The needle valve dispenses fluid when {HEAD ~ the activator} acts on a piston, which shifts the spool or needle into {TAIL ~ the open position} 
The needle valve dispenses fluid when { HEAD ~ the activator } acts on a piston , which shifts the spool or needle into { TAIL ~ the open position }
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL