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Design and Analysis of Single Sealing Valve Soft Sealing Structure
1 Introduction Control valves (also known as control valves) are the ultimate control elements of the process control loop, but they are also a weaker link in the system's process control loop. Regulating valve by regulation type can be divided into regulation type, regulation cut off and cut off type 3, including regulating cut off and cut off type regulating valve, the leakage must reach ASME B16. 104VI level (ie bubble level) requirements. Regulating cut-off valve is usually used in soft-sealed structure to achieve Level VI leakage requirements. In this paper, the most used amount of direct stroke control valve, the majority of manufacturers are in the production of single-seat control valve soft seal design of the technical details of the analysis. 2 Structure Analysis 2.1 The traditional design of single-seat control valve soft seal structure Since the 1980s, with the implementation and implementation of China's reform and opening up policy, some control valve manufacturers introduced the well-known foreign manufacturers of valve technology and products so that our country Control valve product variety and quality has been significantly improved. Typical of these are the Yamatake Corporation's Cv3000 Series Regulators, such as the typical HTS single-seat, trim-type regulator (ie, soft seal) in the Cv3000 Series (Figure 1). The soft sealing ring of the regulating valve is inlaid into the valve handle by the valve head and the screw, and the valve seat is screwed on the valve body by the screw connection. 1 Body 2 Seat 3 Tip 4 Soft Seal 5 Screw 6 Valve Handle Figure 1 Conventional Single Seat Control Valve Soft Seal Construction When the valve is closed, the raised surface of the valve seat fits into the soft seal ring ( The soft sealing ring is usually made of an elastic material such as polytetrafluoroethylene), where the deformation of the elastic material encloses the convex surface of the valve seat, thereby ensuring a reliable sealing effect without too much thrust of the valve stem. It can be seen from this that the valve can only be sealed with a suitable force when it is closed, and that the resilient material itself can sustain this closing force permanently. This is particularly relevant for the opening of valves that are permanently closed. As the surface of the elastic material is not permanently deformed, so to ensure that the valve seat and valve flap repeatedly repeated opening and closing of the seal. In addition, because the valve disc embedded in the elastic material can correct the minor deviation of the seal pair in the concentricity, the manufacture position accuracy requirements of the valve disc and the valve seat can be lower. However, this form of soft seal structure also has some drawbacks. The first is difficult to limit the size of the closing force, even when the flap soft seal ring contact with the valve seat, the closing action can not stop in time, so that the elastic material prone to permanent deformation, especially when the valve is closed for a long time, the valve flap Soft ring has long been subject to overload pressure caused permanent deformation, open and then closed easily failure. Secondly, during the valve opening process, due to the throttling effect of the valve flap, the high-speed flow of the medium occurs in a short period of time when the valve is opened. At this time, the soft seal ring is subjected to great pressure drop, which will affect the soft seal Erosion of the ring surface, resulting in the rapid destruction of its surface. Therefore, the soft seal structure is usually limited to the case where the pressure drop is less than 3 MPa. In addition, the structure has great drawbacks in assembly, disassembly and maintenance. First of all, the soft seal ring is inserted into the valve handle by screwing the valve head and the screw. In order to ensure that the screw is not loosened, usually the screw is coated with an appropriate curing glue or fixed by means of riveting and spot welding Screws, which give great inconvenience when you remove the soft seal ring again. Followed by the seat with threaded connections, the need for special tooling to be assembled and disassembled, extremely inconvenient for on-site maintenance. 2.2 improved design of soft seal structure With the development of industrial technology, users want higher quality valves, but also require the use of the valve to improve the level of maintenance. This puts forward new requirements for engineering and technical personnel, in addition to careful design of high quality and high level of the valve, the rational selection and the correct operation, but also to facilitate maintenance and repair personnel demolition, convenient and quick, so that all kinds of accidents And maintenance time to a minimum. Thus, for single-seat control valve, there has been shown in Figure 2 improved soft-seal design. In this kind of structural design, the metal retaining ring and the soft sealing ring are used instead of the traditional structure of the fixed soft sealing ring with a screw. The design of the direct pressure structure of the pressing sleeve and the seat sealing gasket replaces the traditional structural valve Seat with threaded connection design. The advantage of this design is that when the valve flap and the valve seat reach the final closed position, part of the valve flap to the valve seat is borne by the metal stop ring and is directly transmitted to the valve seat, so that the soft seal ring is ruled out due to overloading, And metal retaining ring also provides some secondary sealing effect. Direct-pressure structural design has also changed the need for special tooling can be removed threaded seat design, assembly and disassembly, on-site maintenance and replacement are very convenient. Improved soft seal structure design also has some shortcomings. First of all, once the soft seal ring fails, the metal stop ring can only play a temporary seal, must be replaced as soon as possible. In addition, if the medium with solid particles, it is very easy to get stuck in the valve flap and seat, hindered the seat seal will cause leakage, and then due to high-speed erosion of the media so that the valve seat surface erosion damage. 2.3 new soft seal structure design In order to make up for the lack of the above structure, there has been shown in Figure 3, a new single-seat control valve soft seal structure design. The new structure, the sealing pair with a metal seal and PTFE elastic seal double seal design. Metal seal seat can play a supporting role to prevent the soft seal ring is crushed due to excessive pressure. The soft seal ring is supported by the elastic o-ring and protected by the metal pressure ring. The additional metal pressure ring eliminates the risk of overloading the soft sealing element. This results in a bubble level of up to 500,000 cycles (Class VI) Sealed, leakproof. Figure 4 for the valve fully closed state, metal seal and elastic seal at the same time, sealing tight and reliable. Figure 5 is the valve fully open state, flexible elastic ring to restore flexibility. The valve has just opened the moment, the seal at the outer edge of the media due to the more acute turbulence, will cause the seal vibration, so that the sealing material fatigue failure. The new structure due to the metal seat ring flange protection, soft seal ring will not be washed by the fluid, not easily damaged. For fluid media entrained with solid particles, the sealing structure of the soft seat valve is even more important. This is mainly due to the medium entrained with solid particles, it is very easy to be stuck in the valve flap and seat sealing surface, preventing the valve seat seal will cause leakage, and then due to high-speed media erosion so that the seat surface is Erosion damage. For the above-mentioned soft seat seal with secondary closure (Figure 6), there is no risk that such particles will get stuck between the valve disc and seat metal seal because there are also flaps and Sealing between soft seat, still can play a reliable and effective supplementary sealing effect. 3 Conclusion With the harsh conditions of the valve products continue to enhance the design of the valve structure requirements are also rising, but also to promote the development of engineering materials. Due to the special requirements of the valve, manufacturers are required to continuously develop a new type of seal components to meet the needs of the development of modern industry. The new single-seat control valve soft seal structure design can be successfully applied to the valve diameter of 25 ?, the pressure drop can reach 30MPa, with fire safety, reliable sealing, assembly, disassembly and maintenance features such as convenient, worthy of widespread promotion and application.