自来水放水时,水管为什么会咚咚作响?

自来水放水时,水管为什么会咚咚作响?
自来水管里有空气,水管中的压力又较大,空气与水在压力的作用下一起流动,就会碰撞自来水管管壁,发出咚咚声。消除这种声音只要把水多放一会儿就行了。
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