Could you please discuss the clearance between the various components of a reciprocating compressor as well as the key points to consider during installation?

We overhauled a reciprocating compressor: 10 air valves were replaced, and the clearances of the main thrust bearings were measured. The difference between the upper and lower clearances was too large, so the piston had to be removed; thereafter the thrust bearings and their piston rings were replaced. During installation, the dead-center clearance of the piston stroke was also measured. Since it was a medium-level overhaul, the crankshaft was not disassembled, so we are not aware of anything else

There is more compression for the clearance to be measured. The fit clearance of the bearing shells, large-end shells, and small-end shells as well as the clamping force on the back of these shells, as well as the fit clearance between the crosshead and the pin. The tension of the crankshaft. Gap in the upper track. The vertical and horizontal runout values of the piston rod. Clearances at the dead centers before and after operation, opening clearances of the piston ring support rings, radial clearances with the cylinder liner, and axial clearances with the piston groove. Axial gap between packing seals, radial gap with the packing box, and gap at the packing ring cut. Radial clearance between the oil scrapper ring and the piston rod. As for the main points during installation, in addition to carrying out the necessary inspection procedures, it is also necessary to check the alignment of the motor with the wheel set. The levelness and alignment of the cylinder banks, whether the oil circuits are clean and unobstructed, there is no sticking or uneven loading when turning the engine, and all levels of gas valves pass leak tests properly. That’s all I can recall; more details can be added downstairs.

Choosing the right compressor lubricant is an important way to save energy and reduce operating costs. The proper selection of lubricating oil has an impact on the operating costs of compressors. Through experiments conducted by Xi’an Jiaotong University, it was shown that, under identical test conditions on compressors of the same model, using lubricants with a lower viscosity can reduce the specific power consumption of the compressors by up to 100%, without any significant difference in the wear rate of the machine components. The Yaha operation area of the Xinjiang Development Division has imported high-pressure gas compressors driven by 4-stroke engines manufactured by COOPER Company in the United States, of the 16SGT/MH-66 type, in order to achieve pressure-based extraction and thus pursue a long-term, stable, and efficient development strategy as well as to increase the ultimate recovery rate of the gas field. The engine model is 16SGT, with a speed of 600–1200 rpm and a power output of 2650 horsepower. The compressor model is MH-66; it is of a 6-row, 6-cylinder symmetrical balance type. Its stroke is 152.4 mm, the rotation speed is 900 rpm, the diameter of the piston rod is 2.25 inches. The intake pressure ranges from 6.8 to 7.2 MPa, while the designed exhaust pressure is 52/57 MPa; in actual use, it is 46 MPa. The intake temperature lies between 21 and 30°C. It features three stages of compression, with cylinder diameters of φ127, φ107.95, and φ60.325 (corresponding to 5, 4.25, and 2.375 inches respectively). The exhaust temperatures are 90°C, 125°C, and 85°C respectively. The gas supply rate is 45–58×10^4 Nm/h. A total of 7 units of this type are in use in the Yahaa operation area, and significant efforts have been made to reduce the lubricant consumption of these machines. For Unit 2 alone, before adjustments were made, the fuel consumption was 4.8 strokes per minute, resulting in an annual fuel consumption of 11,840 liters and annual costs of 1.25 million yuan. After the adjustments, the fuel consumption dropped to 7,955 liters per year, with annual costs of 840,000 yuan – a savings of 410,000 yuan per unit. With 6 units in operation, the overall annual savings amount to 2.46 million yuan. This compressor uses Mobil HE320 lubricant, with a price of 106 yuan per liter. Due to the high volume of lubricant used and its high cost, lubricant expenses account for 40% of the operating costs of these compressors. A typical example of a lubrication system for reciprocating compressors is an integrated gas engine-compressor unit, where the engine and the compressor share the same casing and crankshaft; its lubrication system utilizes a combination of splash, immersion, and forced oil supply methods. The crankcase splash lubrication system provides adequate lubrication to the main bearings, the big end bearings of the connecting rods, the crosshead pins, the crossheads, the gears driven by the crankshaft, as well as the parallel shaft gears and bearings at the flywheel end. The immersion lubrication system in the control box provides lubrication for gears and similar components. The forced oil injection lubrication system supplies lubricating oil to the power cylinder and compressor