Common causes of external and internal leakage in valves (1)

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This post was last edited by Jinma Water Damage Control on 2026-1-20 at 10:45. I. External leakage from valves: Visible leaks. External leakage from valves refers to the leakage of fluid from parts such as the valve stem, flanges, and packing boxes into the surrounding environment; it is a type of leakage that is easily visible, and it is also a key focus during on-site inspections. External leakage is often associated with factors such as aging of sealing components, improper installation, and harsh operating conditions. It can be categorized into the following three types: 1. Leakage at the valve stem area – The valve stem area is a common site for external leakage, especially under conditions of frequent opening and closing. The primary cause of such leaks is the failure of the packing seal. A stuffing box is typically used for sealing between the valve stem and the valve cover; the packing presses against the surface of the valve stem under the tension exerted by the bolts, thereby creating a sealing barrier. However, during long-term operation, the packing wears out due to the back-and-forth or rotational movement of the valve stem. Coupled with factors such as medium corrosion and temperature changes, the packing gradually ages, hardens, and cracks, resulting in gaps in the seal; as a consequence, the medium seeps out along the valve stem. Furthermore, improper packing installation can also lead to leaks; issues such as misaligned packing ring joints, uneven compression force, and insufficient number of packing layers can all reduce the sealing efficiency. For valves equipped with bellows seals, welding defects, fatigue cracking, or corrosion-induced perforations in the bellows can also lead to leakage at the valve stem area; such leaks are more common under conditions of high temperature, high pressure, and severe corrosion. 2. Leakage at the flange connection. The flange connection is the primary method of linking valves to pipelines, and its sealing reliability depends on the quality of the flange sealing surfaces, the performance of the gaskets, and the bolt tightening technique. Common causes of leakage at the flange include aging, deformation, or damage of the gasket, which prevents it from fully filling the microscopic gaps in the flange sealing surfaces. The flange sealing surface has defects such as scratches, dents, and rust, which result in poor fit between the sealing surfaces ； The bolt tightening torque is uneven, resulting in an unbalanced load on the gaskets and the appearance of gaps in certain areas ； Excessive fluctuations in operating pressure or temperature exceed the tolerance range of the gasket, resulting in its failure. In transportation systems for flammable, explosive, toxic, and hazardous materials, leaks from flanges pose particularly serious risks; once a leak occurs, it can easily lead to fires, explosions, or poisoning incidents. 3. Leakage caused by casting defects in the valve body. Such leaks are usually due to quality issues in valve manufacturing; for example, defects such as sand holes, pores, and cracks may exist during the casting of the valve body. These defects go unnoticed during factory testing, but once the valve is put into operation, the pressure of the fluid causes these defects to expand over time, ultimately leading to leakage of the fluid. Furthermore, long-term erosion and corrosion can also reduce the wall thickness of the valve body; when the wall thickness falls below the safe limit, perforation and leakage occur. Such leaks are characterized by their high degree of concealment; in the initial stage they may be merely minor seepages, but they can deteriorate rapidly over time, leading to serious consequences.