The stem is axially movable within {TAIL ~ the annular protrusion} between at least a first position in which the orifice is closed when {HEAD ~ the valve} stem first end sealingly abuts the valve seat and a second position in which the orifice is open when the valve stem first end is offset from the valve seat 
The stem is axially movable within { TAIL ~ the annular protrusion } between at least a first position in which the orifice is closed when { HEAD ~ the valve } stem first end sealingly abuts the valve seat and a second position in which the orifice is open when the valve stem first end is offset from the valve seat
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