cylinders, providing lubrication for the pistons, piston rings, cylinder walls, as well as the compressor’s piston rod and pressure packing. Integrated gas engine–compressor unit, in which the engine is fueled by clean natural gas and the compressor uses natural gas as the working medium; if the natural gas contains components such as H2S and is thus acidic, lubricants containing canola oil must never be used, as this will result in severe gelation deposits. Generally, the power cylinder and crankcase should use lubricating oil of the formulation specified for two-stroke gas engines. Cooper Energy AIX specifies that for non-turbocharged, low-speed, integral natural gas engines – compressor units, the lubricating oil for the power cylinders and crankcase should be of SAE 30# viscosity level as defined by the Society of Automotive Engineers; in addition, it must meet the requirements of API engine oil grades CA and CB. The general technical specifications are shown in Table 1. For engines–compressors, a suitable lubricant is oil that meets the general technical requirements specified in Table 1; however, ash-free additives are generally used, commonly referred to as \"ash-free gas compressor lubricants\", with a sulfate ash content of less than 0.1% according to the A, S, T, M, D874 standards. Lubricants of this type should not contain zinc dithiophosphate in their complete additive formula, where the zinc content by weight exceeds 0.04%. Using engine oil with a high amount of additives accelerates the deposition of ash on the combustion surface. The specified viscosity applies to SAE30# grade lubricating oil, which is suitable for normal conditions. In certain conditions such as starting at low temperatures or operating at very low or very high ambient temperatures, lubricants with viscosity grades other than SAE30# can be used. It must also be noted that before starting the engine, the oil temperature in the crankcase must be higher than the pour point temperature. When the oil temperature is below the pour point, equipment failure can occur due to a lack of lubrication. An oil temperature heating device should be available. The regulations listed above can be applied to lubricants for crankcases. For lubricating oil used in the filling of compressor cylinders and piston rods, the compression medium and exhaust temperature must be taken into consideration. For clean, dry gases with an outlet temperature as high as 300°F (149°C), such as helium and oxygen, a high-quality, solvent-refined pure mineral oil is required to meet the lubrication needs. Air compressors often fail due to hard carbon deposits, as these deposits interfere with the operation of the exhaust valves. This can be mitigated by using so-called naphthenic or low-viscosity-index oils; when the exhaust temperature of the air compressor exceeds 149°C but remains below 176°C, fire hazard exists, and the use of flame-resistant synthetic lubricants is recommended. Non-metallic components of the compressor cylinder should also be considered to ensure compatibility with the selected synthetic lubricant. It must be noted that in certain situations, such as when the oil film on the lubricated surface is washed away by hydrocarbons carried by gases, it is recommended to add 3–5% of a composite oil (i.e., a petroleum-based oil containing acid-free animal fat, vegetable oil, or synthetic fatty oils). Experience has shown that this is a satisfactory measure in some cases. It is to be reiterated that before making a final decision on the lubricant, all operating conditions should be listed and used to consult well-known lubricant manufacturers. These conditions should include cylinder diameter, stroke, speed, pressure, temperature, gas composition, gas purity, as well as the ability of the lubricant to mix with the compressed gas. Attention should also be paid to the materials used for piston rings, piston rods, packing seals, and the cylinder block (or cylinder head). When changing the lubricant grade or manufacturer, do not mix the oil in the filler and crankcase with lubricants of different grades or types. Abroad, for the lubrication of the compressor cylinders and piston rod fillers in integrated gas engine-compressor units, Mobil’s Pegasus 390 or Pegasus 100/30 lubricants are recommended, and the recommended viscosity levels for these oils at various cylinder pressures are listed in Table 2. Here, the reasons for carbon deposition in the integrated gas engine-compressor power cylinder block are outlined again: 1. The lubricating oil does not meet the technical specifications. The specifications require that the sulfate ash content in the lubricating oil for the power cylinders should not exceed 0.1%; however, ordinary users employ CC and VD grade four-stroke turbocharged diesel engines, whose oil has an ash content as high as 1.2–1.5% or more. High levels of carbon cause carbon buildup on the piston rings in the power cylinder and on the spark plugs. 