeve, then measure the rotor alignment to determine the distance between the two impellers ； ③Let the height gauge for measuring the seal step of the pump cover be denoted as a, and the depth gauge for the seal surface of the volute be denoted as b; it should be a > b. When installing the pump cover and tightening the bolts, do so symmetrically and evenly ； ④Measure the total play: Push the rotor to the front end and measure a dimension, denoted as A; pull the rotor to the rear end and measure another dimension, denoted as B. The value of B – A represents the total play, which should be recorded. As shown in the figure: ⑤ Install the front and rear end seals, then measure the compression amount. The measurement method is as follows: Push the rotor to the front end and insert the shaft sleeve in place (the key in the shaft sleeve’s keyway fits into the key, ensuring tight fit with the positioning sleeve). Measure the distance from the moving ring surface to the sealing surface in the sealing chamber, denoted as Y. Then measure the distance from the stationary ring’s sealing surface to the gasket in the gland, denoted as X. Thus, the compression amount at the outlet end is L = (X – Y) + half of the total play, while the compression amount at the inlet end is L = (X – Y) – half of the total play. The compression amount can be adjusted by changing the thickness of the graphite gaskets in the seals or the gaskets in the gland. Measure the height of the steps in the sealing chamber and the depth of the sealing grooves in the gland; after making the necessary adjustments, install the water-blocking ring. After installation, do not tighten the bolts yet. Next, install the shaft sleeve gaskets at the front and rear ends along with the locking nuts, and tighten them using a hook wrench. Tighten the set screws symmetrically. ⑥Install the bearing housing at the outlet end, tighten the bolts, and prepare for rotor positioning adjustments. Push the rotor towards the inlet end; measure the distance from the end face of the bearing housing to the inner bearing cover, denoting this value as M. Then measure the distance from the end face of the bearing housing to the shaft shoulder where the bearing is installed, denoting this value as N. If M > N – half the allowable clearance, then shims need to be placed between the outer ring of the bearing and the inner bearing cover, with a thickness of (M – N) + half the allowable clearance ； When M＜N, if N-M equals the half clearance, no shims are needed. If (N-M)＜the half clearance, a shim must be placed between the outer ring of the bearing and the inner retaining ring, with a thickness of: half clearance – (M-N). If (N-M)＞the half clearance, a shim must be placed between the inner ring of the bearing and the shaft shoulder, with a thickness of: (N-M) – half clearance. (Another method is to adjust the rotor to the middle, measure the difference between the shaft step and the inner step of the bearing outer ring, and then level it out.) ⑦After processing the shims, measure again to confirm; once everything is correct, install the bearing (heat it using a bearing heater to <100°C) ； Before installing the bearings, use a dial indicator to verify that the dimensions of the inner and outer shells of the paired bearings are correct. ⑧ Install the oil slinger, octagonal washer, and two locking nuts to secure everything in place ； ⑨Measure the gap between the outer ring of the bearing and the cover; this gap should be in the range of 0.08–0.20 mm. This gap can be adjusted by changing the thickness of the cover shims or by adding shims between the outer ring of the bearing and the step of the cover ； ⑩Install the oil slinger and gland, then install the inlet end bearing housing and bearings ； ⑪Tighten the set screw of the bearing sleeve, and install the oil slinger and gland ； ⑫Lubricant added to the front and rear bearing housings ； ⑬Tighten the machine seal gland, and tighten the set screws of the machine seal shaft sleeve ； ⑭Install the auxiliary pipelines and couplings, and perform alignment; the alignment method is described in Chapter 1. 