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Globe valve basic knowledge
Closing valve opening and closing pieces of plug-shaped flap, the sealing surface was flat or tapered surface, the valve flap along the fluid center line for linear motion. Stem movement form, lifting rod (stem lift, hand wheel does not lift), there are lifting rotary rod (hand wheel with the stem rotating together, the nut is located in the valve body). Globe valve only applies to fully open and fully closed, does not allow for regulation and throttling. Stop valves are forced to seal the valve, so the valve is closed, the pressure must be applied to the valve flap to force the sealing surface does not leak. When the medium from the bottom of the valve into the valve six, the operating force needed to overcome the resistance is the stem and packing friction and the pressure generated by the media thrust, off the valve force than the valve opening force, so the valve The diameter of the rod should be large, otherwise it will happen to the top of the valve stem failure. In recent years, since the self-sealing valve appears, the cut-off valve of the media flow to change over from the top of the valve into the valve cavity, then under medium pressure, the valve closing force is small, and open the valve force, the valve stem The diameter can be reduced accordingly. At the same time, in the medium, this form of valve is also more stringent. China's valve "three to" have provided that the flow of the valve, all from top to bottom. When the valve is open, the valve opening height, 25% to 30% of the nominal diameter, the flow has reached its maximum, indicating that the valve has reached the fully open position. Therefore, the full-stop position of the valve, valve stroke should be determined. Globe valve has the following advantages: 1, the structure is simple, more convenient manufacturing and maintenance. 2, small work schedule, opening and closing time is short. 3, good sealing, sealing surface friction, longer life expectancy. The shortcomings of the cut-off valve are as follows: 1, the fluid resistance, opening and closing the required force larger. 2, does not apply to the particles with a larger viscosity, easy to coking medium. 3, adjust the performance is poor. The type of stop valve by the position of the threaded stem is externally threaded type, the female type. By media flow points, there are straight-through, DC and angle. Globe valve by sealing form points, there are packing seal globe valve and bellows seal valve. Globe valve installation and maintenance should pay attention to the following: 1, handwheel, handle the operation of the globe valve can be installed in any position on the pipeline. 2, hand wheel, handle and Wei moving mechanism, do not allow lifting. 3, the flow of medium should be consistent with the arrow direction shown by the valve body.