How is the stem of the Q41F ball valve prevented from flying off?

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Having been involved in ball valve design for so many years, the most common technical requirements I’ve seen for valves are fire resistance, anti-static properties, and protection to prevent the valve stem from flying off. Previously we discussed the fire (fire resistance) and anti-static properties of valves; today let’s talk about preventing the valve stem from flying off. Let’s first take a look at how valve stem anti-flight is described in the standard API 6D-2014. API 6D-2014, Page 23: “5.21 Stabilization of the stem The design of the valve must ensure that the stem is not forced out by internal pressure when the packing gland assembly and/or retaining elements are removed.” ” As described in the standards, what we commonly refer to as preventing the valve stem from moving abnormally is termed “fixing of the valve stem” in those standards (we will continue to use the term preventing the valve stem from moving abnormally in the following text). The purpose of this measure is to allow us, in the event that the packing is damaged and there is a leak at the valve stem, to remove the packing gland assembly and/or fixing elements while the valve is still under pressure, replace the damaged packing, and then reinstall the packing gland assembly and/or fixing elements in order to maintain sealing at the valve stem. If the valve stem cannot prevent flying, when a leak occurs at the valve stem, we are forced to stop the normal operation of the pipeline before replacing the packing, which will cause unnecessary disruptions to the proper functioning of the pipeline system. Now let’s talk about the various ways in which valve stems of ball valves are protected against flying 1. Reverse installation of the valve stem: http://cdn045.yun-img.com/static/upload/dsc86/news/20170915143525_51344.jpg. The reverse installation of the valve stem is generally used in floating ball valves; Figure 1 shows a typical floating ball valve with a valve stem installed in reverse. http://cdn043.yun-img.com/static/upload/dsc86/news/20170915143549_37800.jpg What is valve stem inversion? As shown in Figure 2, the valve stem is assembled outward from the cavity of the valve body. In this way, it effectively prevents the valve stem from being ejected by internal pressure, serving to prevent the valve stem from flying off. 2. Open-loop anti-flight mechanism: http://cdn057.yun-img.com/static/upload/dsc86/news/20170915143928_59235.jpg. The open-loop anti-flight mechanism is generally used on cast steel floating ball valves with small diameters (usually less than DN40/NPS 1 1/2), as in such cases the length of the valve stem is too great compared to the size of the valve body’s cavity, preventing the valve stem from being installed in reverse. Figure 3 shows a typical split-ring anti-flying floating ball valve. http://cdn035.yun-img.com/static/upload/dsc86/news/20170915143618_68329.jpg How does open-loop prevent flying? As shown in Figure 4, there is a groove at the lower end of the valve stem. The valve stem is inserted into the chamber from above the valve body; the split ring is separated from within the chamber and fits into the groove at the lower end of the valve stem. Then the valve stem is lifted upward until the split ring is locked in its retaining position within the valve body, preventing further upward movement of the valve stem. This effectively prevents the valve stem from being pushed out by internal pressure, thus serving to prevent it from flying out. 3. Packing gland anti-rotation mechanism: http://cdn057.yun-img.com/static/upload/dsc86/news/20170915144008_26265.jpg. This anti-rotation mechanism is generally used in fixed ball valves. Due to the structural characteristics of fixed ball valves, it is necessary to install the ball first and then the valve stem; as a result, methods such as installing the valve stem in reverse or using a split-ring design are not suitable for fixed ball valves. Figure 5 shows a typical stuffing box anti-flying fixed ball valve. As shown in Figure 6, after the valve stem is inserted from above the valve body and the gasket is placed in place, the packing box is then placed over the valve stem and screws are used to secure it. As long as these screws remain in place, the valve stem will not fly out. Next, packing is inserted into the packing box, along with the packing gland assembly. If the packing needs to be replaced, the packing gland assembly can be removed and the packing replaced directly. This approach effectively prevents the valve stem from being pushed out by internal pressure, thus serving to prevent the valve stem from flying out. Source: http://www. dsc86。 com/newsdetail_672950.html