2. Another reason is an excessive amount of oil injected into the power cylinder. It is recommended to use 0.8 pints, or 0.4 liters, of oil per 25 horsepower; for an 800-horsepower engine, 25.6 pints, or 12.1 liters, per day will suffice. Compressor manufacturers cannot test whether the lubricants available on the market are suitable for various gases, so their recommendations can only serve as a reference. In most cases, the lubricant to be used is determined jointly by the compressor manufacturer, the user, and their lubricant supplier. Performance requirements for compressor lubricants: The lubrication of large and medium-sized reciprocating piston compressors needs to be considered in two parts. A circulating oil lubrication system is used for the crankshaft and connecting rod assembly, such as shaft end pump systems; larger compressors employ thin oil stations. The crankcase oil pump supplies oil continuously to the main bearings and rod bearings, as well as to the crosshead pins and crosshead slides, at a pressure of 40–50 PSI (0.276–0.345 MPa). This helps to reduce friction and remove heat, thereby maintaining the oil temperature between 135–160°F (57–71°C) and preventing the formation of water vapor. The pump draws oil from the crankcase, and the oil returns to the main bearing leakage pipes via a thermostatically controlled cooler and filter. Foreign compressor manufacturers generally recommend using lubricating oils with rust and oxidation inhibitors, of grade SAE 30–40. Through research, the oils suitable for the drive mechanisms of various reciprocating compressors in China have been identified, as shown in Table 3. The lubrication of the compressor cylinder and piston rod fillers is different from that in the crankcase, as the lubricating oil does not circulate; proper operation of the cylinder requires a continuous and steady supply of oil to both the cylinder and the piston rod. The diversity of compressed gas media includes air, as well as petroleum gases containing hydrogen sulfide, desulfurized natural gas, cryogenic gases, gases carrying liquid hydrocarbons, and gases carrying water. These gases affect lubrication through mechanisms such as oxidative corrosion, chemical reactions, water washing, dilution, and gas absorption. The compressed gas pressure ranges from vacuum to as high as 6000 PSI (41.3 MPa) or even higher, while the temperature range is from -60°F (-51.1°C) to 400°F (204°C). The materials for piston rings and sealing rings can be metal or non-metal, among others. Therefore, the selection of lubricant for the compressor cylinders should take the above factors fully into account; choosing the right one can extend the lifespan of the friction components. The performance requirements for lubricating oil in compressor cylinders are as follows: 1. The quality of the base oil must be high. The base oils used in compressors fall into two categories: mineral oils and synthetic oils. The production of mineral oil generally involves obtaining a base oil through processes such as refining, degreasing, hydrogenation, or clay treatment, followed by the addition of necessary additives for blending. Synthetic oil is obtained by using chemically synthesized organic liquid base oils, to which the desired additives are then added. Synthetic lubricants used in compressors mainly include diesters, polyethers, synthetic hydrocarbons, fluorosilicone oils, and phosphate esters; as a result, their price is higher than that of mineral oils. The price of synthetic oils is generally 4 to 8 times that of mineral oils. Perfluoroalkyl ethers are up to 500 times that of mineral oil. However, the overall economic benefits of synthetic oils exceed those of conventional mineral oils; their oxidation stability and tendency to form sludge are superior to those of conventional mineral oils. They can be used at higher temperatures and have a longer service life, enabling them to meet usage requirements that conventional mineral oils for compressors cannot satisfy. The base oil in compressors typically accounts for more than 95% of the final oil mixture. The base oil fraction should be narrow: Studies on the operating conditions of compressor oils indicate that improving the composition of the base oil is a key factor in enhancing the quality of compressor oils. After compressor oil composed of light and heavy components is injected into the compressor cylinders, the light component evaporates rapidly and is expelled from the cylinders early, while the heavy component, due to its lower volatility, leaves more slowly. Over time, under the influence of exhaust temperature and oxygen, carbon deposits form. Therefore, a narrow-distillation base oil should be chosen for lubricants. 