In the complex system of industrial production, valves as the human body’s joints, controlling the direction and flow of various types of fluids, and its normal operation plays a key role in ensuring production efficiency and safety. However, the valve will often appear a variety of leakage problems, as if the body joints have problems, affecting the smooth operation of the entire industrial process. Next, we will analyze in detail the common valve leakage and its corresponding treatment.
Valve and bonnet leakage
Common causes
Cast iron quality defects: cast iron valve body and bonnet in the casting, if the process is not perfect, it is easy to produce trachoma, the organization is not tight enough, and even slag and other conditions. These defects are like hidden inside the valve body and bonnet “time bomb”, may cause leakage problems at any time. For example, in some small foundries, due to the limitations of equipment and technology, the production of cast iron valves in the quality inspection, it is frequently found such defects.
Cold weather risk of freezing: When the cold weather comes, especially when the temperature drops to 0 ° C and below, if there is water left inside the valve, the volume of the water will expand after freezing, like a balloon that keeps getting bigger and bigger in a small space, and ultimately cracks the valve body or valve cover. In northern winters, valves in outdoor industrial facilities are vulnerable to this situation.
Welding quality hazards: those assembled by welding the valve body and bonnet, if the welding process is not standardized, it will leave slag, not completely welded through or produce stress cracks and other problems. These welding defects can jeopardize the overall structural integrity of the valve body and bonnet, leading to leakage. Some welders are unskilled or neglect welding quality in order to meet deadlines, which can easily cause such problems.
Damage caused by external impact: cast iron valves are relatively fragile, once subjected to heavy impact, it is easy to damage, and then leakage. In the construction site, due to careless operation of workers, or material handling process collision, may lead to cast iron valve damage.
Treatment
Strictly control the casting quality: before installing the valve, the valve body and valve cover must be tested for strength in strict accordance with the relevant regulations. Only through the test to ensure that there is no casting defects in the valve, can be put into use. For example, some large industrial enterprises, will establish a special quality testing department, using advanced testing equipment, each batch of valves for detailed testing.
Do a good job of low-temperature protection measures: for valves in a low-temperature environment (0 ° C and below), to do a good job of thermal insulation or accompanying heat. You can give the valve wrapped with thermal insulation materials, or install heat tracing devices to prevent the water inside the valve from freezing. At the same time, valves that are out of service must be emptied of internal water to avoid the risk of freezing and cracking. In some cold regions of the factory, will be in the winter before the arrival of, arranged for special personnel on the valve insulation treatment and water evacuation work.
Standardize the welding process and testing: the valve body and valve cover welding should strictly follow the relevant welding procedures. After the welding is completed, not only to carry out flaw detection to see whether there are internal defects, but also to carry out strength tests to ensure that the strength of the welded parts meet the requirements. For example, some professional welding workshops will conduct regular training for welding workers to improve their welding skills, and at the same time equipped with advanced flaw detection equipment to strictly control the welding quality.
Avoid external damage to the valve: in the daily production and operation process, it is strictly prohibited to pile up heavy objects on the valve, and should never use a hand hammer to strike cast iron and non-metallic valves. For large-diameter valves, the installation should be equipped with a special bracket to support the weight of the valve to prevent damage due to its own weight or external forces. At the construction site, obvious warning signs will be set up to remind workers to pay attention to protecting the valves.
Valve leakage of the specific means of repair
Adhesive plugging method: If the leak is caused by the pressure medium and the leakage is small in the sandhole area, you can first polish the vicinity of the leakage point until it reveals a metallic luster. Then use a tapered pin to align with the leak point and drive it in with appropriate force. Immediately thereafter, a fast curing adhesive is utilized to quickly coat the vicinity of the pin to form a new solid sealing structure, thus stopping the leak. This method utilizes the special properties of the adhesive and is effective in some small leakage problems.
Top pressure mechanism to plug the leakage method: the top pressure mechanism is fixed on the side of the regulating valve, adjust the top pressure screw, so that its axial just aligned with the leakage point. Then rotate the top pressure screw, through the screw end of the rivet tightly pressed against the leakage site, forcing the leakage to stop. This method is suitable for some small pressure leakage, the operation is relatively simple.
Nut welding plugging method: when the valve leakage medium pressure is low, leakage, you can find a leakage point than the inner diameter of more than double the nut, so that the leakage medium from the nut outflow. Then the nut welded to the valve body, and then with a bolt with the same specifications of the nut, in the bottom of the nut placed on the rubber gasket or asbestos gasket, the top of the bolt wrapped in raw tape screwed into the nut, as a way to stop the leak. This method is less expensive and is often used in some small factories.
Diversion welding method (for high-pressure leakage): Prepare a piece of iron plate with a round hole in the center, and weld an isolation valve with the appropriate caliber of the round hole to the round hole of the iron plate. Open the isolation valve, the central hole of the iron plate against the leakage point on the valve body, so that the leakage medium through the central hole of the iron plate and isolation valve outflow. If the fit surface is not tight, you can place a rubber or asbestos pad on the fit surface, and then weld the iron plate periphery with the valve body, and finally close the isolation valve to realize the re-seal. This method is suitable for high pressure and large leakage, and requires certain welding skills and operating experience.
Welding repair method (for high-temperature and high-pressure, leakage is not large and the valve shape and size allows): first of all, the valve body and the leakage point related to the gap (excluding the leak itself) all welded. Take a section of length according to the site environment (generally about 200mm), the diameter is greater than the leakage point of the pipe, will be an appropriate control valve welded to one end of the pipe and fully open the valve. Weld the other end of the pipe to the leakage point, close the regulating valve, you can stop the leakage. This method requires a high degree of welding craftsmanship and requires specialized welders to operate.
Understand these common valve leakage problems and treatment methods, can help industrial practitioners in the production process to find and solve the problem in a timely manner, to ensure the normal operation of the valve, to ensure the smooth running of production, to avoid production stagnation and safety hazards brought about by the valve leakage.
Translated with DeepL.com (free version)
