The slight reduction in the diameters of portions of the valve may be characterized as somewhat of a collapsing motion which can occur around the distal end of the lid seal post 502 and which further facilitates {HEAD ~ the sealing} of the valve 345 by {TAIL ~ the lid seal post} 502 
The slight reduction in the diameters of portions of the valve may be characterized as somewhat of a collapsing motion which can occur around the distal end of the lid seal post 502 and which further facilitates { HEAD ~ the sealing } of the valve 345 by { TAIL ~ the lid seal post } 502
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