1. Use the stainless steel bellows stop valve to install on the pipeline of the ship's power plant. During the use of the valve, leakage at the valve stem and rust of the valve stem occurred, although it has been repaired. But the problem recurred. After analyzing the cause of the failure, a suitable solution was adopted to eliminate the failure and ensure the performance of the valve.

2. Problem analysis

Bellow Seal Globe Valve leakage is generally divided into internal leakage and external leakage. There are many reasons for leakage. Endocrine is generally due to the failure of the sealing surface caused by the liquid medium containing solid impurities. Combined with the analysis of the on-site usage, the reason for the leakage of the valve stem is mainly related to the valve structure, working environment and operation mode.

2.1 Structure

The valve stem adopts a double sealing structure of bellows and packing. The bellows are welded with the inner lining ring and the outer lining ring to form a bellows assembly and then welded with the valve stem and the guide body to block the leakage of the medium through the valve stem. The valve stem moves up and down from the flat key I upwards until the upper-end surface of the flat key I contacts the lower end surface of the lower packing. Because the lower packing is made of PTFE material, if the valve is opened too much, the flat key I will be embedded in the packing, the valve can no longer be opened and closed, and the bellows assembly will be killed, causing the medium to leak along the valve stem. The stretched length and compressed amount of the bellows are determined according to the stroke of the valve. If the stretch or compression exceeds the limit, the bellows may be damaged, causing the small pipe to rupture and seal failure. Therefore, it is necessary to increase the limit device for opening and closing the valve, so that the bellows always expand and contract within the design range during the opening and closing process of the valve.

2.2 Working environment

The harsh working environment of the carbon steel stainless steel globe valve is also a cause of its failure.

Because the Carbon Steel Stainless Steel Globe Valve installed in the ship body has been working in a salt spray environment for a long time, and there is often condensation dripping on the upper part, causing corrosion of the upper thrust ball bearing, and in severe cases, contact with the valve stem corrosion

2.3 Operation

If the bellows stop valve is opened or closed excessively during use, the valve may not meet the relevant performance requirements. When the valve is closed excessively, the sealing surface may be crushed, causing the seal to fail when the valve is used again. When the valve is opened excessively, the bellows assembly may be operated, causing the valve to leak.

Bellow Seal Globe Valve

3. Improve

After analyzing the problems of the valve, the structure, operation, and environment were improved. The first is to increase the limit welfare fee of the flat key I and add a 3mm thick stainless steel packing pad to the lower packing of PTFE material to prevent the packing from getting dirty and restrict the valve stem.

When the valve is closed, if the valve cannot be shut off, it should not be forced to close. Instead, the valve should be opened, washed with fluid for a period of time and then closed again. If it still cannot be closed, check the ground sealing surface. When the valve is opened, when the valve is opened to a certain height, after the valve stem encounters a small resistance, try not to continue to force it to extend the life of the valve stem and its sealing components. For the stop valve with thrust ball bearing on the upper part of the valve stem, during installation, try to avoid the direct drip of condensed water on the valve and cause the valve stem to rust.

4. Conclusion

After the improvement of the bellows stops the valve, there is no recurrence of bellows cracking, valve stem rusting and leakage, etc., and it is in good condition.