Maintenance and installation of piston compressors

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This post was last edited by tanhua on 2010-2-8 22:12. 7. Maintenance and Installation of Piston Compressors 7.1 General Disassembly Procedures and Basic Requirements 1. When disassembling, it is necessary to follow the appropriate procedure based on the compressor’s structure, working from the outside in and from top to bottom. Random disassembly or forceful handling must be avoided to prevent damage or deformation of the components. 2. Try to use specialized tools for disassembly to ensure that the components are not damaged. If the small-end bearing of the connecting rod needs to be removed, it should be pressed out using a press or pulled out with special tools; hammering is not allowed ； To remove the valve assembly, use specialized tools; do not try to remove it by clamping the valve in a vise, as this will cause the valve seat components to become deformed due to the clamping force ； For the connection bolts of the cylinder, piston, and piston rod, special socket wrenches must be used; it is not allowed to use pipe wrenches to clamp directly on the nut or piston rod in order to remove them. 3. When removing components from large compressors, lifting equipment should be used, and the components must be securely fastened, lifted carefully, placed steadily, and supported properly. 4. The removed components should be cleaned thoroughly in accordance with the requirements for clean and orderly maintenance, arranged neatly in order, and covered properly to keep them secure ； Important components should be placed on dedicated racks, precision parts need to be stored carefully, and relevant mating parts should have their assembly positions marked; some of them should also be threaded together or wrapped up to prevent disorder and incorrect installation, which could affect the quality of assembly. 7.2 The disassembly and cleaning of compressors shall be carried out upon request. (1) Compressors that are installed as a whole generally require the following disassembly and cleaning procedures ； 1. For reciprocating piston compressors, the pistons, connecting rods, air valves, and packing should be removed, and the surface of the equipment as well as the removed parts should be cleaned thoroughly. Air valves and packing should not be cleaned with steam ； 2. For reciprocating piston compressors sealed with oil seals, when installed within the oil seal lifespan specified in the equipment’s technical documents, all components except the degassing valve need not be disassembled or cleaned. 3. Screw compressors and vane compressors, when installed within the oil seal lifespan specified in the equipment’s technical documents. It does not require disassembly for cleaning; those with special requirements should follow the provisions in the equipment’s technical documentation ； 4. The diaphragm compressor should have its cover, diaphragm, and suction and exhaust valves removed and cleaned. (II) For compressors assembled on-site, the main units, components, and auxiliary equipment should be cleaned. Valve elements, packing, and other seals should not be cleaned with steam; after cleaning, any residual cleaning agents or moisture must be removed. It is also necessary to check for any damages or defects on the surfaces of the components and equipment. Once everything is in order, a thin layer of lubricant should be applied (components that come into contact with the medium in lubrication-free compressors should not be oiled). 7.3 General requirements for compressor assembly: For compressor assembly, relevant assemblies are typically installed first, followed by the overall assembly. Compressors that require maintenance differ from newly manufactured compressors in terms of assembly. To fully utilize the functionality of the existing components, the gaps between these components and their fit together are not required to be as precise as those for new components; in some cases, it is acceptable for these gaps to be slightly larger or smaller than specified, or even to exceed the prescribed limits. To more effectively eliminate errors during machining and cumulative errors during assembly, it is necessary to carry out manual operations such as filing, scraping, and grinding carefully, in order to ensure the geometric accuracy and fit requirements of the assembly. For example, the fit between the bearing shell and the shaft journal must be improved through lapping to achieve good contact ； Removing defects such as burrs, scratches, and marks from parts can improve assembly quality and precision. In addition, the following points should also be noted: 1. Each newly replaced component must be inspected and tested before installation, and it may only be installed if it meets the requirements. 2. The components should be assembled according to the diagram and the procedure; the assembly procedure is the reverse of the disassembly process. The assembly work must be carried out carefully in accordance with the technical requirements; nothing must be omitted or installed incorrectly ； Identical parts should be assembled according to the markings ； Be careful to prevent foreign objects from falling into the cylinders, the engine block, and the intake and exhaust pipes. 