The stem is movable within the annular protrusion between at least a first position in which the orifice is closed when the valve stem first end sealingly abuts the protrusion extension sealing edge and a second position in which the orifice is open, the valve stem first end is offset from the protrusion extension and the valve stem is restricted from moving away from {HEAD ~ the valve body} by {TAIL ~ the groove} rear wall 
by
The stem is movable within the annular protrusion between at least a first position in which the orifice is closed when the valve stem first end sealingly abuts the protrusion extension sealing edge and a second position in which the orifice is open , the valve stem first end is offset from the protrusion extension and the valve stem is restricted from moving away from { HEAD ~ the valve body } by { TAIL ~ the groove } rear wall
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