Ball valve is a new type of valve which came out in 1950s. In a short period of more than 30 years, it is one of the valve varieties that have developed rapidly in recent ten years. It is mainly used to cut off, distribute and change the flow direction of medium in pipeline. The ball valve with V-shaped opening also has good flow regulation function. The ball valve can be closed tightly with 90 degree rotation and small rotation torque. The completely equal inner cavity of the valve body provides a small resistance and straight passage for the medium. The ball valve not only has simple structure and good sealing performance, but also has small volume, light weight, less material consumption, small installation size, small driving torque, simple operation, easy to realize quick opening and closing, easy operation and maintenance within a certain nominal diameter range. It is suitable for general working media such as water, solvent, acid and natural gas, and also suitable for media with poor working conditions, Such as oxygen, hydrogen peroxide, methane and ethylene. The valve body of ball valve can be integral or combined.

Bellows globe valve is a kind of globe valve, which is one of the more widely used valves. Its popularity is due to the small friction between sealing surfaces in the process of opening and closing, relatively durable, small opening height, easy manufacturing and convenient maintenance. It is not only suitable for medium and low pressure, but also suitable for high pressure. The closing principle of the stop valve is to make the sealing surface of the valve disc and the sealing surface of the valve seat close together by relying on the pressure of the valve rod to prevent the medium from flowing. It can be used to control the flow of air, water, steam, various corrosive media, mud, oil, liquid metal and radioactive media. Therefore, this type of shut-off valve is very suitable for cut-off or regulation and throttling. Because the opening or closing stroke of the valve stem is relatively short, and it has a very reliable cut-off function, and because the change of the valve seat opening is directly proportional to the stroke of the valve disc, it is very suitable for regulating the flow. The bellows seal globe valve adopts the bellows seal design, which completely eliminates the shortcomings of the common valve stem packing seal, such as fast aging and easy leakage. It not only improves the use of energy efficiency, increases the safety of production equipment, reduces the maintenance cost and frequent maintenance, but also provides a clean and safe working environment. Advantages of bellows globe valve Double seal design (bellows + packing) if the bellows failure, the stem packing will also be avoided. External leakage, and meet the international sealing standards. No fluid loss, reduce energy loss, improve plant equipment safety. Long service life, reduce the number of maintenance, reduce operating costs. Durable bellows seal design ensures zero leakage of valve stem and provides maintenance free condition.

Stop valve is one of the more widely used valves. The reason why it is widely popular is that in the process of opening and closing, the friction between the sealing surfaces is small, it is relatively durable, the opening height is not large, it is easy to manufacture, and it is convenient to maintain. It is not only suitable for medium and low pressure, but also suitable for high pressure. The closing principle of the stop valve is to make the sealing surface of the valve disc and the sealing surface of the valve seat close together by relying on the pressure of the valve rod to prevent the medium from flowing. It can be used to control the flow of air, water, steam, various corrosive media, mud, oil, liquid metal and radioactive media. Therefore, this type of shut-off valve is very suitable for cut-off or regulation and throttling. Because the opening or closing stroke of the valve stem is relatively short, and it has a very reliable cut-off function, and because the change of the valve seat opening is directly proportional to the stroke of the valve disc, it is very suitable for regulating the flow. The stem axis of the stop valve is perpendicular to the sealing surface of the valve seat. The relatively short opening or closing stroke of the valve stem and its reliable cut-off action make the valve very suitable for medium cut-off or adjustment and throttling. Once the valve disc of the stop valve is in the open state, the contact between the valve seat and the sealing surface of the valve disc will be no longer, and it has a very reliable cut-off action, so this kind of valve is very suitable for medium cutting or regulating and throttling. Once the stop valve is in the open state, there will be no contact between the valve seat and the sealing surface of the valve disc, so the mechanical wear of the sealing surface is small. Because most of the valve seats and the valve disc are easy to repair or replace, it is not necessary to remove the whole valve from the pipeline when the sealing elements are replaced, which is very suitable for the occasions where the valve and the pipeline are welded together. When the medium passes through this kind of valve, the flow direction changes, so the flow resistance of the stop valve is higher than that of other valves. The commonly used stop valves are as follows: 1. Angle stop valve; In the angle globe valve, the fluid only needs to change its direction once, so that the pressure drop through the valve is smaller than that of the conventional globe valve. 2. DC stop valve; In direct flow or Y-shaped stop valve, the flow channel of the valve body is inclined to the main flow channel, so the damage degree of the flow state is smaller than that of the conventional stop valve, so the pressure loss through the valve is correspondingly smaller. 3. Plunger type stop valve: this type of stop valve is a variant of conventional stop valve. In this valve, the disc and seat are usually designed based on the principle of plunger. The valve disc is polished into a plunger and connected with the valve stem. The sealing is realized by two elastic sealing rings on the plunger. The two elastic sealing rings are separated by a collar, and the sealing ring around the plunger is firmly pressed by the load exerted on the valve cover by the valve cover nut. The elastic sealing ring can be replaced and can be made of various materials. The valve is mainly used for "opening" or "closing", but it is equipped with special plunger or special ring, which can also be used to adjust the flow.

The leakage of bellows globe valve is generally divided into internal leakage and external leakage, and there are many reasons for leakage. In general, the liquid medium contains solid impurities to destroy the sealing surface and cause failure. Combined with the analysis of the field application, the main reasons for the leakage of the valve stem are related to the valve structure, working environment and operation mode. 1 Structure: The valve stem adopts the double sealing structure of bellows and packing. The bellows is welded with the inner ring and outer ring to form the bellows assembly, and then welded with the valve stem and guide body to prevent the medium from leaking out through the valve stem. The valve stem moves up and down from the flat key I until the upper end face of the flat key I contacts the lower end face of the lower packing. As the lower packing is made of PTFE material, if the valve is opened excessively, 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, resulting in medium leakage along the valve stem. The stretching length and compression of the bellows are determined according to the valve stroke. If the stretching or compression exceeds the limit, the bellows may be damaged, resulting in small braided pipe rupture and seal failure. Therefore, it is necessary to increase the opening and closing limit device of the valve, so that the bellows can expand and contract within the design range during the opening and closing process of the valve. 2. Working environment: The bad working environment of bellows globe valve is also one of the reasons for its failure. Because the bellows globe valve installed in the ship has been working in the salt spray environment for a long time, and there is often condensate dripping on the upper part, which causes the corrosion of the upper thrust ball bearing. In serious cases, it leads to the contact corrosion with the valve stem. 3 operation: If the bellows globe valve is opened or closed excessively in use, the valve may not meet the relevant performance requirements. If the valve is excessively closed, the sealing surface may be damaged, resulting in seal failure when the valve is used again. If the valve is opened excessively, the bellows assembly may be operated, causing leakage of the valve. The cause analysis and improvement of bellows stop valve fault are as follows After analyzing the existing problems of the valve, its structure, operation and environment were improved. The first is to increase the limit welfare of flat key I, and add a 3mm thick stainless steel packing pad to the lower packing of PTFE material, so as to prevent the packing from getting dirty and limiting the valve stem. When the valve is closed, if the valve can not be closed, it should not be forced to close, but open the valve, flush it with fluid for a period of time, and then close it 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, try not to continue to force the valve to open, so as to extend the service life of the valve stem and its sealing components. When installing the stop valve with thrust ball bearing on the upper part of the valve stem, it is necessary to avoid the condensation water dripping directly on the valve stem and causing the stem corrosion.