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The air valve is an important component of an air compressor. It is precisely through the control of air valves that the processes of intake, compression, exhaust, and expansion can proceed alternately in a continuous manner in an air compressor. The performance of the air valve directly affects the compressor’s exhaust volume, exhaust temperature, power consumption, and operational reliability. The air valve is one of the main vulnerable components in piston-type air compressors; let’s explore the causes of its damage and the preventive measures. Reciprocating air compressors belong to the category of positive-displacement compressors; they are compressors that sequentially draw in and discharge a certain volume of gas from a closed space in order to increase the static pressure, with one or several pistons moving back and forth used to change the volume inside the compression chamber. At present, reciprocating compressors mainly include piston air compressors, compressors used in chemical processes, as well as compressors for the oil and gas industry. Piston air compressors are currently developing in the direction of medium-pressure and high-pressure applications, a level that screw compressors and centrifugal compressors cannot yet reach. The air valve is an important component of an air compressor. It is precisely through the control of air valves that the processes of intake, compression, exhaust, and expansion can proceed alternately in a continuous manner in an air compressor. The performance of the air valve directly affects the compressor’s exhaust volume, exhaust temperature, power consumption, and operational reliability. The air valve is one of the main vulnerable components in piston-type air compressors; let’s explore the causes of its damage and the preventive measures. I. Structure of the air valve: Reciprocating air compressors generally use automatic valves, whose opening and closing are achieved through the pressure difference acting on the air valve and the elastic force of the spring. (1) Valve seat: The valve seat is used to support the valve disc, and it has airflow channels that are controlled by the valve disc for opening and closing. The valve seat must withstand the impact from the valve disc; therefore, it is usually made of impact-resistant materials such as steel, cast iron, alloy cast iron, rare earth ductile iron, or bronze. (2) Valve disc: The valve disc is an important component for controlling the opening and closing of the air flow passage. In operation, in addition to being periodically impacted against the valve seat and lift restrictor due to air flow thrust, spring force, and inertial force, it is also subjected to air pressure pressing against the valve seat during valve closure, which makes it prone to wear and deformation. To ensure airtightness, its mating surface with the valve seat must be smooth, flat, and free of defects. The valve disc is generally made of alloy steel with high strength, good toughness, wear resistance, and corrosion resistance; it undergoes quenching and tempering treatments during processing, and its thickness is usually between 0.8 mm and 3 mm. To improve impact resistance, both sides of the valve disc are ground. The valve disc can also be made of non-metallic materials such as plastic and nylon. This type of valve disc offers good sealing performance, impact resistance, and a long service life, but it has poor strength and suffers from significant thermal deformation. (3) Spring: The main function of the spring is to ensure that the air valve closes promptly, as well as to reduce the impact between the valve disc and the lift limiter. Due to the elasticity of the valve disc itself, segmental valves usually do not require an additional spring. When the valve is in operation, the spring is periodically compressed and extended; therefore, it is usually made of high-grade spring steel wire with high fatigue strength. Whether a spring can perform its intended function depends crucially on whether its elasticity is appropriately selected. The valve spring is too stiff, resulting in delayed valve opening, high resistance losses, and significant impact of the valve disc on the valve seat ； It’s too soft; the valve does not close in time, causing air to flow back and reducing the exhaust volume. More seriously, due to the delayed seating of the valve plate, the piston has already started its return stroke. At this point, the force exerted by the airflow acts in the same direction as the force of the spring, causing the valve plate to seat with greater acceleration and thus resulting in a greater impact. It should be noted that overly soft springs have a particularly severe impact on the operation of the exhaust valve. Therefore, the springs of regular exhaust valves are stiffer than those of intake valves. (4) Lift limiter: The lift limiter is used to restrict the lift of the valve disc, and also serves as a guide for the movement of the valve disc. The lift of the valve disc has a significant impact on the operation of the gas valve. Excessive lift results in greater impact when the valve closes, as well as delayed closure ； If the lift is too small, although the impact force on the valve disc is reduced, the flow area of the valve decreases, which in turn increases the resistance loss as air flows through the valve. II. Force analysis during the operation of the air valve. Damage to the air valve is primarily caused by mechanical damage, wear, and corrosion of its components. The valve disc and spring are the most prone to damage components. There are two main types of loads that the valve disc experiences during operation: ① The uniform load caused by the pressure difference on both sides of the valve disc. Since the pressure inside the cylinder changes periodically from intake pressure to exhaust pressure, it constitutes a variable load with a pulsating cycle. Under such loading, the valve disc will suffer from bending fatigue failure, with circumferential cracks forming near its average diameter ； ②The impact load caused by collision with the lift limiter and valve seat. The magnitude of its impact force is related to the mass of the valve disc and the speed at which it moves. III. Signs of