Features of soft-sealed plug valves

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The features of soft-seal plug valves are reflected in aspects such as the valve body, the plug, stem sealing, sealing in the line direction (internal leakage), the sealing between the plug and the sleeve in the line direction, and the adjustment of sealing in the pipeline direction, as detailed below. 　　1. Valve body The valve body has been redesigned; reinforcement ribs are provided at the junction where the flange meets the valve body as well as at the bottom of the valve body, thereby enhancing its strength and extending its service life. 　　2. Plug: The plug of the valve core is a 2-degree plunger; for the same valve size, it is nearly twice as large as those produced by other manufacturers. This results in a larger sealing area, a longer service life, and higher flow capacity (i.e., a higher rated Cv value for the same valve size). 　　3. Stem Sealing A 360-degree contact over a large area between the upper part of the plug port and the PTFE sleeve forms the first layer of sealing. 　　The second seal is a uniquely designed PFA sealing diaphragm. 　　The unique design of the PFA reverse-lip diaphragm allows, when the pressure beneath the diaphragm becomes too high, for that pressure to act on the reverse-lip diaphragm and compress the valve stem, thereby providing a reinforced dynamic seal; at the same time, under compression, the reverse-lip diaphragm presses tightly against the valve stem to create a static seal. 　　Diaphragm material: For unique sealing structures, achieving good sealing performance is closely related to the material used for sealing. The diaphragm material used is PFA, whereas most manufacturers use PTFE. PFA has the following advantages: better elasticity than PTFE; better wear resistance than PTFE; stronger resistance to permeation than PTFE; good memory properties, resistance to creep, no cold flow, and it returns to its original shape (this property is particularly well demonstrated and effective in acetic acid production facilities). ) 4. Online directional (internal leakage) sealing: The tightly fitted conical valve plug, in combination with the PTFE sleeve, creates a tight seal. The sleeve surrounds the valve plug opening, tightly enclosing the upper and lower parts of the plug to eliminate any voids and achieve a two-way seal. 　　The sealing is completely independent of pipeline pressure; there is no metal-to-metal contact, ensuring a tight seal. The valve can rotate freely without the need for lubrication. The sealing can be adjusted online, eliminating the need to remove the valve from the pipeline during maintenance. The skirt at the contact point between the valve plug and the sleeve provides a self-cleaning effect, which helps to remove impurities from the fluid and prevents damage to the valve plug and the sleeve – making it suitable for applications involving slurries. 　　5. On-line, in-line sealing adjustment of the valve plug and sleeve. The advantage of plug valves is that, after the valve seat has worn out over time, it is possible to lower the conical valve plug to create a new sealing surface, and this can be done while the pipeline is under pressure, thereby saving maintenance time and reducing costs. It differs significantly from conventional adjustment methods: Conventional methods use three bolts to adjust downward, thereby pressing the valve plug down and creating a new sealing surface. This adjustment method requires even adjustment of the three bolts, which is difficult to achieve in practice. If the adjustment is uneven, the plug will tilt to one side, causing damage to the valve seat during closure; at the same time, the seal of the valve stem will also be damaged, and the torque required to operate the valve increases. This leads to internal leakage and external leakage of the valve stem. 　　The adjustment mechanism that uses a cylindrical cross-section in contact with a flat surface is a patented design for rocker arm adjusters, whereby the valve plug is adjusted downward using two bolts. Since the contact surface between the rocker arm adjuster and the thrust collar is tangential, the adjustment system requires only two bolts; tightening either bolt applies a uniform vertical downward force on the gland, thereby preventing the plug from shifting and enhancing the sealing effect as well as extending its service life. After adjustment, a tight seal can be achieved again.