Analysis of Sealing Force in a Bi-Directional Pressure Butterfly Valve
A bi-directional pressure butterfly valve primarily consists of a valve body, a disc (or butterfly plate), a stem, and a sealing ring. The eccentricity between the rotation center of the stem and the sealing surface plays a crucial role in the valve's performance. During forward flow, the stem applies a necessary sealing force, FMF (in Newtons), to the disc’s sealing surface. However, due to the influence of the medium force, FMJ (in Newtons), the actual sealing force on the surface increases to FMZZ. This means that FMZZ is the sum of both FMF and FMJ.
When it comes to reverse sealing, the force exerted by the stem on the disc’s sealing surface is even greater than during forward sealing. This increased force can lead to more significant deformation of the stem, especially when the medium flows in the opposite direction.
Analysis of the Impact of Stem Bending Deformation on Sealing
Since the stem experiences higher forces during reverse flow, the effect of its bending deformation on the sealing performance is mainly analyzed in this scenario. When the medium flows backward, the stem must overcome the resistance from the sealing surface as well as the positive pressure exerted by the fluid. As a result, the stem behaves like a simple beam under load.
Under the combined influence of the sealing force and the medium force, the stem may bend. During forward flow, the stem bends toward the sealing surface, which actually enhances the sealing effect. However, during reverse flow, the stem bends away from the sealing surface, causing the disc to move away as well. This reduces the sealing force and compromises the seal. Therefore, the valve may not provide reliable sealing when the medium flows in the reverse direction. To address this issue, a new type of bi-directional metal-sealed butterfly valve has been developed.
In this improved design, the upper and lower wedge shafts are positioned at the top and bottom of the valve cavity. The cross-sectional area of these wedges is increased, thereby increasing the moment of inertia (I) and enhancing the stiffness of the stem. This reduces the deformation amount (δ2) without significantly increasing fluid resistance. Additionally, if the clearance between the wedge shaft holes and the stem is equal to or larger than δ2, the wedges will not cause the stem to bend.
The upper and lower wedges also apply additional wedge force to the stem, increasing the sealing force on the disc. This helps compensate for any minor displacement caused by the deformation, improving the reliability of the reverse sealing.
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