2. The viscosity should be chosen appropriately. The viscosity of lubricating oil is always selected based on the operating temperature or the maximum exhaust temperature. At the operating temperature, the lubricating oil must have sufficient viscosity to form an oil film that prevents the moving parts from coming into contact with each other, thereby minimizing wear in the system when abrasive particles are present. When selecting lubricating oil, it is necessary to take into account the exhaust temperature of the cylinder as well as the \"cold flow\" temperature; do not confuse the cold flow temperature with the \"pour point\" in the oil’s properties. The cold flow temperature is the temperature at which the oil pump becomes vacuumed or at which the plunger cannot draw in fluid continuously during the suction stroke. Regardless of the lubricant chosen, the cold flow limit occurs in the viscosity range of 6000 to 10000 SUS (Saybolt Universal Viscosity). When the viscosity of the lubricating oil is equal to that of water, the lubricating oil film is unable to withstand dynamic loads, causing the lubricant to fail rapidly; this minimum viscosity is approximately 36 SUS. Through research, lubricants suitable for the cylinder parts of reciprocating compressors in China have been identified, as shown in Table 4. Excessively high viscosity increases fuel and power consumption, and it causes deposits to form at the cylinder valves and in the piston ring grooves. Too low viscosity makes it difficult to form an oil film, which accelerates component wear and shortens their lifespan. 3. Attention should be paid to the absorption of gases by lubricants. All petroleum-based compressors absorb gases. The higher the gas pressure, the more gas is absorbed by the lubricating oil. The viscosity of the lubricating oil decreases after it absorbs gas in the cylinder. The effect of this gas dilution is difficult to measure accurately. Laboratory tests were conducted using natural gas at a pressure of 980 PSI (6.78 MPa), and the results showed that the volume of gas absorbed by one gallon of lubricating oil, in its uncompressed state, was 0.75 gallons (i.e., 3.423 liters). When selecting lubricating oil based on the operating temperature, increasing its viscosity by 5-10 SUS is an effective and feasible method to mitigate this effect to some extent; generally, it is necessary to choose a lubricating oil with a higher SAE grade. 4. Dilution effect of liquid hydrocarbons: Compressors in oil and gas fields are exposed to streams of liquid hydrocarbons. Petroleum-based lubricants are also hydrocarbons, and they can be easily diluted or washed away by liquid hydrocarbons in the air flow. There are three solutions: removing liquid hydrocarbons from the airflow, choosing lubricants with the highest viscosity, and using oil-free designs, in which components such as piston rings, support rings, sealing rings, and valve plates are made of filled polytetrafluoroethylene, carbon fiber, or PEEK. Plastic sealing elements such as polyimides, with low-oil or oil-free lubrication. 5. Lubricant additives: In addition to additives that remove water and wet metals, wear in compressor cylinders is mostly caused by water present in the airflow. When water seeps into the cylinder or is generated within it as a result of chemical reactions, the washing effect of this water can carry away the lubricating oil, leading to severe wear. There is a synthetic polar additive (non-animal fat) that has the ability to wet metals and remove water, and can be used to reduce the impact of water. 6. Corrosion inhibitors: Compressor components can be manufactured from ordinary materials even when present in small amounts, along with CO2, H2S, chlorides, and other potentially corrosive gases. But as long as moisture is present, all compressor components in contact with gases must be made of corrosion-resistant materials or use lubricants that enhance the compressor’s resistance to corrosion. The erosion inhibitor must be used in combination with water removal and wetting additives. Even in the presence of water, this mixture of additives enables the lubricant to form a tightly adhering film on the metal surface, thereby sacrificing the lubricant itself to neutralize acidic corrosive agents and protect critical metal components. 7. Antioxidants: Oxygen reacts with the hydrocarbon molecules in lubricating oils, forming a light brown crystalline deposit of the ash type. This substance is insoluble in petroleum solvents or cleaners, and the oxidation rate doubles for every 8°C increase in temperature. For lubrication in the crankcase at an operating temperature of 60°C, ordinary inhibitors are sufficient, but they are far from adequate for cylinders operating at temperatures above 149°C. If there is 2% excess oxygen in the medium, a large amount of grayish sediment will form within weeks. To solve this problem, a high-temperature oxidant must be added. 8. Antifoam additives: When lubricant is discharged from the compressor cylinders, it becomes mixed with air and forms \"foamy sludge\"; such lubricant needs to pass through a liquid separator. If it is necessary to remove lubrication from the gas stream, 3–5 ppm of an active antifoaming agent must be added to the lubricating oil in order to quickly break up the gas bubbles. 