How to judge whether the manual valve is well sealed

As a key control element in industrial pipeline systems, the sealing performance of manual valves directly affects the safety, operating efficiency and environmental protection of the system. Poor sealing will not only lead to medium leakage, energy loss and environmental pollution, but may also cause safety accidents such as equipment corrosion, fire and explosion. Scientifically and accurately judging whether the manual valve is well sealed is an important link to ensure the smooth progress of industrial processes. The determination of sealing performance includes not only the selection of valve body structure and sealing materials, but also the specific technical methods of on-site inspection and daily maintenance.

First of all, a well-sealed manual valve should have zero leakage or extremely small leakage characteristics. Zero leakage is an ideal state, usually used in high pressure, high temperature, hazardous media or high cleanliness requirements. Small leakage allows slight medium leakage within a certain standard range. The evaluation of valve sealing performance should be compared and judged according to the leakage level specified in national standards, industry specifications or manufacturer's technical documents.

When evaluating the sealing status of manual valves, it can be carried out from four levels: appearance inspection, operation experience, functional testing and instrument testing. The appearance inspection mainly observes whether there is medium leakage, rust marks or crystal accumulation at the valve sealing surface, packing and valve body connection. If obvious liquid traces or scaling are found on the surface, it is very likely that the seal has failed. There should be no oil or water marks on the packing gland, and the bolts should be tightened appropriately without looseness or cracks.

The operating feeling reflects the contact state of the valve sealing surface and whether the mechanical transmission is smooth. If there is abnormal stagnation, excessive resistance or repeated adjustment during operation, it may be due to damage to the sealing surface, foreign matter embedded or leakage of the valve stem packing. The valve stem should rotate evenly and smoothly, and the handwheel or operating lever should not be loose or make abnormal sounds. When the seal is poor, the opening and closing feeling becomes lighter or cannot be in place after the valve is opened or closed.

Functional testing is the core link in judging the sealing performance. The most commonly used detection methods are air tightness test and liquid tightness test. The air tightness test usually uses air, nitrogen or inert gas as the medium, and uses the pressure holding method to detect whether there is gas leakage on the valve sealing surface. During the test, the design pressure is applied to the valve, and the sealing surface should maintain a stable pressure without a significant drop. The liquid tightness test is mostly used in water systems to check whether there is water drop leakage after the valve is closed. For key valves, special detection equipment is used for trace leakage detection, and helium leak detector or fluorescent leak test technology is used to improve sensitivity.

Instrument detection includes modern technologies such as ultrasonic leak detection, pressure decay test, infrared imaging, etc. Ultrasonic leak detection achieves non-destructive detection by detecting high-frequency sound waves generated by gas leakage at the valve seal. Pressure decay test determines the size of the leak by monitoring the rate of pressure change in the system. Infrared imaging can detect abnormal temperature distribution caused by valve leakage and assist in locating sealing defects. Combining multiple detection methods can improve the accuracy and comprehensiveness of sealing performance evaluation.

The material properties of valve seals play a decisive role in the sealing effect. Metal hard-sealed valves achieve tight closure through metal sealing surfaces and are suitable for high temperature and high pressure occasions. Soft-sealed valves use elastic materials such as rubber, polytetrafluoroethylene, and fluororubber to achieve good sealing. The sealing material needs to be selected according to the properties of the medium, temperature and pressure. In long-term operation, aging, hardening, and corrosion of seals will cause seal failure, and they should be replaced and maintained regularly.

The maintenance of sealing performance also depends on the rationality of valve design. The matching accuracy between the valve disc and the valve seat, the clamping force of the valve stem packing, the hardness of the sealing surface material and the surface roughness all affect the sealing quality. Wear, corrosion or mechanical damage of the sealing surface are the main causes of leakage. The valve manufacturing process must ensure the flatness and surface treatment of the sealing surface to improve the wear and corrosion resistance. During the installation process, the medium impurities should be prevented from entering the sealing surface.

In daily operation management, the operator should strictly follow the operating procedures to open and close the valve to avoid long-term pressure on the valve when it is not fully opened or closed. Prevent the material from deforming and failing due to the long-term compression of the soft seal by the valve disc. For long-term static valves, they should be opened and moved regularly to check the sealing status. During maintenance, focus on checking the tightness of the packing gland and the integrity of the sealing surface, and remove impurities and lubricate in time.

In emergency situations, if the valve is found to be poorly sealed, measures should be taken quickly to prevent the leakage of the medium from expanding. The fluid can be cut off through the bypass valve or the spare valve first, and a detailed maintenance plan can be arranged. During repair, determine whether to replace the sealing ring, packing or the entire valve core assembly according to the leakage location. The technicians should select the most suitable repair plan based on the valve's usage history and medium conditions.