其它类型的设计则在中间有一个圆形的剪切块，使其适合井眼内管柱的直径以便当管柱位于井眼内时能够密封井眼。
Other designs have a circular cutout in the middle that corresponds to the diameter of the pipe in the hole to seal the well when pipe is in the hole.
这些管柱闸板有效地密封了有限范围内的管柱直径。
These pipe RAMS effectively seal a limited range of pipe diameters.
大直径的液压缸，通常是收缩，迫使闸板的两半一起向中间运动去密封井眼。
Large-diameter hydraulic cylinders, normally retracted, force the two halves of the cover together in the middle to seal the wellbore.
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