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This post was last edited by LQ198619 on 2017-5-25 11:30. VI. Structure of Reciprocating Compressors: A reciprocating compressor consists mainly of components such as the casing, crankshaft, connecting rods, piston assembly, valves, shaft seals, oil pump, energy regulation device, and oil circulation system. The following diagram shows a schematic illustration of the compressor structure. 1. Cylinder block: It consists of two parts, the cylinder block and the crankcase, and is usually cast as a single unit from high-strength gray cast iron (HT20-40). It is the structure that supports the weight of the cylinder liner, the crankshaft connecting rod mechanism, and all other components, while ensuring that these components maintain the correct relative positions with one another. The cylinder features a cylinder liner structure, which is mounted in the liner seat holes on the cylinder block, facilitating maintenance or replacement when the cylinder liner wears out. 2. Crankshaft: The crankshaft is one of the main components of a reciprocating compressor, transmitting all the power of the compressor. Its main function is to convert the rotational motion of the motor into the reciprocating linear motion of the piston through connecting rods. As it moves, the crankshaft is subjected to alternating combined loads of tension, compression, shear, bending, and torsion; under such harsh working conditions, it requires sufficient strength and stiffness, as well as wear resistance in both the main journal and the crankpin. Therefore, crankshafts are generally forged from high-quality carbon steel grades 40, 45, or 50. 3. Connecting rod: The connecting rod is the component that connects the crankshaft to the piston; it converts the rotational motion of the crankshaft into the back-and-forth motion of the piston, and transfers power to the piston so that it can do work on the gas. The connecting rod includes a rod body, a rod small-end bushing, a rod large-end bearing shell, and rod bolts. During operation, the connecting rod body is subjected to alternating tensile and compressive loads; therefore, it is generally forged from high-quality medium-carbon steel or cast from ductile iron (such as QT40-10). The rod body usually has an I-shaped cross-section, with a long hole drilled in the middle to serve as an oil passage. 4. Piston assembly: The piston assembly refers to the piston, piston pin, and piston rings together. Driven by the connecting rod, the piston assembly moves back and forth in a straight line within the cylinder; together with the cylinder, this forms a variable working volume that enables processes such as intake, compression, and exhaust. Pistons—Pistons can be divided into two main categories: cylindrical and disc-shaped. The material of the piston is usually aluminum alloy, or cast iron. The piston pin – a component used to connect the piston to the small end of the connecting rod – is subjected to complex alternating loads during operation. Piston rings—Piston rings include gas rings and oil rings. The main function of the steam ring is to create a seal between the piston and the cylinder wall, preventing the compressed gas from leaking through the gap between them ； The function of the oil ring is to distribute oil and scrape off excess lubricating oil from the cylinder walls. 5. Air valve and shaft seal: The air valve is an important component of the compressor and is considered a wear part. Its quality and performance directly affect the gas delivery volume of the compressor, power loss, and operational reliability. The valve assembly includes a suction valve and an exhaust valve; each time the piston moves up and down once, both the suction valve and the exhaust valve open and close respectively, thereby controlling the compressor and enabling it to carry out the four working processes of suction, compression, and exhaust. 6. Shaft seal – The function of the shaft seal is to prevent compressed gas from leaking outward along the extension end of the crankshaft, or to prevent outside air from entering when the pressure inside the crankcase is lower than atmospheric pressure. 7. The role of lubrication in the lubrication system: Lubrication is one of the important aspects in compressors; it not only affects the performance parameters of the compressor but also has a direct impact on its lifespan, reliability, and safety. The functions of lubrication are as follows: A. It separates the friction surfaces (i.e., the contact surfaces between moving parts such as the shaft and bearings, or piston rings and cylinder walls) with an oil film, resulting in liquid friction or semi-dry friction. This reduces the frictional work and heat generated by the compressor, as well as wear on the components, thereby improving the mechanical efficiency of the compressor and enhancing its reliability and durability. B. Carry away frictional heat to prevent the friction surfaces from becoming too hot. C. The lubricating oil fills the gap between the piston and the cylinder, as well as the friction surfaces of the shaft seals, thereby enhancing the sealing effect. D. Carry away wear debris and improve the performance of the friction surface. E. The compressor’s lubrication system also supplies oil to the energy regulation device. F. Lubrication method and lubrication system: The lubrication methods for compressors can be divided into two types: splash lubrication and pressure lubrication. Splash lubrication makes use of the mechanical action of moving parts to deliver lubricating oil to the friction surfaces that need it, and many semi-hermetic compressors employ splash lubrication. On one hand, an oil flinger is installed at the lower end of the connecting rod’s large end, which flings the oil from the crankcase onto the cylinder walls in order to lubricate the friction surfaces between the piston and the cylinder walls ； On the other hand, an oil flinger is mounted on the shaft at one end of the motor; it flings the oil and collects it in the oil collection chamber on the end cover on the motor side, which then uses the oil channels in the crankshaft to lubricate the main bearings and the rod bearings. In some small vertical open-type compressors, splash lubrication is achieved solely by the movement of the crank-slider mechanism.