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I. Condition Monitoring and Fault Detection 1. Valve Cover Temperature Monitoring Regularly check and record the surface temperature of the gas valve’s outer cover, and make graphical records of these values. By combining this data with the operating parameters measured by instrumentation (such as temperature and pressure), it is possible to analyze the performance of the gas valve, estimate its remaining lifespan, and schedule maintenance activities appropriately. 2. Detection of the operating sound of air valves By using tools such as stethoscopes to listen to the sounds produced by the movement of the valve elements, and by comparing these sounds with those of valves of the same type and name, it is easy to identify valves that are not functioning properly; this allows for timely maintenance to be scheduled. 3. Analysis of changes in process parameters Once a gas valve leaks, it will cause changes in temperature, pressure, or flow rate. By changing these parameters, it is possible to determine which stage of the gas valve, or even which specific gas valve, is malfunctioning. II. Analysis of the cause of the failure 1. Dirty medium or external impurities entering Solid impurity particles, driven by the high-pressure airflow in the compressor, strike the air valves violently, causing damage to the components; or dirt gets trapped between the sealing surfaces, resulting in the air valves failing to function properly. 2. Liquid in the medium: The presence of liquid in the medium or a malfunction in the compressor’s gas-liquid separator can cause liquid hammer to occur in the gas valves. As a result of these additional shocks, the gas valves fail more rapidly, and this is manifested as abnormal noises during compressor operation. 3. Excessive lubricant in the cylinders The compressor cylinders are lubricated with oil; if too much oil is used, the excess lubricant can cause sticking inside the gas valves, leading to the valves breaking due to delayed closing or opening. 4. Changes in operating conditions Each valve in a compressor is designed for specific operating conditions; significant fluctuations in these conditions or deviations from the design values for extended periods of time will cause the valves to fail quickly. 5. Restarting after a long period of inactivity When the compressor is left unused for some time, lubricant in the cylinders or liquid present in the medium accumulates within these cylinders. This not only leads to corrosion of the cylinders and valves, but also, during startup when the engine is cold, failure to remove this accumulated liquid from the cylinders or to clean the valves results in the engine starting with liquid present, which can easily cause liquid slugging and oil viscosity issues. 6. Other reasons Unit resonance, improper operation, environmental factors, etc., can also affect the service life of air valves. III. Maintenance 1. Inspection and repair of components (1) Check for damage to the valve components. Check whether the valve disc and spring are broken, twisted, or deformed, and whether the spring has lost its elasticity; if any of the above conditions exist, replace them. (2) Check for wear and scratches on the valve disc and valve seat sealing surfaces. When the sealing surface has slight wear, pitting, unevenness, or scratches, it can be ground on a grinding bench. During grinding, a “00”-shaped motion should be used to ensure even grinding of the sealing surface, preventing one-sided tilting and radial marks, thus ensuring a tight fit between the sealing surfaces. When the sealing surface is severely damaged, the valve disc or seat must be replaced. (3) Check the wear at the interface between the valve disc and the lift limiter guide rail. When the valve disc is fitted on the guide rail, move the valve disc radially by hand; the displacement shall not exceed 0.5 mm, otherwise it should be discarded. 2. Assembly When assembling the various components of the air valve after inspection and repair, the following points should be noted: (1) The components must be clean ； (2) The contact condition between the valve disc and the valve seat, the radial clearance between the valve disc and the lift limiter, the lift amount of the valve disc, and the specifications of the spring all meet the design requirements ； (3) When replacing internal parts (such as valve plates, buffer plates, springs, etc.), they must all be replaced at the same time. 3. Leak testing Leak testing is required before installing the air valve. Currently, a large number of new types of non-metallic materials are used in the manufacture of valve discs, and the technique of performing hydrostatic pressure tests on gas valves using kerosene or water is no longer entirely suitable. Since non-metallic materials are prone to deformation due to external factors such as temperature and humidity, and springs alone are not sufficient to correct this, kerosene leak testing may result in all air valves being deemed unqualified. Pneumatic valves achieve sealing through the pressure difference between the inside and outside; only testing methods similar to those used in the operating environment can properly evaluate such valves. Currently, a new type of air valve leakage testing method, namely the airtightness testing method, simulates these operating conditions and can accurately detect leaks in air valves. IV. Installation 1. Selection of new air valves Each air valve is designed specifically for particular operating conditions; deviations from these conditions or improper design of the air valves can increase the frequency of abnormal shutdowns of the equipment. A qualified air valve should feature high efficiency and energy savings, good airtightness, timely operation, long service life, low noise, and minimal temperature rise. During a complete replacement, valves from different manufacturers cannot be used together on the same compressor (especially on the cylinders of the same stage). 2. Installation (1) First, it is necessary to ensure that the system’s pipelines, cylinders, and valve seats have been thoroughly cleaned. (2) All valve gaskets must be replaced, and the valve cover bolts must be tightened evenly to prevent the valve from being misaligned. (3) When installing the compressor intake valve, it is necessary to adjust the load regulator so that there is a gap of 1–2 mm between the top of the valve stem and the valve, to ensure proper operation of the valve.