What are the differences between piston compressors and screw compressors?

Centrifugal compressors belong to the velocity-type category, while piston and screw compressors are of the volume-type category. Centrifugal compressors rely on high-speed blades to transfer energy to the refrigerant gas flowing continuously within the pipeline, thereby giving it a very high speed and increasing its pressure at the same time. They offer advantages such as high cooling capacity, low weight and small size per unit of power, minimal space requirement, no vulnerable components such as valves, pistons, or piston rings, the ability to achieve oil-free compression, stable and reliable operation, light equipment foundations, low pulsation in the air supply, and low maintenance costs. However, their disadvantages include lower efficiency, the need for larger individual units, limited adaptability to varying operating conditions, and higher noise levels compared to piston compressors. Piston compressors are among the earliest types of compressor designs, and they remain one of the most versatile and highly efficient compressors available. A piston compressor moves the piston forward within the cylinder through a connecting rod and crankshaft. If compression is performed using only one side of the piston, it is called single-acting. If both the upper and lower sides of the piston are used, it is called double-acting. Piston compressors have a very wide range of applications, with almost no limitations. It can compress air as well as gases, with almost no need for any modifications. Piston compressors are the only type designed to compress air and gases to high pressures for uses such as breathing air. The configurations of piston compressors can range from single-cylinder designs suitable for low-pressure/low-capacity applications, to multi-stage designs capable of compressing to very high pressures. In multi-stage compressors, air is compressed in stages, with the pressure increasing at each stage. Compression capacity: The power range of the CompAir piston compressor series is from 0.75 kW to 420 kW (1hp to 563hp), with working pressures ranging from 1.5 bar to 414 bar (21 to 6004psi). Its typical applications include: gas compression (CNG, nitrogen, inert gases, landfill gases); high-pressure air (air for breathing in scuba tanks, seismic surveys, pneumatic circuits, etc.); PET bottle blowing; engine starting; and industrial use. The screw compressor is a type of positive-displacement rotary compressor. Since there is no re-expansion of gas remaining in the clearance volume, there is a very small gap between the rotor and the casing, with no sliding friction between them, which results in high internal and mechanical efficiency. As it lacks intake and exhaust valves, it has few vulnerable components, making maintenance straightforward; moreover, its service life is long. It is currently widely used and is set to see further adoption. Its drawbacks are higher noise levels and the fact that the capacity of a single unit cannot be too small. The piston compressor is a traditional type of positive-displacement compressor and is the most widely used at present. This type of compressor features mature manufacturing techniques, a wide range of operating pressures, strong adaptability to varying conditions, slightly lower heat generation compared to screw compressors, generally lower rated speeds, pulsations in gas flow, and certain vibrations during operation. Its structure is complex, it has many vulnerable components, and its maintenance cycle is short. Its noise level is lower than that of centrifugal and screw compressors, which makes it the dominant choice for small and medium-sized refrigeration systems. The screw compressor belongs to the category of positive-displacement compressors, with its “pistons” taking the form of screws ； This is the most commonly used type of compressor today. The main components of a screw compression element are the male rotor and the female rotor; these two rotors move towards each other, causing the volume between them as well as within the chamber to gradually decrease. The pressure ratio of a screw type depends on the length and shape of the screw, as well as the shape of the exhaust port. The screw element is not equipped with any valves, so there are no mechanical forces that could cause imbalance. Therefore, it can operate at high shaft speeds, while also offering high flow rates and compact external dimensions. Compression capacity: The power range of the CompAir rotary screw compressor series is from 4 kW to 250 kW (5 to 535 hp), with a working pressure of 5 bar to 13 bar (72 to 188 psi). Its typical applications are: food, beverages, brewing, aerospace, the automotive industry, electronics, manufacturing, the petrochemical industry, healthcare, hospitals, and pharmaceuticals. For general use, centrifugal compressors and screw compressors are suitable for large-scale refrigeration and air conditioning systems, while piston compressors are commonly used in small and medium-sized refrigeration and air conditioning systems. This post was last edited by lioe on 2009-2-6 at 09:09

The working principles and applicable scenarios of the two are different; in simple terms, a piston compressor is like a pump. Piston compressors are large in size and difficult to maintain; they are suitable for high-pressure applications, with pressures of several dozen or even hundreds of kilograms. Screw compressors are smaller in size and easier to maintain; they are suitable for low-pressure applications, with pressures usually below 15 kilograms. Additionally, this post suggests that the boss move to the conveyor equipment discussion area.

From the perspective of use and maintenance, piston-type and screw-type systems differ in that screw-type systems operate smoothly, produce less noise, require less space, and have almost no maintenance needs. Piston-type systems, on the other hand, generate more noise and have higher maintenance costs, but they are cheaper. In principle, they all belong to the category of positive displacement pumps, but their operating mechanisms differ: one operates by reciprocation while the other operates by rotation. I’m not sure if this answer will work!