3. An appropriate amount of lubricating oil should be applied to the smooth surfaces of moving parts during assembly. For example, an appropriate amount of lubricant must be applied when the crosshead pin and bushing, piston, piston rings, and piston rod are installed in the cylinder. 4. After each assembly is completed, it must be tested to ensure it meets the requirements. For example, after the piston rod and piston are assembled, their coaxiality needs to be measured ； The parts of some assemblies must pass preliminary inspections before they can be assembled; for example, piston rings must first pass tests for leaks and clearance before they can be installed on the piston. 5. When tightening the bolts that secure various components, in addition to ensuring that the size of the wrench handle matches that of the nut, appropriate force must also be applied. Different torques should be used depending on the diameter of the bolt; applying too much force increases the pre-stress on the bolt, increasing the risk of fatigue fracture ； If the force applied is too low, the tension will be insufficient, leading to loosening as well as vibration or air leakage. When tightening multiple bolts in the same group, it should be done symmetrically and evenly, and the gaps between the components being tightened should be checked regularly to ensure they are compressed uniformly. If a deviation is found in the gap, it should be disassembled for inspection; once the abnormality is resolved, it should be tightened again. Adjustment must not be made by applying different tightening forces to the bolts. 6. The assembled components must be kept clean; no foreign objects are allowed to enter the bearings, cylinders, gaps, packing, or inlet and outlet pipes. 7.4 Installation requirements for the engine block: 1. Before the engine block or crankcase is placed in position, it should be coated with chalk on the outside and kerosene on the inside to conduct a leak test; no leaks after 8 hours indicate that the test is successful, after which the coating should be removed completely ； When cleaning the intermediate body, it is necessary to clean the lubrication oil circuit thoroughly to ensure its smooth flow. 2. Whether shims are used or not, the grid structure at the bottom of the fuselage must be filled with cement mortar at the time of installation; it must not be left suspended. 3. When the machine body is in place, its main shaft and the axis of the middle slide track should coincide with the center line of the foundation; the allowable deviation is 5 mm, while the allowable deviation for elevation is ±5 mm. 4. The lateral and axial levelness of the horizontal compressor body and the middle section should be measured at the sliding guides of the middle section and the bearing seat holes respectively; the values from both ends shall be used as the reference, with the intermediate value serving only as a reference ； The deviation in levelness for both shall not exceed 0.05 mm/m. The tendency of the column to tilt horizontally means that, within the allowable deviation range, the M-shaped frame should be positioned higher on the side of the motor ； The overall structure of the H-shaped compressor spindle system (such as H22) should have the inner bearing seat holes on both sides in the vertical direction ； The motor is equipped with dual **bearings, which should be located in the bearing hole openings on the outside of the two machine housings. 5. For twin-screw, two-casing compressors, the coaxiality deviation of the main bearing hole axes must not exceed 0.03 mm, and it is necessary to maintain a constant axial levelness of the casings. 6. The alignment and leveling of the vertical compressor casing should be carried out by making measurements at the junction surfaces between the casing and the middle section, between the casing and the cylinders, and between the middle section and the cylinders ； For multi-stage cylinders in units that are cast as one with the fuselage, measurements can be taken at the joint surfaces between the cylinders. The longitudinal and lateral levelness deviations of the fuselage shall not exceed 0.05 mm/m. 7. When aligning the L-shaped compressor frame, the levelness of the horizontal rows of the frame can be measured on the frame slides, with the allowable deviation in levelness not exceeding 0.05 mm/m ； Its levelness tendency should be towards the cylinder head end. The axial levelness of the horizontal column fuselage can be measured at the fuselage bearing holes or by using a gauge between the two bearing holes, with the allowable deviation in levelness not exceeding 0.05 mm/m ； The inclination of levelness should be towards the motor end. The levelness of the vertical column frame can be measured at the joint surface where the frame meets the cylinder (using a gauge block and a straight edge) or on the frame slideway, with the allowable deviation in levelness not exceeding 0.05 mm/m. 8. For the alignment and leveling of the double L-type compressor housings, in addition to complying with the regulations for L-type compressors, it is also necessary to first align and level the motor; using the motor as a reference, the high-pressure and low-pressure compressor housings are installed on either side of it. The axial levelness tendency of the fuselage should be high toward the outer bearing seat holes of both fuselages. 