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

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II. Internal leakage of valves: the invisible “hidden loss” Internal leakage of valves refers to the situation where the fluid does not pass through the control channel of the valve, but instead leaks from between the sealing surfaces of the closing element (such as the valve disc, gate, ball, etc.) and the valve seat; it is a type of hidden leakage that occurs inside the valve. Since internal leaks cannot be observed directly, they often need to be detected through methods such as pressure monitoring and flow measurement. Although their hazards are not as apparent as those of external leaks, they can lead to significant energy waste and system operational failures over time. 1. Wear and damage of the sealing surface: The sealing surface is the key component that enables a valve to perform its shut-off function, and its precision and smoothness directly affect the sealing performance. In actual operation, the sealing surface can be damaged by various factors: first, the medium contains solid particles and impurities, which, during the opening and closing of the valve, can scour and scratch the sealing surface, creating grooves in it ； Secondly, when the valve is opened or closed, the closing element comes into direct contact with the valve seat; especially under high-pressure conditions, the impact forces can cause plastic deformation of the sealing surface ； Third is the corrosive effect of the medium; for example, strong acids and strong bases can corrode the material of the sealing surface, destroying its density and leading to seal failure. For forcibly sealed valves such as gate valves and globe valves, once the sealing surfaces are worn, fluid can still flow through the gaps in those surfaces even when the valve is in a fully closed position, resulting in internal leakage. 2. Inadequate opening and closing of the valve – this is a common human factor that causes internal leakage in valves. When operating the valves, the personnel did not follow the procedures: for example, gate valves and globe valves were not closed completely, and ball valves and butterfly valves were not rotated to a position where they were fully sealed, resulting in a gap between the closing element and the valve seat. Furthermore, failures in the valve actuator can also lead to improper opening and closing. Issues such as a malfunctioning limit switch in electric actuators, insufficient air pressure in pneumatic actuators, or leaks in the hydraulic system of hydraulic actuators can all result in the valve not being able to close completely, thereby causing internal leakage. 3. Deformation or jamming of the valve stem: After long-term operation, the valve stem may become bent or deformed due to factors such as medium erosion, thermal stress, and external impacts, which prevents the closing element from fitting precisely against the valve seat ； If the connection between the valve stem and the valve disc becomes loose or comes apart, it will also affect the sealing performance. Furthermore, impurities in the medium entering the gap between the valve stem and the valve cover can cause the valve stem to stick, preventing the valve from opening and closing properly and thus leading to internal leakage.