valve failures (1) Signs of a leaky intake valve ① The temperature of this valve rises significantly, and the valve cover becomes hot ； ②If the suction valve on the high-pressure stage leaks, the pressure in the intercooler increases ； ③The suction and exhaust temperatures of this cylinder have increased ； ④The airflow of the air compressor has decreased. (2) Signs of exhaust valve leakage: ① Abnormal heating of the valve and its cover ； ②The exhaust temperature of this class increases ； ③Intercooler air pressure increases (leakage in the downstream exhaust valve) or decreases (leakage in the upstream exhaust valve) ； ④The airflow of the air compressor has decreased. IV. Causes of valve damage: In each working cycle, the valve plate impacts once against the lift limiter and the valve seat. Practical applications have shown that the modes of failure of valve plates are as follows: (1) Radial fractures caused by impact loads; this type of failure is a fatigue failure resulting from multiple impacts with low energy ； (2) Stress concentration caused by internal defects in the valve disc material becomes the source of fatigue failure under cyclic loading ； (3) Friction and wear occur between the valve disc and other components during operation, leading to the failure of the valve disc ； (4) During operation, the valve is surrounded by the medium, which causes high-speed erosion and corrosion. As a result, the protective film on the valve surface is damaged, leading to localized corrosive pitting or cavities on the valve plate. V. Precautions and preventive measures: Reducing impact force is an important measure to extend the lifespan of the valve disc. To increase the service life of gas valves, during design and manufacturing, materials with low mass are used for the valve discs on one hand ； On the other hand, structurally minimize the lift height and increase the spring force. In addition, the following precautions and measures should be taken when using air valves: (1) All parts, especially the valve discs and springs, must be purchased in accordance with standards. (2) When assembling the air valve, check all parts against the drawings. In particular, the lift washer directly affects the lift height of the valve disc; if the lift height is too large, the impact kinetic energy acting on the valve disc increases ； If the lift height is too low, power consumption increases. For example, if the speed of a piston air compressor is 1480 r/min, the corresponding stroke length should be adjusted to 1.5–1.0 mm; measurement is carried out using the lead compression method to ensure that the air valves operate in optimal condition. (3) Maintain accurate records of the air valve’s operation, and establish maintenance schedules based on the characteristics of the air valves to replace them on a regular basis. At the same time, the operating condition of the gas valve should be checked regularly; generally, simple methods such as observing and analyzing changes in pressure ratios and temperatures at various stages, as well as feeling and listening, are used to determine whether the gas valve is functioning properly. (4) Properly maintain the air valves in accordance with the specified maintenance intervals; the main tasks of maintenance include cleaning, inspection, and airtightness testing. During cleaning, cracks on the air valve are often concealed by oil residue and not easily visible; they become clearly apparent only after cleaning them with a brush. In reality, due to inadequate inspection, gas valves with minor defects such as cracks or uneven surfaces are often installed and put into use, which allows these defects to gradually worsen and lead to valve failures. Additionally, the damaged surfaces of the valve seat and lift restrictor should be repaired promptly, and wear-prone components such as valve plates and springs should be replaced in a timely manner. It should be noted here that if one of the valve spring mechanisms is damaged, all the other springs in that valve need to be replaced as well, in order to ensure that a uniform spring force is applied to the valve disc. Records should be kept for the maintenance of air valves. Taking into account the service life of the vulnerable components, the valve discs and springs must be replaced entirely after 400 hours of continuous use, while the service life of the valve seat is 8000 hours; replacement should also be considered at that point. (5) The installation of the air valve assembly must strictly comply with the assembly technical requirements. During installation, care must be taken to avoid omissions or incorrect installations. For example, when installing the air valve on the engine body, if the middle tightening screw is forgotten to be tightened, the entire air valve becomes loose on the engine body; this can cause knocking during operation and result in damage to the air valve. When repairing the valve seat and lift restrictor using methods such as turning and grinding, it is important to follow the repair specifications in order not to reduce the strength of the valve body. (6) Usually, minor abnormalities in air valves will show signs of change over a considerable period of time before they become completely damaged; operators can use visual inspection, listening, and tactile testing to determine which air valve is having problems. But in many cases, since the entire unit still appears to be functioning, no further inspection is carried out, allowing the air compressor to operate with faults present, which exacerbates the damage to the air valves. Therefore, operators should regularly check the operating condition of the air valves; even minor faults should be taken seriously and resolved promptly without being ignored. (7) Soften the cooling water, and pay attention to performing regular or continuous drainage from the intercooler, aftercooler, and gas-liquid separator, in order to reduce scaling in the heat exchangers and maintain their heat exchange efficiency. (8) Regularly check the sealing condition of areas such as the cylinder water jacket or cylinder surface, as well as the integrity of the intercooler. Address any issues found promptly to prevent cooling water from entering the cylinders and causing severe shocks that could damage the valve plates.