9. The deviation in the parallelism of the axes of various columns in a multi-column compressor shall not exceed 0.10 mm/m. 10. When tightening the foot bolts, the levelness of the fuselage and the fit between the crossbeams and the fuselage should not change ； The length of the bolt protruding from the nut should be more than 1.5 times the length of the bolt itself. 7.5 Assembly of the crankshaft and main bearing shells 1. Before assembly, use compressed air to blow out the oil holes in the crankshaft and main bearing shells, and clean them to ensure that the oil passages are unobstructed and the surfaces are clean. 2. The tightening device for the crankshaft and balance weights must be tightened securely. 3. The inner and outer surfaces of the spindle bearing shells should be smooth, and their mating surfaces should be flat; there should be no defects such as cracks, pores, scratches, dents, compressions, or inclusions. 4. After the bolts securing the bearing housing hole are tightened, the fit between the back of the bearing shell and the inner bore of the bearing housing should be no less than 85% of the area of the back surface when the outer diameter D of the bearing shell is ≤ 200 mm ； When D > 200 mm, it should not be less than 70% of the backing area ； If there are areas that do not fit properly, they should be distributed unevenly, and the largest concentrated area should not exceed 10% of the backing area; it is considered acceptable if a feeler gauge of 0.02 mm cannot be inserted into that area. 5. The non-working surface of the tile back should have a coating; the coating must be even, with no bumps or irregularities. The inner surface of the bearing alloy should not be scraped; if there is poor contact with the shaft journal, only minor scraping is allowed, with a scraping amount generally ranging from 0.04 to 0.08 mm. 6. The babbitt layer of the shaft bearing (lower shaft bearing) after grinding should have more than 2/3 of its arc length in contact with the crank journal, with 2–5 contact points per cm². During trimming, the crankshaft should be at the same level as the crankcase ； It is also necessary to regularly use a feeler gauge to check the clearance at the four corners of the fit between the bearing shells and the shaft journals; the deviation of this clearance value must not exceed 0.04 mm, in order to ensure that the center line of the main bearing shell is coaxial with the center line of the crankshaft. 7. The radial clearance between the crankshaft (main shaft) bearing shells and the main shaft journal shall comply with the specifications in Table 1--1. The method of adding or removing shims at the tile joints is commonly used to ensure that each tile has the desired gap ； The measurement of gaps is commonly done using the lead pressure method or feeler gauge testing, with the latter giving a value that is about 0.02 mm lower than the actual gap size. The lateral clearance of the tile joint is half that of the vertical clearance, and the unevenness shall not exceed 0.02 mm. Table 1--1 Radial clearance between the spindle bearing and the journal (unit: mm) Bearing material: Lead-based alloy and tin-based alloy; Copper-based alloy; Aluminum-based alloy; Antimony-magnesium alloy. Radial clearance: (0.0005～0.00075)D, (0.00075～0.001)D, (0.001～0.00125)D, (0.0012～0.0015)D. Note: 1. D in the table refers to the diameter of the spindle or crankpin journal, in mm ； 2. The larger value shall be adopted for those with a larger journal diameter. 8. After placing semi-circular copper rings on both sides of the spindle that is equipped with axial positioning, the axial positioning clearances on both sides should be equal; these clearances should be selected within the range of 0.20~0.50 mm. 9. After the main shaft bearings have been repaired and polished, the coaxiality between the crankshaft centerline and the frame centerline should be checked in both horizontal and vertical directions. A level is commonly used to determine the horizontal deviation of the crankshaft centerline with respect to the vertical direction of the aircraft fuselage centerline; the levelness of the crankshaft journals should differ from that of the bearing holes in the housing by less than 0.02 mm/m ； In the horizontal direction, a scale can be used to measure the distance between the crank and the end face of the bearing hole in the housing; the difference in this distance between the left and right sides should not exceed 0.01 mm/m. 10. The tightening torque of the bearing housing bolts and the elongation after tightening shall meet the specified requirements. 