向下的运动使气门向下移动离开气门座，气门被打开。
This downward movement forces the valve to move downward off its seat so that it opens.
当这发生时，气门弹簧紧紧地封闭气门口，叫做气门座。
As this occurs, valve springs pull the valve tightly closed against its opening, called the valve seat.
当这发生时，气门弹簧紧紧地关闭气门口，叫做气门座。
As this occurs, valve springs pull the valve tightly closed against its opening, called the valve seat.
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