5. Segmented multi-stage centrifugal pumps (DG type/TDF type) (1) Disassembly of multi-stage centrifugal pumps: ① Remove the coupling guards and associated pipelines, etc., and drain the lubricating oil ； ②Loosen the coupling bolts and remove the intermediate section of the coupling, the diaphragm, and the pump-side coupling wheel (the backup wheel is pulled out using a puller) ； ③Remove the front and rear bearing caps (oil seals), and mark them for proper placement ； ④Remove the front and rear lock nuts, oil slinger rings, and adjustment shims; remove the shaft bearing caps ； ⑤Remove the front and rear bearing housings and bearings (bearing shells), and make proper markings ； ⑥Remove the front and rear end seal covers, (remove the shaft sleeve positioning sleeve and the shaft sleeve seal gasket), pull out the shaft sleeve, and place it in a fixed position ； ⑦Remove the end cover of the pump outlet section, and take off the balance disk, balance plate, or balance drum (pull them out symmetrically using bolts) ； ⑧Remove the pump body tension bolts (mark them at intervals) ； ⑨Remove the outlet section, impeller, and keys (arrange them by number; place a pad in the middle of the pump body) ； ⑩Remove the impeller and partition step by step (make sure to use a pad in between during removal) ； ⑪When it is difficult to remove the impeller, it can be separated by hitting it with a copper rod or a wooden mallet; alternatively, the outside of the impeller can be carefully and evenly heated with a flame ； ⑫After removing the bearing cover, oil slinger, bearings (bushings), oil baffle, and mechanical seal of the inlet section, begin inspecting the components. (2) Inspection and testing of various components: ① Inspection of the shaft – clean it with kerosene and polish it with sandpaper; the surface should be free of any scratches or cracks. Then, use a dial indicator to measure the shaft’s bending degree, which should not exceed 0.05 mm. If this limit is exceeded, the shaft needs to be straightened ； ②Inspection of the impeller: When the impeller is worn and the values exceed those specified in the diagram below, it is necessary to replace the mouth ring. If the fit between the impeller and the shaft is loose, chromium plating can be applied to the inner hole of the impeller; after plating, grinding is carried out, and the clearances between the mouth ring and the inter-stage sleeves are measured step by step. The allowable clearance ranges are as follows: Mouth ring diameter – Standard clearance, Replacement clearance; Inter-stage sleeve replacement clearance: For cold oil pumps, <1000: 0.4–0.6, 1.2–0.3, 0.3–0.4, 0.8; >1000: 0.6–0.8, 1.5, 0.4–0.5, 0.9. For hot oil pumps, <1000: 0.6–0.8, 1.3, 0.4–0.6, 1.0; >1000: 0.8–1.2, 1.6, 0.6–0.5, 1.1. ③ After adjusting the clearances between the mouth ring and the inter-stage sleeves, the rotor is assembled and placed on the bearing frame. A dial indicator is used to measure the runout of the mouth ring and inter-stage sleeves, as well as the runout of the balance disc’s end face. Radial and end-face runout of the rotor can cause uneven wear and vibration; the allowable values for such runout are as follows: For multi-stage centrifugal pumps, allowable radial and end-face runout values – Measurement location, Diameter, Radial runout, End-face runout: Impeller mouth ring, Inter-stage sleeves, Balance disc, Impeller end face: <500: 0.06, 0.03, 0.04, 0.20; 50–1200: 0.08, 0.04; 120–2600: 0.10, 0.05; >2600: 0.12, 0.06. There are many factors that can affect the radial and end-face runout of the rotor, such as bending of the shaft itself, or when the contact surfaces of the rotor’s components are not perpendicular to the shaft’s centerline. Tightening the shaft sleeves may also cause new bending in the shaft. Additionally, insufficient precision in component manufacturing or a loose fit between rotating components and the shaft can lead to deviations in radial and end-face runout. If the excessive runout is caused by shaft bending, the shaft should be straightened first; if it is caused by the end face, the high points on that end face should be identified and the relevant end face areas should be ground. ① To check the clearance at the flange joints of the centrifugal pump casing, there are flange fits between adjacent partitions as well as between the casing components. If this clearance is too large, it will affect the concentricity of the pump’s rotor and stator; therefore, it must be corrected. To determine the clearance between two pump casings, place the adjacent casings one on top of the other, position the dial gauge on top with its contacts in contact with the outer surface of the lower casing, and then move it back and forth in the direction of the pointer. The difference shown on the dial gauge represents the clearance at the flange joints ； Measure again at a position 90°C apart; generally, the shoulder clearance should be between 0.04–0.08 mm. If the clearance is greater than 0.10–0.12 mm, repair is necessary. Measure the clearance of the impeller within the guide vanes (generally, the clearance in shielded pumps or pumps with low flow