11. After the crankshaft is installed, position the crank pin at 0°, 90°, 180°, and 270°, and use an inner diameter micrometer to measure the distance between adjacent crank arms; the deviation shall not exceed 10% of the piston stroke value. Check the parallelism of the crank journal to the main journal at four positions perpendicular to each other; the deviation shall not exceed 0.15 mm/m. 12. After the bearing shells have been properly installed, it is also necessary to check the difference between each crank throw of the crankshaft; this difference should not exceed 0.02 mm/100 mm. 13. After the above steps are completed, lift the crankshaft to remove the main bearing shells, and thoroughly clean the crankshaft, main bearing shells, engine block bearing seats, and bearing caps among other components ； Place the lower bearings for each main shaft and the crankshaft in their respective marked positions, and install the shims on both sides of the bearing seats ； Apply an appropriate amount of lubricant to each journal ； Place the upper half-shells of each main shaft in their corresponding positions; after adjusting the shelling gaskets, cover each shell with its corresponding cover ； Tighten the bolts of the main shaft bearing shells, tightening them evenly in a cross pattern to the specified torque ； Measure the gap between the tiles to ensure it meets the specified requirements, and finally install the locknut or other anti-loosening devices. After the crankshaft and main bearing shells have been assembled, rotate the crankshaft and check by feel to ensure that the assembly is correct ； If there is a feeling of friction, it should be disassembled for inspection; after the issue is resolved, it should be reassembled and tested. 7.6 Cylinder Installation 1. Pre-installation Inspection A thorough inspection should be carried out before installation; a hydrostatic test should be conducted for everything that is not specified otherwise (including the cylinder and its water jacket) ； The connection surfaces between the cylinder block and the intermediate section, as well as the contact surfaces between the cylinder valve chamber and the valve seat, should be free from any mechanical damage or defects; the cylinder surfaces must not have cracks, porosity, or other such defects ； The cylindricity of the working surfaces of each cylinder level is measured using an inner diameter micrometer, and the deviation must not be greater than the tolerance value for grade 8 per the standards. 2. Installation requirements for horizontal compressor cylinders: (1) When connecting the cylinder to the middle body, the connection bolts should be tightened symmetrically and evenly; the cylinder supports must make good contact with the cylinder’s support surfaces, and the load should be distributed evenly. (2) When using the wire-tensioning method to align the coaxiality of the cylinder axis and the middle body slide axis, the following requirements must be met: the deviation in coaxiality between the cylinder axis and the middle body slide axis shall comply with the specifications given in Table 1--2. If the specified limit is exceeded, the cylinder should be displaced horizontally or radially, or the mating fit should be adjusted by scraping; adjusting it by using shims or applying external force is not permitted. . The contact area of the treated shoulder surface should be over 60%. Adjust the levelness of the cylinders; the deviation shall not exceed 0.05 mm/m, and the direction of inclination should be consistent with that of the middle section (towards the cylinder head at the higher end), but it must comply with the specifications in Table 1--2. The coaxiality deviation between the axis of the packing seat and the axis of the cylinder should also meet the aforementioned requirements. Table 1–2: Deviation in coaxiality between the cylinder axis and the axis of the crosshead slide in the middle block. Cylinder diameter/mm, Radial displacement/mm, Axial tilt/mm: ≤100: 100–300; 300–500; 500–1000; >1000: ≤0.05, ≤0.07, ≤0.10, ≤0.15, ≤0.20. ≤0.02, ≤0.02, ≤0.04, ≤0.06, ≤0.08. 3. Installation of vertical compressor cylinders: (1) When connecting the cylinder to the machine frame, or between cylinders, or to the middle block, the bolts should be tightened symmetrically and evenly; the supporting surfaces must make good contact, and the loads should be distributed evenly. (2) The levelness of the cylinder can be measured on the contact surface between the cylinder head and the top dead center of the cylinder ； When the diameter of the working surface of the cylinder is greater than 150 mm, measurement can also be taken on the mirror surface of the cylinder liner. Its levelness deviation shall not exceed 0.05 mm/m. (3) When it is not possible to place a level on the contact surface of the cylinder’s shoulder, gauge blocks and a straight edge can be used to measure the levelness on the straight edge. (4) The coaxiality of the cylinder with the airframe, between cylinders, or with the axis of the central body shall meet the requirements specified in Table 1--2. The contact area between the mating faces should be over 60%. (5) When using a laser collimator to align the coaxiality of the axes of each cylinder with the axis of the central slide, the center of the photoelectric receiving target mounted within the cylinder’s mirror surface should coincide with the cylinder axis. The deviation of the center line of the photoelectric receiving target from the axis of the laser beam shall not be greater than the tolerance value specified in standard grade 9. 