I. Causes of valve leakage
1. Causes of internal leakage
• Sealing surface damage: When the valve is used for a long time, the impurity particles in the medium will cause erosion and wear on the sealing surface. For example, in a slurry pipeline containing solid particles, such as the pulp conveying pipeline in the paper industry, solid fibers and additive particles will constantly rub the sealing surface of the valve. Frequent opening and closing operations will also cause wear and tear on the sealing surfaces, as there will be relative movement between the sealing surfaces each time they are opened and closed, which will lead to poor sealing over a long period of time.
• Sealing material failure: The effects of temperature and pressure are important factors leading to the failure of sealing materials. In high-temperature environments, such as valves in high-temperature oil and gas pipelines in refineries, sealing materials such as rubber can lose their elasticity due to overheating, or even carbonize. Under high pressure, the sealing material may be squeezed out of the sealing surface, thus losing the sealing effect. In addition, chemical corrosion can also damage the sealing material. For example, in chemical production, acidic or alkaline media will corrode sealing materials and reduce their performance.
• Valve selection error: If the pressure rating of the valve is not selected properly, when the actual working pressure exceeds the rated pressure of the valve, the sealing surface may be deformed, resulting in internal leakage. Problems may also arise if the valve structure is not suitable for the medium characteristics. For example, for media containing fibers, if a valve structure that easily clogs the channel is selected, it may affect the normal closing of the valve and cause internal leakage.
2. Causes of external leakage
• Leakage at the connection between the valve body and the valve cover: Loose connection bolts are one of the common reasons. During the process of thermal expansion and contraction caused by vibration or temperature changes of the pipeline, the bolts may gradually loosen. For example, in a large thermal pipeline system, due to frequent temperature changes, if the connecting bolts between the valve body and the valve cover are not tightened regularly, gaps are likely to occur, causing medium leakage. In addition, damage to the sealing gasket can also cause leakage. The gasket may lose its sealing performance due to long-term pressure, aging or corrosion by the medium.
• Packing seal leakage: Poor packing installation can cause leakage. If the packing is not loaded evenly, or the pressure of the packing gland is improperly adjusted, if it is too loose, the packing will not fit the valve stem tightly, and if it is too tight, the packing may be damaged or the valve stem may be worn, causing the medium to leak out. Moreover, the filler will wear out and dry after long-term use, and lose its sealing function. For example, the gate valve in the water supply and drainage pipeline will be prone to leakage after long-term use and aging of the filler.
II. The detection method of valve leakage
1. Visual inspection
• For external leakage, it can be judged directly by observing whether there is medium seepage, dripping, or droplets, mist, etc. formed on the valve surface. In some small water systems, for example, observing for water stains around the valves can be a preliminary indicator of external leakage. For internal leakage, if there is a transparent pipe section behind the valve, you can observe whether there is any sign of medium flowing in the pipe.
2. Pressure detection
• Static pressure detection: When the valve is closed, a certain static pressure is applied to the inlet side of the valve, and then the outlet side pressure is monitored through equipment such as pressure sensors. If the outlet pressure rises significantly within a period of time, it indicates that the valve has internal leakage. For example, in a hydraulic system, pressurize the inlet of a closed valve to a certain value, such as 10MPa, and then observe the outlet pressure. If the outlet pressure rises to more than 1MPa within a few minutes, it can be determined that there is internal leakage.
• Differential pressure detection: Install pressure sensors on both sides of the valve to measure the pressure difference on both sides when the valve is closed. Normally, the pressure difference between the two sides of a well closed valve should stabilize at a small value (depending on the system conditions). If the pressure difference keeps decreasing, it means there is an internal leak. This method is more commonly used in some high-precision industrial piping systems, such as fluid transfer piping in the pharmaceutical industry.
• Ultrasonic detection: An ultrasonic signal is generated when a medium leaks from a leak. These signals can be detected using ultrasonic detectors. By comparing the strength of the leak signal and the background noise, the severity of the leak can be determined. This method is very effective for detecting small leaks and can be performed without affecting system operation. For example, in natural gas transmission pipelines, small gas leaks can be detected using ultrasonic detectors.
• Bubble detection: For valves with liquid media, you can immerse the valve in water or apply a foaming agent such as soapy water to the part of the valve that may leak. If there is a leak, bubbles will be generated. This method is simple and easy, but it is not very convenient for some large valves or valves that are not easy to soak. For example, for valves in some small chemical experimental devices, this method can be used to quickly detect whether there is a leak.
III. Solutions and preventive measures for valve leakage
For valve leakage problems, the following solutions and preventive measures can be taken:
1. Solution
• For sealing surface problems, repair work such as grinding and polishing can be performed to restore its sealing performance.
• For packing problems, replace with suitable packing and install correctly as specified.
• For valve body and bonnet problems, replace the valve with a reliable quality valve or repair it.
• For sealing ring problems, new sealing rings should be replaced and rolled and welded as required.
• For leakage caused by improper operation, operator training should be strengthened to ensure correct operation of the valve.
2. Preventive measures
• Select high-quality valve products to ensure that their sealing performance and pressure resistance meet system requirements.
• Strengthen the quality control of valves and conduct strict quality inspection and testing on valves.
• Perform regular maintenance on valves and replace damaged seals and fasteners in a timely manner.
• Standardize operating behaviors and operate strictly in accordance with the valve operating instructions.
• Perform regular inspections on valves to detect and address potential problems promptly.
