How to determine whether a valve is leaking internally or externally?

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To determine whether a valve is leaking internally or externally, it is necessary to distinguish between them based on different symptoms, testing methods, and locations. The following are the specific steps and methods for determination: 1. Detection of internal leakage Internal leakage refers to the situation where, after the valve is closed, the medium (liquid or gas) still leaks through the valve seat or sealing surface into the downstream pipes or equipment. Judgment method: If, after the valve is closed, the pressure shown on the downstream pressure gauge continues to rise, or the flow meter still shows a reading, there may be an internal leak. Compare the changes in downstream parameters (such as temperature and pressure) before and after the valve is closed. For temperature monitoring, if the temperature in the pipeline downstream of the valve rises abnormally (for example, in the case of steam valves), it may be due to an internal leak that causes continuous flow of the medium. Ultrasonic testing uses an ultrasonic leak detector to inspect the pipeline downstream of the valve body: the presence of high-frequency sound waves indicates that the medium is leaking through the valve seat. Check the position of the valve stem to confirm that the valve is fully closed (by checking the position of the handwheel and the status of the actuator), in order to rule out internal leakage caused by incomplete closure. Test of discharge ports: Some valves, such as safety valves and check valves, are equipped with discharge ports; if these ports continue to discharge the medium, there may be an internal leak. II. Determination of external leakage External leakage refers to the leakage of the medium from outside the valve body (such as the valve stem, flanges, connections at the valve body, or the packing box) into the surrounding environment. Judgment method: Visually inspect the outside of the valve to check for any leakage of fluid, frosting (in the case of low-temperature fluids), or signs of rust. Check for liquid, bubbles, or crystals around the valve stem, at the flange bolt connections, and in the welds of the valve body. The soapy water test involves applying soapy water to the suspected leak site; if bubbles form, it indicates an external leak (applicable to gas valves). Gas detectors can be either combustible gas detectors or toxic gas detectors, used to locate the source of leaks (suitable for hazardous gases). Infrared thermography uses an infrared thermal camera to detect the temperature distribution on the surface of the valve body; areas with low or high temperatures may indicate potential leak points. External leakage at the valve stem in the stuffing box is commonly caused by a failure in the stuffing box seal; if there is leakage of fluid around the valve stem, it is necessary to check whether the packing is aged or loose. III. Key differences between internal leakage and external leakage
Internal leakage: Leakage occurs at the valve seat sealing surface (inside the valve).
External leakage: Leakage takes place on the outside of the valve body (such as the valve stem, flanges, welds, etc.).
Destination of the fluid: It flows into downstream pipes or equipment; it leaks into the environment.
Detection tools: Ultrasonic leak detectors, pressure gauges, soapy water, gas detectors, visual inspection.
Risks: Reduced system efficiency, energy waste, environmental pollution, safety hazards (fires, poisoning).
IV. Common causes
Causes of internal leakage: Damaged valve seats, worn sealing surfaces, the valve not being closed properly, impurities in the fluid that cause the valve core to get stuck. Causes of external leakage: aging of the valve stem packing, failure of the flange gasket, cracks in the valve body, and loose bolts. Precautions: When handling high-pressure or toxic substances, protective equipment must be worn to avoid direct contact with the leaking substances. If it is not possible to determine the type of leak, it is recommended to contact a professional or use specialized equipment (such as an endoscope to inspect the valve seat). External leaks must be addressed immediately to prevent safety accidents ； For internal leakage, it is necessary to assess its impact on the system before deciding whether to shut down the system for repairs. Through the above methods, it is possible to quickly identify the type of leak and take targeted measures.