When used for cut-off, the plug valve has slightly better adjustment ability than the Lianggong ball valve, but its advantages are limited. Although the sealing surface of the plug valve is much larger than the ball valve and has good sealing effect, it also brings the defects of too large torque and inflexible action. The conventional positive plug structure is difficult to achieve a large diameter due to the influence of the weight of the plug.

如果要用大尺寸閥門需要采用倒旋塞結構，就是旋塞大頭朝下，這樣不可避免的在重力作用下，密封效果會降低，只好采用注脂的方式密封，注入的潤滑脂導致這種閥門只能用于天然氣、石油的儲存和運輸，而不能用于其它行業(yè)，因為潤滑脂會污染介質。

If you want to use a large-size valve, you need to use the inverted cock structure, that is, the big end of the cock is facing down, so it is inevitable that the sealing effect will be reduced under the action of gravity, so you have to use grease injection for sealing. The injected grease causes that this valve can only be used for the storage and transportation of natural gas and oil, not for other industries, because the grease will pollute the medium.

而良工球閥雖然密封效果理論上稍差，但是可以做成很大口徑，而且隨著加工精度、密封材料的改進，球閥的密封效果已經(jīng)可以很好的滿足實際應用要求，而且應用范圍更廣。

Although the sealing effect of Lianggong ball valve is slightly poor in theory, it can be made into a large diameter. With the improvement of machining accuracy and sealing materials, the sealing effect of ball valve can well meet the requirements of practical application, and the application range is wider.