Tips for overhauling York screw compressors

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A necessary part of the major overhaul of York screw compressors is the maintenance work on the compressors themselves. Inspection should be carried out in conjunction with the part removal process. In particular, the clearance between the various moving parts that fit together can become worn due to operation – whether due to normal wear or abnormal wear. It is necessary to measure this clearance whenever the components are disassembled; any issues identified must have their causes determined, and the normal clearance should be restored by repairing or replacing the relevant parts. 1. Inspection and repair of the screw-type refrigeration compressor casing and slide valve. (1) Check the inner diameter of the cylinder. ①Use an inner diameter gauge to check the wear of the cylinder bore, measuring at the compression and exhaust ends as well as the slide valve. ②Check the inner diameter of the cylinder and the surface of the spool for any scratches. ③Use a feeler gauge to measure the gap between the male and female rotors and the inner diameter of the cylinder (do this before lifting the male and female rotors out of the cylinder). (2) Cylinder block and spool valve repair. ①Body: If there are very minor wear spots on the inner surface of the cylinder or light scuffing caused by dirt, use an oilstone or an oil-polishing half-round file to polish it in a circular motion. At the same time, the friction area between the male and female rotors also needs to be polished. If the inner surface of the cylinder block is worn beyond 0.6 millimeters and there is severe pitting, the cylinder block should be replaced. ②Spool valve: When there is slight roughness on the surface and minor localized wear, polish it using a semi-circular emery stone or fine sandpaper (240#–280#). If there is severe pitting or wear, the spool valve should be replaced. Additionally, any roughness on the slide track at the lower part of the slide valve should also be polished with fine sandpaper, to prevent issues with normal loading and unloading. 2. Inspection and repair of the female and male rotors in screw-type refrigeration compressors. (1) Inspection of the male and female rotors: ① Use an outer diameter micrometer to measure the outer diameter and shaft diameter of the rotors, and check for wear on the surfaces of the rotors and shafts. ②Check the axial clearance at the rotor end face. The suction end face is measured with a depth micrometer or an oil gauge caliper before the cylinder block is removed. After removing the cylinder block at the exhaust side, use a feeler gauge to measure the gap between the rotor end face and the end cover. ③Check for wear or scratches between the rotor end face and the end faces of the suction and discharge gland plates. (2) Repair of the male and female rotors. If the contact surface between the male and female rotors is uneven, or if there are hard spots or scratches, it can be polished using an oilstone or an oil-polishing file, followed by finishing with fine sandpaper. If there is friction between the rotor and the lower part of the cylinder block as well as the slide valve surface, the wear of the main bearings should be checked first, in order to determine the method for repairing the rotor and the inner surface of the cylinder block. Otherwise, the gap will be too large, resulting in high leakage, reduced cooling capacity, and increased power consumption. The surface of the shaft diameter and the surface at the shaft seal must be free from defects such as rust spots or severe roughness; minor roughness can be smoothed out using 240#–280# fine sandpaper. The degree of wear should be measured in order to determine the fit clearance of the sliding bearings. ? 3. Inspection and repair of the main bearings of screw-type refrigeration compressors. (1) Inspection and measurement of the main bearings. After removing the end cover of the main bearing, measure the inner diameter using an inner diameter gauge. If the wear is not severe, it may not need to be removed. 2) Main bearing repair: ① The main bearing has slight scuffing, but the degree of wear is within the specified limits; the scuffing and fine sand particles can be gently removed using a triangular scraper. ②If the main bearing exceeds its wear limits and the clearance between the components is too large, causing friction between the lower part of the rotor and the cylinder block, the bearing must be replaced. The newly replaced bearings should be scraped at the bottom using a triangular scraper to ensure that the fit meets the required clearance; they should also rotate smoothly on the shaft diameter with a uniform contact surface. ③When assembled onto the end cap, the direction and position of oil supply must not be incorrect. 4. Inspection of the thrust bearings in screw-type refrigeration compressors: (1) Check the surface finish and wear condition of the thrust bearing races as well as the balls or rollers. If the surface appears dull, the bearing clamps are loose, or the bearing clearance exceeds the allowable limits, the bearings should be replaced. (2) Points to note when reassembling or replacing bearings with new ones: ① If the bearing cannot rotate after the fasteners are used to tighten it onto the shaft, the cause must be identified and addressed before attempting to reassemble it. Otherwise, the bearing will be damaged. ②When replacing a new bearing, it is necessary to measure the height difference between the inner and outer rings of the old and new bearings. Based on these measurements, the gap between the end face of the discharge end seat and the end faces of the male and female rotors should be adjusted. This is a very important step. If not adjusted properly, an excessive gap will cause severe steam leakage at the end face, while too small a gap will accelerate wear of the end face. 5. Inspection and repair of the shaft seal of screw-type refrigeration compressors (1) Inspect the shaft seal. Check whether the friction surfaces of the moving ring and stationary ring of the shaft seal are worn or abraded, and also examine whether the rubber sealing ring is aged or whether the spring force of the retaining ring or small spring is insufficient. (2) Shaft seal repair. The repair of the moving ring and the stationary ring is mainly carried out by grinding with abrasive sand, and the grinding methods and requirements are the same as those for pistons. If the rubber ring ages, it should be replaced; if the spring lacks sufficient elasticity, the method of comparing the free height on a glass plate using both a new and an old spring can be used to determine whether replacement is necessary. 6. Inspection of the oil piston in screw-type refrigeration compressors. Check whether the rubber seal of the oil piston meets the requirements; if it has aged, it should be replaced with a new one. Use an inner diameter gauge to check for wear on the inner diameter of the cylinder; if it exceeds the limit value, a new part should be replaced. 7. Inspection of the balance piston and balance cylinder liner of the screw-type refrigeration compressor. The inspection and measurement of the balance piston can be carried out using an outer diameter micrometer. The wear of the balance cylinder can be measured using an inner diameter gauge; if the wear on both sides exceeds the specified limit, it should be replaced with a new part. But as long as there is no lack of lubricant, the amount of wear is very small. 8. Inspection and maintenance of the check valve in screw refrigeration compressors. The suction and exhaust check valves installed on the unit should be regularly inspected for their packing seals, springs, screws, etc.; any damaged or worn-out seals should be replaced with new ones. 9. For screw-type refrigeration compressors, check the energy indicator assembly. If the spring’s elasticity is insufficient, the spring can be replaced; if there are burrs on the pointer sensor, they can be polished with fine sandpaper, and so on. These are some minor details regarding the major repairs of York screw compressors, compiled based on personal experience. I hope that if there is anything incorrect or if anyone has any doubts, they can share them in the form of comments. Thank you all.