7.7 Assembly of the connecting rod assembly 1. Before assembly, the shaft bearings of the crosshead and the connecting rod should be inspected; the alloy layers on the crosshead and those on the large end of the connecting rod must be smooth and intact, without any defects such as cracks, pores, shrinkage, scratches, dents, crushes, or inclusions ； The alloy layer must adhere firmly to the backside ； The oil passages in the connecting rod body and the crosshead should be cleaned and kept unobstructed. 2. The connecting rod cap bearing and the cap bore have an interference fit; when the bearing is inserted into the bore, its inner diameter contracts, and the amount of contraction is generally equal to the degree of interference. Therefore, as the outer diameter of the connecting rod cap bearing increases, its inner diameter must also increase accordingly. The fitting interference of small-head bearings is related to the material and diameter of the bearing; for example, the interference for copper bearings is generally 0.4/1000 to 0.5/1000 of the diameter, with the exact value specified in the drawings. Depending on the size of the head gasket and the assembly conditions, those with an outer diameter of 100 mm or less are generally assembled using the pressing method ； For those with an outer diameter greater than 100 mm, the freezing method can be used if conditions permit; it is convenient and results in good assembly quality. 3. Scraping and lapping of the large-end tile: Scrape and lap the back side of the large-end tile so that the contact area between the mating surfaces is 70%~85% or more ； When scraping the big end bearings of the connecting rod, the scraping must be even; during the scraping process, the wall thickness of the bearings should be checked frequently to ensure that the thickness is equal across the coaxial cross-section, thus maintaining perpendicularity between the bearing and the center line of the connecting rod. The clearance between the large-end tile and the curved neck is adjusted using tile gaskets, which are commonly used for thick-walled tiles ； If the gap in the thin-walled tile is small, it can be appropriately filed; if it is too large, a new tile must be replaced. For the measurement of its clearance, the radial clearance is usually determined using the lead compression method, while the axial clearance is measured with a feeler gauge. Alternatively, the radial clearance can be calculated by subtracting the diameter of the bearing bore from the shaft diameter, and the axial clearance can be obtained by subtracting the length of the shaft diameter from the width of the connecting rod bearing ； Its radial clearance is 0.8/1000 to 1.2/1000 of the bend diameter. 4. Lapping of the small-end bearing and the crosshead pin (or piston pin): After the bearing is pressed into the small-end hole of the connecting rod, there is usually some amount of material left that needs to be ground off. Its scraped surface should be smooth, and the contact points should be evenly distributed. After lapping, the connecting rod cap bushings and the pin shafts should be marked respectively for assembly purposes. During the lapping of the small-end bushing and pin, scraping should be carried out while using measuring tools to check the ends of the bushing, in order to avoid excessive scraping or the formation of an oval or conical shape. The fit clearance between the small-head bearing shell and the pin shaft is related to the material of the bearing shell as well as the diameter of its holes; for example, the fit clearance for copper-lined bearing shells is 0.8/1000 to 1.2/1000 of the hole diameter, while for steel-cased babbitt bearing shells it is 0.4/1000 to 0.8/1000 of the hole diameter. If the gap is too small, the amount of lubricating oil that enters decreases, increasing the risk of bearing burnout ； If the gap is too large, the impact force increases, which can easily cause damage to the bearings; therefore, it is necessary to carry out the fitting process in strict accordance with the technical specifications. The contact area between the crosshead pin or piston pin and the crosshead pin hole or piston pin hole should be no less than 60%; the cylindricity deviation of the working surface of the connecting rod small-end shaft hole must not exceed the tolerance level 7 specified by national standards ； The crosshead pin of the connecting rod small-end bearing should make even contact, with the contact area accounting for over 70%. The axial clearance between the end face of the connecting rod journal bearing and the plane of the inner protrusion in the crosshead pin hole shall meet the technical specifications. 5. Connection between the crosshead and the piston rod: The piston rod should be able to move freely into the hole at the end of the crosshead. When using shims for adjustment, these shims should make even contact with both the bottom surface of the inner hole in the crosshead flange and the rear end surface of the piston rod ； When connected by threads, the end face of the crosshead flange should be fitted and lapped against the contact surface of the lock nut to ensure even contact ； When connected using wedge keys, it is necessary to ensure that the upper and lower surfaces of the key fit tightly with the mating surfaces of the keyway; a feeler gauge should be used to check that the gaps on both sides of the key are equal. 6. Assembly of the connecting rod bolt: The connecting rod bolt is an important component of the compressor; if the tension applied during its assembly is too high, it will result in increased prestress and eventual breakage ； If the tension is too low, the nut tends to loosen, leading to increased wear of the bolt. Medium and small connecting rod bolts can be handled using a torque wrench ； For large connecting rod bolts, the tightening force of the assembly bolts can be determined using methods such as the elongation of the bolt under load. The tightening force is proportional to the material strength of the bolt and the bolt diameter. For carbon steel rod bolts, the maximum elongation shall not exceed 0.3/1000 of the total length of the bolt ； For alloy steel connecting rod bolts, the maximum elongation shall not exceed 0.4/1000 of the total length of the bolt. During assembly, the end face of the rod bolt head in contact with the end face of the rod body used for positioning, as well as the contact between the nut and the end face of the rod’s large end cap, should be even ； The fit tolerance grade for the connecting rod bolt and the hole in the connecting rod body is H7/h6 ； When inserting the connecting rod bolt into the hole, push it in with moderate force or tap it into place without being too tight or too loose. 7. Inspection after the assembly of the connecting rod assembly: (1) Inspection of the parallelism between the center line of the bearing hole in the large end of the connecting rod and the center line of the bearing bush in the small end. When the connecting rod is in the vertical position, place two precise standard V-blocks on the flat surface, then place the crankshaft on these V-blocks; first, level the main journal of the crankshaft ； Fasten the big end bearing of the connecting rod that is to be inspected using the connecting rod bolts. Insert a test shaft with a length 2 to 3 times that of the bearing’s width into the hole of the small end bearing; position the neck of this shaft at the lowest point. Measure the test shaft using a dial indicator, taking readings from both the left and right sides of the shaft, and record each reading ； Then, rotate the crankshaft by 180° with the connecting rod still in a vertical position, and take a second measurement using a dial indicator. Record the reading, and calculate the parallelism deviation based on the two readings. Its reading should not exceed 0.02 mm/100 mm ； If it exceeds this value, it indicates that the centerlines of the two holes are tilted or the connecting rod itself is bent, and correction measures should be taken. (2) Inspection of the twist degree between the center line of the big-end bearing hole of the connecting rod and the center line of the small-end bushing. When checking for twist in the large and small ends of the connecting rod, place the crankshaft journal and the connecting rod horizontally on a platform. First, level the crankshaft journal, then use a dial indicator to make measurements on the inspection shaft of the connecting rod’s small-end bearing. If the readings on both sides are identical, there is no twist ； If they are different, the difference represents their distortion value. Its distortion value should not exceed 0.02 mm/100 mm; if it does, the tile should be replaced or the linkage body adjusted. 7.8 Assembly of the crosshead and slide 1. Lapping of the crosshead and slide (1) Measure the outer diameter of the crosshead to be lapped using an outside micrometer, and measure the dimensions of the machine frame slide using an inside micrometer; calculate the amount that needs to be lapped from the crosshead. Generally, a lapping allowance of 0.1~0.2 mm is sufficient. If this allowance is too large, the excess material can be removed by turning the entire crosshead ； Removable crosshead, adjustable using non-working slider shims. (2) During scraping, apply colored oil on the slide surface, insert the crosshead to be polished into the slide, push and pull the crosshead back and forth, and scrape along the colored marks until the fit clearance as well as the contact between the upper and lower slides meet the required standards. (3) When fitting the crosshead to the slide, in addition to scraping and inserting material to measure the clearance, it is also necessary to check the coaxiality