stop valve fault analysis and treatment

The stainless steel bellows stop valve is installed on the pipeline of marine power plant. During the use of the valve, the valve stem leaks and the valve stem is rusted. Although it has been repaired, the problems are repeated. By analyzing the cause of the failure, appropriate solutions were adopted to eliminate the fault and ensure the function of the valve.

The leakage of stainless steel bellows stop valve is generally divided into internal leakage and external leakage, and there are many reasons for leakage. Endocrine is the factor that liquid medium contains solid impurities, which destroy the sealing surface and cause failure. Combined with the analysis of field application, the causes of valve stem leakage are mainly related to valve structure, working environment and operation mode.

1. Structure

The valve rod adopts double sealing structure of bellows and packing. The bellows is welded with inner ring and outer liner ring to form bellows assembly, and then welded with valve rod and guide body to prevent medium from leaking out through the valve stem. The horizontal key I moves upward until the upper end face of the flat key I contacts the lower end face of the lower packing. Because the lower packing is made of PTFE material, if the valve is excessively opened, the flat key I will be embedded into the packing, and the valve can no longer be opened and closed, and the bellows assembly will be killed, resulting in medium leakage along the valve stem. The tensile length and compression amount of bellows are determined according to the stroke of the valve. If the limit tension or compression is exceeded, the bellows may be damaged, resulting in rupture of small braided pipe and sealing failure. Therefore, it is necessary to increase the valve opening and closing limit device, so that the bellows has been in the design range of expansion and contraction in the process of valve opening and closing.

2. Working environment

The bad working environment of bellows stop valve is also a cause of its failure. Because the bellows stop valve installed in the ship body has been working in salt fog environment for a long time, and the upper part often has condensate dripping, which causes the upper thrust ball bearing erosion, and in severe cases, it leads to the contact erosion with the valve stem.

3. Exercise

In use, if the bellows stop valve is excessively opened or closed, the valve may not be able to meet the requirements of shutdown. When the valve is excessively closed, the sealing surface may be damaged, resulting in sealing failure when the valve is used again. When the valve is opened excessively, the bellows assembly may be manipulated, resulting in valve leakage.

4. Improvement

By analyzing the problems existing in the valve, the structure, operation and environment of the valve are improved.

First of all, increase the limit welfare fee of flat key I. add a thick stainless steel packing pad to the PTFE lower packing to prevent the packing from becoming dirty and limiting the valve stem.

When the valve is closed, if the valve cannot be closed, it should not be forced to close, but open the valve, flush with fluid for a period of time, and then close again and again. If it still can not be closed, the grinding sealing surface should be checked. When the valve is opened, when the valve is opened to a certain height and the valve stem encounters small resistance, do not inherit the forced opening as far as possible, so as to prolong the service life of the valve stem and its sealing components.

When installing the globe valve with thrust ball bearing on the upper part of the valve stem, it is necessary to avoid condensed water directly dripping on the valve seat and causing the valve stem to rust.

After the improvement of the bellows stop valve, there are no failures such as bellows cracking, stem rust and leakage, and the valve is in good condition.