When the valve activator stops, a spring force shifts {HEAD ~ the spool} or needle to {TAIL ~ the closed position} 
to
When the valve activator stops , a spring force shifts { HEAD ~ the spool } or needle to { TAIL ~ the closed position }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL