Doubts regarding the calculation of the seal surface force on the seat of soft-sealed floating ball valves
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I’m having trouble calculating the force on the valve seat sealing surface. I hope those who know more can give me some guidance; thank you. According to the valve design manual, the total force acting on the valve seat seal is given by FMZ = FMJ + FMY. The angle between the sealing surface and the normal to the pipeline’s centerline is φ, and the normal pressure exerted by the ball on the sealing surface is N = FMZ / cosφ. I think this isn’t correct; after analyzing the forces acting on the ball, it seems that FMZ should be the resultant force of N and the reaction force from FTP. Therefore, N should be FMZ · cosφ. I searched online for design books, but they all state that N = FMZ / cosφ, which has left me confused. I’m starting to doubt life now: Q, with the guidance of those experienced experts who understand this
Why is Ftp tangential? I think the issue lies here. If we consider a soft seal, then taking into account the reaction force exerted by the valve seat, the resultant force in both horizontal and vertical directions should equal the reaction force of N. The horizontal component should be equal to FMZ. Therefore, N = FMZ/cosφ
FTP is the static friction force between the sphere and the soft-sealed valve seat; its direction is always perpendicular to the normal force N, and its value is directly proportional to this normal force. Since the normal force is very large, the value of the static friction force FTP cannot be ignored. Since forces act in pairs, analyzing the forces acting on a sphere is much simpler. Analyzing the forces acting on the valve seat directly seems a bit complicated. As shown in the figure below, there are separate analyses of the forces acting on the sphere and the valve seat. For the sphere, the resulting value is N=FMZ·cosφ; however, while an analytical relationship can be established for the forces acting on the valve seat, no numerical value can be calculated. FMZ represents the resultant force of the medium’s push on the sphere and the preloading force (both forces act horizontally to the right, assuming that the center of the valve’s flow channel is horizontal). The force transmitted from FMZ to the valve seat is not horizontal; therefore, FX (the elastic force exerted by the valve seat’s support surface on the valve seat) is not equal to FMZ. In fact, FMZ transmits its force to the valve seat in the form of a normal force N and a static friction force FTP. Thus, the statement that “the horizontal component should equal FMZ” is incorrect, and as a result, it is impossible to derive N=FMZ/cosφ.
FTP is the static friction force between the sphere and the soft-sealed valve seat; its direction is always perpendicular to the normal force N, and its value is directly proportional to this normal force. Since the normal force is very large, the value of the static friction force FTP cannot be ignored. Since forces act in pairs, analyzing the forces acting on a sphere is much simpler. Analyzing the forces acting on the valve seat directly seems a bit complicated. As shown in the figure below, there are separate analyses of the forces acting on the sphere and the valve seat. For the sphere, the resulting value is N=FMZ·cosφ; however, while an analytical relationship can be established for the forces acting on the valve seat, no numerical value can be calculated. FMZ represents the resultant force of the medium’s push on the sphere and the preloading force (both forces act horizontally to the right, assuming that the center of the valve’s flow channel is horizontal). The force transmitted from FMZ to the valve seat is not horizontal; therefore, FX (the elastic force exerted by the valve seat’s support surface on the valve seat) is not equal to FMZ. In fact, FMZ transmits its force to the valve seat in the form of a normal force N and a static friction force FTP. Thus, the statement that “the horizontal component should equal FMZ” is incorrect, and as a result, it is impossible to derive N=FMZ/cosφ.
Think about the wedge-type force-amplifying mechanism and you’ll understand
Senior, could you explain it in more detail? I’m not majoring in mechanics, so I don’t understand
Your force analysis is based on a single point on the sphere, rather than the entire structure; the analysis of the whole structure is carried out using the theory of wedge-shaped inclined planes