The Working Principle of Piston Compressors
A compressor is a machine that generates gas pressure energy, and it has become an indispensable key equipment in various sectors of the national economy. Currently, in applications requiring high pressure, piston compressors are commonly used.
There are many types of piston compressors, and their structures are complex, but their basic structures are generally similar. In fact, a natural gas compressor may have hundreds of parts, but these parts can be basically divided into four sections according to their functions: the cylinder section, the transmission section, the body section, and auxiliary equipment. During the operation of the compressor, the electric motor drives the crankshaft to rotate, and the piston performs reciprocating motion through the connecting rod. As the crankshaft rotates one revolution, the piston completes one reciprocating motion, and the process of suction, compression, and exhaust in the cylinder is successively realized, thus completing one working cycle.
Compression Process:
(1) Suction Process: When the piston moves to the left, the working volume in the cylinder gradually increases, and the pressure gradually decreases. When the pressure drops slightly below the pressure in the intake pipe, the gas in the intake pipe pushes open the intake valve and enters the cylinder until the piston reaches the farthest left position (also known as inner dead center), where the working volume is at its maximum, and the intake valve begins to close.
(2) Compression Process: When the piston moves to the right, the working volume in the cylinder decreases, and the gas pressure gradually increases. Since the intake valve has a check valve function, the gas in the cylinder cannot flow back into the intake pipe. At the same time, because the pressure of the gas in the exhaust pipe is higher than that inside the cylinder, the gas in the cylinder cannot flow out through the exhaust valve, and the gas in the exhaust pipe cannot enter the cylinder due to the check valve action of the exhaust valve. At this time, the amount of gas in the cylinder remains constant, and as the piston moves to the right, the gas pressure continues to rise.
(3) Exhaust Process: When the piston moves to a certain position to the right, the pressure of the gas in the cylinder rises slightly above the pressure of the gas in the exhaust pipe, and the gas pushes open the exhaust valve into the exhaust pipe until the piston reaches the farthest right position (also known as outer dead center). The exhaust valve closes, and the piston moves left again, repeating the above process.
Main Advantages of Piston Compressors:
(1)Wide Pressure Range: Piston compressors can be used for low pressure (including vacuum), medium pressure, high pressure, and ultra-high pressure applications.
(2) High Efficiency: They have higher efficiency compared to rotary compressors and centrifugal compressors. The adiabatic efficiency of large piston compressors is typically over 80%.
(3) Strong Adaptability: Piston compressors have a wide range of discharge capacities and can maintain high efficiency even at lower discharge capacities. Additionally, the discharge capacity is minimally affected by fluctuations in discharge pressure. Furthermore, the impact of gas density on compressor performance is not significant, making piston compressors versatile machines.
Disadvantages of Piston Compressors:
Complex Structure and High Vulnerability: Piston compressors have a complex structure with numerous vulnerable components, leading to difficulties in maintenance, inspection, and installation.
(2) Limitation on Rotational Speed: Due to the inertia force of reciprocating motion, piston compressors operate at lower rotational speeds. When a large discharge capacity is required, the compressor body becomes large and heavy, requiring a large foundation. Therefore, piston compressors are not suitable for applications requiring high discharge capacities.
(3) Discontinuous Exhaust: Piston compressors produce discontinuous exhaust, resulting in airflow pulsation. Severe pulsation can lead to airflow pulsation resonance, causing damage to pipelines or components.
(4) Lubrication Requirement: Lubricating oil is typically used inside the cylinder to ensure smooth operation. This results in oil carryover in the compressed gas. If high gas purity is required, the task of purifying the compressed gas becomes challenging.
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