Operating principle and structural characteristics of eccentric semi pneumatic ball valve Dual eccentric semi pneumatic ball valve is applicable to transport media with precipitation, scaling and crystallization in petroleum, chemical, gas, metallurgy, power, steel and paper industries. The eccentric semi pneumatic ball valve uses the eccentric wedge principle to achieve self-locking positioning and reliable sealing. Double eccentricity means that there is a relative radial eccentricity E between the center of the valve stem and the center of the valve channel, and there is a relative axial eccentricity e between the center of the valve sealing surface and the center of the valve stem (i.e. the center of rotation of the valve disc), and E=2e. The wedge angle changes on the circular eccentric and its development plane. The working principle and structural characteristics of the eccentric semi pneumatic ball valve adopt the forced sealing structure. When tightening the middle flange bolt, apply a compression force to the sealing gasket, the preloaded gasket is compressed, and the uneven micro gap on the sealing surface is filled, thus forming the initial sealing condition to prevent medium leakage - the preloaded specific pressure is formed on the sealing surface. When the medium pressure rises and the valve is opened and closed, the preload specific pressure on the sealing surface drops and the gasket rebounds. If the gasket has enough capacity to make the working seal specific pressure on the sealing surface always greater than the medium and the opening and closing specific pressure, and a certain margin is left, the sealing surface will maintain a good sealing state. Therefore, the necessary condition for forced sealing is that under the effect of medium pressure and opening and closing, a certain residual compression force can still be maintained on the sealing surface. Of course, it is also limited by the maximum pressure that the sealing pair material can withstand, that is, the allowable specific pressure [q] should meet qMF q.

Working principle and experiment of maintenance free rotary compensator
The application of maintenance free rotary compensator and rotary compensator products relies on the flexible packing in the packing chamber to stop sealing. During the application of the product, the packing will wear a little every time it rotates. When the wear reaches a certain value, the product will leak. The maintenance free rotary compensator has added a set of springs above the packing compression flange. When the packing shows slight wear, it will be compensated by the tension of the compression spring, thus extending the leakage time of the product (the leakage time is delayed by 3-5 years). When the amount of wear exceeds the amount of spring tension compensation, it is only necessary to tighten the nut above the spring compression flange. There is no need to stop air for repair. There is no limit on the number of operations, and leakage is not easy to occur, thus greatly improving the social and economic benefits of gas supply units and gas users. The product will not leak after 5000 times of compensation under the pressure of 4.0Mpa, and the sealing effect is excellent.
Characteristics of maintenance free rotary compensator
The sealing packing of the maintenance free rotary compensator adopts the most advanced packing in China at present, which has a temperature resistance of - 60 ℃ - 800 ℃. Since there is a retaining ring welded on the outside of the inner sleeve and the inside of the outer sleeve of the compensator, a ball (rolling ring) to reduce friction is installed between the two retaining rings, reducing the wear of the inner sleeve on the sealing packing. Moreover, since the natural tension of several groups of springs installed on the compensator pushes and presses the packing gland flange, the sealing packing with extremely slight wear will always be in a compact state, so that the liquid in the pipeline or the gas medium of the compensator will not leak. When the wear of the packing is large, the spring tension cannot meet the adjustment, The external force can be used to compress and stop the adjustment of the spring so as to achieve the required sealing effect without stopping the work. Therefore, this product overcomes the lack of other similar products. The original rotary and sleeve compensators cannot be compensated and adjusted in time when the packing is worn, which causes the sealing performance of the compensator to decline until leakage occurs, In addition, the product must be removed from the pipeline to turn over the filler after the filler wear is large, which affects the operation of the pipeline and the normal consumption of users.
After the device is installed, check whether the gland bolts can be tightened evenly (not too tight, just average), and then stop the sectional water pressure seal test. Before passing the test, stop the system pressure test. The test can be 1.5 times of the working pressure or stop the pressure test according to the data request provided by the design department. The test will be stopped three times:
The first time: increase the pressure to 1/3 of the working pressure, close the water filling valve, and check whether there is water dripping. If there is leakage, please tighten it slightly to stop the leakage; The second time: boost the pressure to the working pressure, stop boosting and check whether there is leakage; The third time: increase the pressure to 1.5 times the working pressure, and after 10 minutes, if the pressure remains unchanged, the strength test is qualified. When the pressure drops to the working pressure again, it lasts for 30 minutes. If the pressure remains unchanged, it is qualified.