Analysis of Fault Causes and Treatment Methods for Bellows Globe Valves

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　　Leakages in bellows globe valves generally fall into two categories: internal leakage and external leakage, with various causes leading to such leaks. Endocrine failure is generally caused by solid impurities in the liquid medium damaging the sealing surface. Based on an analysis of on-site usage, the reasons for external leakage of the valve stem are mainly related to the valve structure, operating environment, and methods of use. 　　 　　 1 Structure: The valve stem features a dual-sealing structure using a bellows and packing. The bellows is welded to the inner and outer lining rings to form a bellows assembly, which is then welded to the valve stem and the guide element, thereby preventing the medium from leaking out through the valve stem. The valve stem moves up and down; key I moves upward until the upper surface of key I comes into contact with the lower surface of the lower packing. Since the packing is made of PTFE material, if the valve is opened too far, the flat key I will get embedded in the packing, preventing the valve from being opened or closed anymore; this will also damage the bellows assembly, resulting in leakage of the medium along the valve stem. The extension and compression amount of the bellows are determined based on the valve’s stroke; if the extreme limits of extension or compression are exceeded, the bellows may be damaged, leading to its rupture and loss of sealing performance. Therefore, it is necessary to add limit devices for opening and closing the valve, so that during the valve’s opening and closing process, the bellows remains within the designed range of expansion and contraction. 　　 　　 2 Working environment: The harsh working conditions of bellows globe valves are also a cause of their failures. Since the bellows globe valve installed inside the ship operates for long periods in a salt spray environment, and with condensation droplets often falling on its upper part, this leads to corrosion of the upper thrust ball bearings; in severe cases, it causes contact corrosion with the valve stem. 　　 　　 Operation 3: During use, if the bellows globe valve is opened or closed excessively, it may prevent the valve from meeting the relevant performance requirements. If the valve is closed too tightly, it is possible to damage the sealing surface, resulting in failed sealing when the valve is used again. If the valve is opened too much, it may affect the bellows assembly, resulting in leakage from the valve. 　　 　　 Improvements to the analysis of failure causes in bellows globe valves: After analyzing the problems existing in these valves, improvements were made to their structure, operation, and operating environment. Firstly, increase the limit stop allowance for flat key I; add a stainless steel gasket with a thickness of 3 mm as an additional filler made of PTFE material, in order to prevent the filler from getting dirty and to provide limit stopping for the valve stem. 　　 　　 　　When the valve is closed and it fails to stop the flow, one should not apply more force to try to close it; instead, the valve should be opened, allowed to be flushed with fluid for a while, and then closed again. This process should be repeated. If the valve still cannot be closed, the polished sealing surfaces should be inspected. When the valve is being opened, once it has been opened to a certain extent and the valve stem encounters slight resistance, try not to force it open any further in order to extend the lifespan of the valve stem and its sealing components. 　　 　　 　　For globe valves with thrust ball bearings on the upper part of the valve stem, during installation, care should be taken to prevent condensed water from dripping directly onto the areas around the valve opening, as this could cause rusting of the valve stem.