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.

如果要用大尺寸阀门需要采用倒旋塞结构，就是旋塞大头朝下，这样不可避免的在重力作用下，密封效果会降低，只好采用注脂的方式密封，注入的润滑脂导致这种阀门只能用于天然气、石油的储存和运输，而不能用于其它行业，因为润滑脂会污染介质。

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.

而良工球阀虽然密封效果理论上稍差，但是可以做成很大口径，而且随着加工精度、密封材料的改进，球阀的密封效果已经可以很好的满足实际应用要求，而且应用范围更广。

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.