Compared with other valves, the Triple Eccentric Butterfly Valve has the advantages of good sealing performance and long service life. However, because the sealing surface of the Triple Eccentric Butterfly Valve is oblique cone, it can only achieve one-way pressure sealing, which limits the application of the Triple Eccentric Butterfly Valve.
Through analysis, the processing technology and matching tolerance of parts and components are improved, so that the three-eccentric metal hard-sealed butterfly valve achieves two-way zero leakage. The specific methods are as follows:
1. Valve body processing

Stem holes in the butterfly disc of three eccentric metal hard seal butterfly valves and the stem holes in the valve body are usually machined in a boring machine. In order to reduce the coaxiality error, the dial gauge is placed on the spindle after the fixture and the valve body are installed in place. The dial of the valve body is symmetrical along the central line of the spindle by rotating the spindle. After boring one end of the hole, the dial gauge is used to correct the other end of the passage after the fixture table rotates 180 degrees.

2. Disk Plate Processing
Tri-eccentric metal hard sealing butterfly valve sealing surface generally adopts a combination of sealing rings, the structure is "metal + graphite" and "metal + PTEE" and so on. When processing the sealing surface, the plate, the sealing assembly and the ring are assembled together, and the sealing surface is machined to size on the inclined die. If the "metal + graphite" sealing assembly is overprocessed, the graphite is replaced by the metal process sealing ring. If processing "metal + PTEE", PTEE is easy to deform, affecting the seal, so when processing, reserve 0.8 to 1 mm processing allowance for the sealing surface of disc plate, seal assembly and ring assembly according to the size of reference paper, so that there is room for adjustment even if there is deformation in assembling PTEE.
3. Tolerance Selection of Sealing Pair
When the seal assembly is a "metal + PTFE" structure, there is no leakage at the seal during pressure testing, but when the pressure is released, the larger the caliber, the higher the pressure, the more obvious the phenomenon is. The problems mentioned above occur again after loosening the screw of the compact sealing assembly and re-compacting the pressure test. The reason is that with the increase of sealing pressure during pressure test, the sealing assembly is forced to shrink, and the PTFE sealing ring can not be restored to its original state due to the tightening of screw during pressure relief, resulting in leakage. Due to the restriction of butterfly valve structure, the method of increasing the length and number of screw can not be used to improve the compression force.
Considering from the design point of view, the matching tolerance between seal assembly and butterfly plate is dll/Dll. We can change PTFE seal ring inner diameter tolerance to Js9, butterfly plate positioning step tolerance to h9, and for easy assembly, metal seal ring inner diameter tolerance is still D11. After the change of fitting tolerance, the clearance between PTFE sealing ring and butterfly plate is small, which restrains the compression and internal contraction. At the same time, when the pressure is released during the valve detection process, the leakage of the valve seal is also solved.
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