Eccentric Half Ball Valve body and valve core rotation center (i.e. valve stem axis) are offset by a radial dimension from the geometric center of the sealing sphere of the valve core, and there is also an offset dimension on the valve body channel axis with the sealing surface of the electric control valve seat. The sealing pair is in contact with metal under the action of external force. The pneumatic control valve realizes self-locking closing by relying on two eccentricities. The reasonable selection of eccentricity makes the self-locking angle less than the friction angle, If the self-locking angle is too small, it is easy to close and difficult to open. If the angle is too large, although the opening force is small, the closing torque increases rapidly. After repeated tests on the test bench, it is very important to determine the reasonable eccentricity of the two collocations. The reliable self-locking performance ensures its tight sealing. This is the core technology of hemispherical valve. In terms of structural principle and manufacturing means to achieve the best seal, ball valves, butterfly valves, gate valves, globe valves and so on are inferior.
The sealing between the valve core and the valve seat is spherical line contact, which realizes self-locking by eccentricity. The sealing pair hardly contacts in the whole process of opening and closing. Only at the moment of opening and closing, it contacts and brakes tightly to achieve zero leakage, so as to ensure that there are no leakage points at the dynamic and static seals. During the process of contacting the valve seat, the valve core has the ability to strongly remove the scaling or other deposits on the valve seat. During the frequent reciprocating motion of the opening and closing of the sealing surface of the gate valve, the mixed flow medium scales and precipitates in the lower cavity of the valve body. The stop valve completely relies on positive pressure to seal, and the scaling on the valve seat has no cleaning ability. The frequent repeated wear of the two packing is easy to cause the internal leakage and external leakage of the gate valve and stop valve. The sealing of ball valve depends on the long-term extrusion of the valve seat on the spherical surface. It must wear faster than the hemispherical valve. The sealing of butterfly valve is mediated by rubber, which is far from the metal hard sealing performance of hemispherical valve, ball valve and gate valve. After long-term use of the hemispherical valve, the valve seat will also produce a small amount of wear. It can continue to be used through adjustment. During the opening and closing process of the valve rod and packing, the valve rod only needs to rotate 90 °. When there is a sign of leakage, press a few bolts of the packing gland to achieve no leakage at the packing. However, other regulating valves are still reluctantly used with small leakage, and the regulating valve can be replaced with a large leakage. Aluminum Corporation of China Guangxi Branch (working medium: red mud solution, strong alkali solution) said in the use report that "... The control valve is easy to operate (open and close), simple to maintain, good sealing performance, and has a long service life compared with ordinary gate valves,... Since its use in July 2001 (has been working for nearly three years - editor), no mechanical problems and leakage problems have been found, and it is very popular in terms of labor intensity, energy saving and leakage".
During the whole process of opening and closing the hemispherical valve, the sealing pair is almost in the undamped idling state, and the external force is only disengaged or compressed at the moment of opening and closing, while the valve rod only needs to rotate by 90 °, which is light and fast, of course, the operation is light. In the process of opening and closing, the ball valve operates under the holding force of the valve seats at both ends. Its opening and closing torque is larger than that of the hemispherical valve. The larger the nominal diameter is, the more obvious the difference between the opening and closing torque is. The opening and closing of the butterfly valve is realized by overcoming the deformation of the rubber, and the torque is larger. The operation time of gate valve and stop valve is long and laborious.
Long service life
The sealing pair is a kind of bimetal, which is overlaid with alloys for different purposes on the matrix. After special heat treatment, its mechanical properties and physical and chemical indexes reach the best state to meet the needs of different working conditions (media such as strong wear, rapid scouring, serious corrosion, etc.). The hardness of the valve seat of the regulating valve is slightly lower than that of the valve core, with different materials and heat treatment processes. When necessary, the hardness of the sealing pair can reach more than HRC 53, and it can withstand 560 ℃ high temperature. Practice has proved that its anti-corrosion and anti seizing ability is 6 times that of stainless steel sealing pair. The regulating valve can be opened and closed for tens of thousands of times without failure, extending its service life. Wuhan Iron and steel company is using the report to say: "When purchasing your company's manual, electric and pneumatic hemispherical valves in the bituminous coal injection phase I project, there was no ash deposition during use, the switches were flexible, and the sealing performance was good. Among them, the hemispherical valves used in the main line were well matched with the imported foreign equipment, and the price of all kinds of regulating valves was only 15-20% of the price of similar foreign equipment, saving investment for the bituminous coal injection phase I project of WISCO,... It has been used for nearly three years, in good condition, and saving." Cost, reduced equipment failure, reduced labor intensity of workers, and was unanimously praised by the leaders and managers of the iron plant. ".
Eccentric Half Ball Valve are widely used in non-ferrous smelting, coal injection and dust removal of gas, steel and iron, power slag transportation, smelting and transportation of harmful gases (hydrogen sulfide, phosgene, etc.) and oil products (heavy oil, crude oil, residue, etc.). The reason why it is widely used is that the sealing pairs are overlaid with different alloys to make them bimetallic. The main parts such as valve body and valve rod adopt the required materials to meet different working conditions,