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