between the center line of the crosshead and the center line of the slide. This is done by inserting a piston rod along with a special fixture (a hollow short shaft similar to the piston rod) into the hole in the crosshead’s piston rod, securing the piston rod connector using the crosshead, and then using an inner diameter micrometer to measure the distance from this fixture to the slide at its middle and front sections. If the distances between the symmetric points above and below, as well as to the left and right, at the two cross-sections are equal, then the crosshead and the slideway are coaxial at that point ； If both cross-sections are concentric, the centerline of the crosshead coincides with the centerline of the slide ； Otherwise, the two centerlines are either parallel or skewed. During scraping and lapping, adjustments should be made based on the measured deviation to keep the error within the allowable range. 2. Requirements for the fit between the crosshead and the slideway: (1) After placing the crosshead in the slideway, use a square and feeler gauges to check that the perpendicularity of the crosshead at its front and rear ends, as well as with respect to the upper and lower slideways, meets the specified requirements ； The clearance between the crosshead and the upper and lower guides throughout the entire movement should meet the specified values. If not specified, a value of 0.7‰ to 0.8‰ of the slide diameter (or the outer diameter of the crosshead) can be chosen, or a value corresponding to the tolerance grade H8/h9 can be used. (2) The contact surfaces between the back sides of the upper and lower slides and the crosshead body should be in even contact, covering more than 50%. When scraping is required, the gap between the slider and the slide rail should be regularly measured with a feeler gauge to prevent misalignment during scraping. (3) The crosshead working slide should make even contact with the guide rails, and the contact area should be no less than 80% of the total area of the slide ； The uniform contact area of the non-working skate should not be less than 60%. (4) The fit between the slider and the crosshead is of H7/js6 grade ； During assembly, strike to tighten the fit while using wooden boards as a pad. (5) When adjusting the center or clearance of the crosshead using sliding shims, the thickness of the shims added or removed should be consistent ； A lockout device should be used when tightening the fixing bolts of the detachable crosshead slider. (6) The centerline of the crosshead is allowed to be 0.05~0.10 mm lower than the centerline of the slideway, and the lateral tilt error must not exceed 0.01 mm/200 mm. For the crosshead subjected to forces from the slide rail, its axis should be adjusted to a position 0.03 mm above the axis of the slide rail, in order to account for wear that occurs during operation ； For the crosshead that is subjected to forces on the upper slide, its axis should be adjusted to be below the axis of the slide; the value for this adjustment is the gap between the crosshead and the slide plus 0.03 mm ； The crosshead as a whole is manufactured with its axis offset upward or downward by a certain amount at the time of production; therefore, during installation, the crosshead with an upwardly offset axis should be installed on the side of the lower slide that is under stress, while the one with a downwardly offset axis should be installed on the side of the upper slide that is under stress. 7.9 Assembly of the packing box 1. Tri-lobed or hex-lobed flat packings (commonly used for medium and low pressure sealing) and tapered packings (commonly used for high and medium pressure sealing) are often used together in a single compression unit. Before installation, both the oil scraper and the stuffing box should be disassembled for cleaning, inspection, and lapping, with marks made on the non-working surfaces to prevent confusion and incorrect assembly. During assembly, compressed air should be used to clean out all oil, water, and gas passages as well as the holes for positioning pins, to ensure unobstructed flow ； The positioning pin holes, oil holes, and exhaust holes should be aligned separately and assembled according to the designated numbers; the openings of the rings should be offset from each other as required ； The edge of the oil scraper should not be rounded, and its orientation must not be reversed. 