9. Anti-emulsification additives: When the exhaust temperature is high, the lubricating oil mixed with gas combines with water, forming a soap-like black precipitate on the inner walls of the pipes and in the cooling tubes. To solve this problem, anti-emulsifying additives need to be added to the lubricating oil. 10. The ACC-ET liquid metal surface friction treatment agent from the United States uses fine metal particles in a unique patented formula. It does not alter the properties of the original lubricant; instead, it utilizes the existing lubricant as a medium to transport the oil-containing metal particles contained in ACC to the friction surfaces of the metal components. This creates a compressible lubrication layer on those friction surfaces, with the fine metal particles serving as its framework, thereby effectively separating the two friction surfaces and preventing further wear. “The micrometal particles in “ACC” continuously deposit and accumulate in the recesses of the uneven friction surface, filling in the worn areas and thus repairing the components. “The micro-metal particles in “ACC” can not only repair wear on mechanical components but also automatically adjust the friction gap, allowing the equipment to return to its original designed gap. “The design concept of the “ACC” dynamic processing metal friction parts surface effectively solves the global problem of part wear. ““ACC” is a suspension (a mixture of solid and liquid phases) produced through special processing methods; it possesses excellent lubricating properties and can repair or fill cracks and defects in metal surfaces. It consists of tens of thousands of tiny metal spheres (with a diameter of 2–8 microns) uniformly dispersed within the same carrier. Carriers are usually made by adding ordinary lubricating oils or greases along with some other ingredients. The physicochemical properties of this suspension are very stable. Each metal sphere is surrounded by liquid; when the spheres are suspended in the liquid and subjected to pressure, the pressure is transmitted to the surface of the spheres from all directions through the liquid, and the resultant force is zero. Therefore, the pellets can withstand high pressure without deforming. However, in the absence of a liquid, the metal pellets may be compressed and deformed, losing the advantage of rolling friction. 　 Parameters for selecting lubricants for different media: Abroad, countries such as the United States, Germany, Japan, and the United Kingdom have carried out bench test studies on compressor oils, aiming to use actual compressors in tests to assess the tendency of these oils to form carbon deposits and their service life. The research project on \"Bench testing and selection techniques for reciprocating air compressor oils\", led by Xi’an Jiaotong University in China and involving the Shanghai 703 Research Institute and Jinxi Refining and Chemical Plant, has gained recognition within the industry and passed the technical evaluation by Sinopec. For the assessment of carbon deposition tendency, this project uses the wp110 type single-row two-stage water-cooled differential air compressor, while the Z-0.2/10 type single-cylinder vertical air-cooled air compressor is used as the testing machine for lifespan evaluation. It is hoped that new standards will be introduced as soon as possible, as the current GB12691-90 standard for air compressor oils (mineral oil type) is insufficient to meet the guidance needs of a wide range of users.

Shuimoshi said, “There are more clearance gaps to measure for compression.” The fit clearance of the bearing shells, large-end shells, and small-end shells as well as the clamping force on the back of these shells, as well as the fit clearance between the crosshead and the pin. The tension of the crankshaft. Gap in the upper track. The vertical and horizontal runout values of the piston rod. Clearances at the dead centers before and after operation, opening clearances of the piston ring support rings, radial clearances with the cylinder liner, and axial clearances with the piston groove. Axial gap between packing seals, radial gap with the packing box, and gap at the packing ring cut. \"Radial clearance between the oil scrapper ring and the piston rod,\" but it does not specify the exact fit clearance. Many people hold magical views regarding the clearance between equipment components. Whether it’s air compressors, fans, centrifuges, pumps, or cars and trains on the roads, as well as airplanes in the sky, there are only three types of fit between their components: clearance fit, interference fit, and transition fit. According to the equipment’s precision grade, simply select the matching relationship in the Mechanical Handbook. For a clearance fit with higher precision, choose H7/g6; if a tighter fit is required, select H7/k6, H7/m6, H7/n6, H7/s6, H7/P6, etc., depending on the load magnitude. For the clearance fit of the connecting rod bearings in your air compressor, the interference fit between the piston and pin, the interference fit or transition fit between the crankshaft and bearings, or the fits used in the assembly of various components in a vehicle, please refer to the manual. Experienced blacksmiths have rich knowledge in terms of gaps; in fact, **there are standards available for reference, and as long as you read more, you will find the answers.