rates is 3 mm, while for pumps with high flow rates it is 6.4–10 mm). (3) Assembly of multi-stage centrifugal pumps: ① Start the installation after preparing all the components of the pump. Begin from the inlet section, fit the shafts in place and tighten the nuts. The assembly sequence is the reverse of the disassembly sequence; be careful to apply adhesive properly where inter-stage gaskets are used. Lubricant should be applied to mating surfaces such as the ring gaskets during assembly ； ②When assembling, position the components according to the marks made during disassembly. Be careful not to loosen the partitions during assembly, and ensure that the intermediate padding is in place ； Measure the shift amount after each level is installed, and detect and adjust any abnormalities promptly. ③When tightening the bolts, pay attention to symmetry and evenness; it is generally necessary to tighten them in several stages to ensure even tightening ； ④To measure the total play, first avoid using a balance disc and instead use a shaft sleeve; then lock the rotor, push it to one end to take a measurement, and pull it to the other end to take another measurement. The difference between these two values is the total play, which is generally between 6-10 mm ； ⑤Measure the half stroke amount; install the balance disc on the locked rotor, and using the same method, the difference between the two values gives the half stroke amount, which is generally half of the total stroke amount ； Adjustments are made when the standards are not met: For ordinary multi-stage pumps, the size of the balance sleeve can be adjusted; for TDF-type pumps (Calit), the thickness of the gasket behind the balance disc can be adjusted to make the necessary changes ； ⑥Adjust the half-piercing amount and install the end cover, making sure to tighten it evenly. If the support bearings are sliding bearings, it is necessary to measure the amount of lift of the rotor. The method is as follows: Place a dial indicator vertically on the shaft journal; lifting the rotor before installing the support bearings gives the total lift amount. Use the same method to measure the total lift amount at the other end. Once the lower bearing shells at both ends have been installed, measure the lift amounts at those ends again; this value represents the half of the total lift amount. Adjust the set screws beneath the bracket so that the half of the total lift amount plus 0.05 mm is achieved. When making adjustments, be sure to adjust the set screws at both ends as well, and align the bearing housing in the middle position. ⑦When installing the mechanical seal, pay attention to aligning the keyway when fitting the shaft sleeve. The measurement method is as follows: Pull out the rotor, measure the distance from the sealing surface of the rotating ring to the edge of the sealing chamber, and then measure the distance from the sealing surface of the stationary ring to the gasket. The difference between these two distances, minus half of the axial movement, gives the actual compression amount ； For the TDF type, it is sufficient to directly measure by having the balance plate of the balance disc in contact. ⑧Install the bearing housing and bearings to position the rotor; depending on the structural design, there are several types: A. When the bearings are cylindrical roller bearings, it is sufficient to adjust the half-shifting amount, with the axial force being entirely balanced by the balance disc ； B. When the bearings are paired angular contact ball bearings, accurate measurement is necessary: pull the rotor to the outlet end and measure the distance from the step where the outer ring of the bearing makes contact to the step where the inner ring of the bearing makes contact; the latter should be (half the shaft runout – 0.1) mm higher than the former ； C. When the supporting bearings are sliding bearings, part of the axial force is balanced by the balance disc, while the remaining axial force is balanced by the thrust bearing at the rear end. The rotor is pushed forward until the balance disc comes into contact with the balance plate. A dial indicator is placed on the shaft end face, the thrust bearing and lock nut are installed, and the nut is tightened. After it is secured, the rotor is moved forward using a crowbar until it presses against the thrust bearing at the front end. The reading on the dial indicator indicates the clearance of the balance disc; adjustments can be made by adjusting the shims inside the thrust bearing. ⑨ Install bearings, oil rings, nuts, etc., add lubricating oil, and connect the auxiliary pipelines.