2. The end faces of each packing box should be ground on a flat surface; the two conical sealing surfaces of the conical metal packing seals, the end face of the metal flat packing seal, and the contact surface with the piston rod should all be fitted precisely, with the total area of these contact points accounting for 70%~80% or more of the sealing area. The sealing end face of the plastic packing should be polished smooth with fine sandpaper; as for the inner cylindrical surface in contact with the piston rod, it only needs to be checked to ensure that it fits closely against the piston rod. 3. When checking and adjusting the assembly clearance of the packing box, special attention should be paid to the parallelism of the two end surfaces of the packing as well as their perpendicularity to the shaft hole. 4. The oil holes and cooling water holes that connect the various filler boxes must be aligned properly to ensure unobstructed flow. The order of assembling sealing components such as the locking ring and seal ring inside the plastic flat packing box must not be reversed (the locking ring should be positioned closer to the cylinder, with the seal ring on the outside, followed by the flow-blocking ring); the installation order of other packing materials must also be correct. The inner circles of the two end faces where the sealing ring and the retaining ring fit together must not be chamfered or rounded; otherwise, sealing will not be achieved. 5. In oil-free or low-oil lubrication compressors, the non-metallic packing shall have no defects such as scratches or gouges on the end faces of its rings, the inner surface, and the cut surfaces ； The axial and radial clearances between the packing ring and the packing box shall comply with the specifications in Table 1--3 ； It is an open-plan non-metallic sealing ring with metal bands; the lengths of the springs compressed against the outer circular surface of these metal bands should be equal, and the elastic force should be uniform. Tables 1–3: Axial and radial clearances between the packing ring and the packing box. Material of the packing ring: Axial clearance/mm, Radial clearance/mm. Cast iron packing box, Copper packing box, PTFE-filled, Metal/PTFE. 0.432–0.533, 0.279–0.381; 0.508–0.584, 0.365–0.457. 1.524, 1.524, 7.10. Assembly of intake and exhaust valves: 1. Before installation, inspect components such as valve discs, valve seats, lift limiters, valve springs, and bolts to ensure there are no defects such as burrs, scratches, cracks, or warping ； Inspect the contact surface between the valve disc and the valve seat by coloring; they should fit tightly together, with a warping degree generally not exceeding 0.03 mm. If the contact is poor, place the valve disc on the valve seat and grind it there ； When testing the spring force of the valve spring by hand, the spring force within the same group of valves should be consistent ； Clean all parts to be installed with kerosene and wipe them dry; no foreign objects are allowed to be present. 2. Assembly of ring valves and mesh valves: (1) Place the valve seat flat on a special fixture to prevent it from rotating, and position the valve disc in the correct location on the valve seat ； The flatness deviation of the annular valve disc shall comply with the specifications in Table 1--4. Tables 1–4: Flatness deviation of ring-shaped valve discs (unit: mm). Valve disc thickness δ; Valve disc outer diameter: D ≤65, >65~140, >140~200, >200~300. Flatness deviation values: >1.5, 0.04, 0.06, 0.09, 0.12; ≤1.5, 0.08, 0.12, 0.18, 0.24. (2) For each valve disc in a pneumatic cushion valve, the fit with the buffer groove is such that the inner diameter is (H8, H9)/f9, and the outer diameter is (H8, H9)/e8. During installation, it should be ensured that the valve disc falls freely into the buffer groove and can rotate smoothly along the circumference of the groove ； The depth of the buffer tank should preferably be greater than the thickness of the valve disc to achieve a better buffering effect. The valve disc of the air cushion valve is placed on a spring in its free state; it is difficult to assemble the valve when the disc is not yet inside the buffer groove. To address this, several copper sheets with a thickness of 2 mm can be placed along the radius of the valve to press the disc into the groove in advance, and these copper sheets can then be removed once the valve seat and the lift limiter come together. (3) When assembling the air valve, the spring is placed on the valve disc at the position of the lift limiter spring hole ； Then insert the lift limiter into the bolt and align it with the spring; it must not be tilted ； Tighten the nut. (4) After the air valve is assembled, there should be no sticking or deviation when the valve disc and spring move ； The opening height of the gas valve is high, generally ranging from 2.2 to 2.6 mm. (5) After the air valve is assembled, a leak test using kerosene should be conducted; there should be no continuous dripping leakage within 5 minutes, and the number of drops must not exceed the values specified in Table 1–5. Tables 1–5: Number of leakage drops, Number of valve disc rings: 1, 2, 3, 4. Number of leakage drops/5 min: ≤10, ≤28, ≤40, ≤64. (6) After tightening the central connecting bolts and nuts of the valve, they should be secured firmly or riveted in place ； Both the set screws and locking devices should be tightened securely. (7) The gaskets used during assembly should be flat, free from defects such as cracks or scratches ； The size of the valve flange gasket used should be suitable for the flange size. (8) The intake and exhaust valves must not be installed in reverse ； The valve assembly can also be left out before the no-load test run, with only the valve gland installed to prevent oil splashing.