I. Piston Compressors (1) Working Principle of Piston Compressors When the crankshaft of a piston compressor rotates, the piston moves back and forth via the linkage mechanism; as a result, the working volume formed by the inner wall of the cylinder, the cylinder head, and the top surface of the piston changes periodically. When the piston of a piston-type compressor begins to move from the cylinder head, the working volume inside the cylinder gradually increases. At this point, gas enters the cylinder through the intake pipe, pushing open the intake valve, until the working volume reaches its maximum value at which point the intake valve closes ； When the piston of a piston-type compressor moves in the opposite direction, the working volume inside the cylinder decreases, causing the gas pressure to rise. When the pressure inside the cylinder reaches and slightly exceeds the exhaust pressure, the exhaust valve opens and the gas is expelled from the cylinder, until the piston reaches its extreme position at which point the exhaust valve closes. When the piston of the piston compressor moves in the opposite direction again, the aforementioned process repeats. In summary, as the crankshaft of a piston compressor rotates one full cycle, the piston moves back and forth once, allowing processes such as intake, compression, and exhaust to occur sequentially within the cylinder, thus completing one working cycle. (II) Advantages of piston compressors: 1. Piston compressors have a wide range of applicable pressures; they can achieve the desired pressure regardless of the flow rate ； 2. Piston compressors have high thermal efficiency and require less electricity per unit of work ； 3. It has strong adaptability, meaning it has a wide exhaust range and is not affected by pressure levels; it can cope with a broad range of pressure conditions as well as various cooling capacity requirements ； 4. High maintainability of piston compressors ； 5. Piston compressors have low requirements for materials; they are usually made of ordinary steel, which makes them easy to process and results in lower costs ； 6. Piston compressors are technically mature, with extensive experience accumulated in their production and use ； 7. The installation system of piston compressors is relatively simple. (III) Disadvantages of piston compressors: 1. Low rotational speed, and the machines are large and heavy ； 2. Complex structure, many vulnerable components, and high maintenance requirements ； 3. Irregular exhaust flow, resulting in pulsations in the air stream ； 4. There is significant vibration during operation. For more information on piston air compressors, please visit www.fsair.cn. Piston compressors are the most widely used and produced type of compressor in various applications, especially in small to medium-sized refrigeration systems. 2. Screw compressors: Screw compressors consist of two intermeshing screw rotors enclosed within a casing; the gap between the rotors as well as between the casing and the rotors is only 5–10 microns. The main rotor (also known as the male rotor or convex rotor) is driven by an engine or electric motor (with electric motors being the most common). The other rotor (also known as the female rotor or concave rotor) is driven either by an oil film created by oil injection from the main rotor, or by synchronous gears at the ends of both the main rotor and the female rotor. So there is no metal contact in the drive (theoretically). The length and diameter of the rotor determine the compressor’s displacement (flow rate) and discharge pressure; the longer the rotor, the higher the pressure ； The larger the rotor diameter, the greater the flow rate. The spiral rotor groove is filled with gas as it passes through the air intake. As the rotor rotates, its grooves are enclosed by the casing walls, forming compression chambers. Once these grooves are sealed, lubricating oil is injected into the compression chambers to provide sealing. Cooling and lubrication functions. As the rotor rotates to compress the lubricant + gas (referred to as the oil-gas mixture), the volume of the compression chamber decreases, compressing the oil-gas mixture toward the exhaust port. As the compression chamber passes through the exhaust port, the oil-gas mixture is discharged from the compressor, completing one cycle of suction—compression—exhaust. Each rotor of the screw machine is supported by anti-friction bearings, which are fixed by end caps located near the end of the shaft. The intake side is supported by roller bearings, while the exhaust side is supported by opposing tapered roller bearings. Typically, it is the bearings on the exhaust side that position the rotor; these are thrust bearings that resist axial forces, bear radial loads, and provide the necessary minimum clearance for axial movement.

Principle of screw air compressors 1. Intake process: The intake port on the intake side of a screw air compressor must be designed in such a way that the compression chamber can draw in air adequately. Screw air compressors do not have separate intake and exhaust valve assemblies; instead, intake is regulated by the opening and closing of a control valve. As the rotors rotate, the grooves between the main and auxiliary rotors reach their maximum volume when they align with the intake port openings. At this point, the air in these grooves is in contact with the air outside at the intake port. Since all the air in the grooves is expelled during exhaust, the grooves are in a vacuum state at the end of the exhaust process. When they align with the intake port again, external air is drawn in and flows axially into the grooves of the main and auxiliary rotors. When the air fills the entire tooth groove, the inlet-side end face of the rotor moves away from the inlet of the casing, and the air between the tooth grooves is thus trapped. 2. Sealing and conveying process: At the end of air intake, the tooth tips of the main and auxiliary rotors come into contact with the casing, thereby sealing off the air within the tooth grooves and preventing it from flowing out. The two rotors continue to rotate, with their tooth peaks and tooth grooves aligning at the intake side, and this alignment point gradually moves toward the exhaust side. 3. Compression and fuel injection process: During transportation, the meshing surfaces gradually move toward the exhaust end; in other words, the gap between the meshing surfaces and the exhaust port gradually decreases. The gas within this gap is progressively compressed, resulting in an increase in pressure. This is what happens. Meanwhile, due to the pressure difference, lubricating oil is also sprayed into the compression chamber to mix with the air inside. 4. Exhaust process: When the meshing surfaces of the rotors come into alignment with the exhaust port of the casing (at this point the pressure of the compressed gas is at its highest), the compressed gas begins to be expelled. This continues until the meshing surfaces between the teeth move to the exhaust end face; at that point, the space between the meshing surfaces of the rotors and the tooth grooves at the exhaust port becomes zero, thus completing the exhaust process. At the same time, the length of the tooth grooves between the meshing surfaces of the rotors and the intake port reaches its maximum, and the intake process resumes

Very Clear!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!1

The difference between the two is clear; what was said upstairs already explains it well! Applicable scenarios: Compared to screw compressors, centrifugal compressors have lower pressure but higher and more stable flow rates, while screw compressors have higher pressure but lower flow rates. Therefore, centrifugal compressors are suitable for applications where a stable flow rate is required and the pressure isn’t very high. Screw compressors are appropriate for situations with high pressure requirements. Additionally, in some cases the compressed medium cannot contain any oil or gas, which means that centrifugal compressors must be used! Finally, there are maintenance and price considerations. Screw compressors have many vulnerable components such as pressure valves and piston rings, which are prone to damage and difficult to repair. Centrifuges are easy to maintain, but they are more expensive