Analysis of problems encountered in application of stainless steel bellows

Generally speaking, stainless steel bellows in the application may encounter internal leakage or leakage phenomenon, resulting in a lot of reasons, usually due to liquid medium containing solid impurities damage the sealing surface caused by. The causes of valve stem leakage are mainly related to valve structure, working environment and service mode.

The structural stem uses stainless steel bellows and packing double seal structure, bellows lining ring and outer lining ring welded into bellows components, and then with the stem and guide body welding, so as to block the medium through the valve stem leakage. The distance between the upper and lower of the valve rod moves upwards until the upper end of the flat key is contacted with the lower end of the lower packing. Because the lower packing is made of PTFE material, once the valve is over opened, the flat key I is inserted into the packing so that the valve can no longer be opened and closed, and the components of the bellows are also killed, leading to the leakage of the dielectric along the valve stem. The length and compression amount of the stainless steel bellows are determined according to the distance of the valve. Once it exceeds the limit tension or compression, it may destroy the bellows, resulting in the failure of the small tube and the sealing failure. Therefore, it is necessary to increase the valve opening and closing of the limit device, so that the valve opening and closing process, bellows has been in the design range of expansion.

Here’s an example. The stop valve of stainless steel bellow is installed on the pipeline of the power plant of the ship. During the use of the valve, there are some problems, such as the leakage of the valve stem and the rust of the valve stem. But the problems will happen again and again. By analyzing the causes of the failure, using appropriate solutions to remove the fault, thereby protecting the performance of the valve.

Through the analysis of the valve problems, the structure, operation and environment were improved. The first is to increase the limited welfare cost of flat key I, and ask the lower filler of PTFE material to ask for a thick 3mm stainless steel filler pad, so as to avoid the contamination of the filler and the valve stem limit.

When the valve is closed, if the valve can not be stopped, do not force forcibly shut down, but to open the valve, flush with fluid for a period of time after closing again, again and again, if not yet closed, check the grinding sealing surface. When the valve is opened, when the valve opens to a certain height, the valve stem meets small resistance, try not to continue to force open, thereby extending the life of the valve stem and its sealing components. Valve with thrust ball bearing on the upper part of the valve, in the installation, we should try to avoid condensation water directly drop in the valve account, resulting in corrosion of the stem position.

In addition, the bellows stop valve working environment is bad, but also cause one of the reasons for its easy failure. Because the body is installed on the corrugated pipe valve for long-term work in the salt spray environment, and is also often condensate dripping water, lead to corrosion of the upper thrust ball bearings, it will lead to more serious stem contact corrosion, operation in use if excessive open or closed bellows globe valve, may the valve can not meet the relevant performance requirements. Over close the valve, it may crush the sealing surface, resulting in seal failure when the valve again. When the valve is opened excessively, the stainless steel bellows assembly may be operated to make the valve leak out.

Source: China Stainless Steel Bellows Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)

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