When the solenoid is excited, {HEAD ~ the piston} is driven for {TAIL ~ movement} to switch a flow path within the housing 
is driven for
When the solenoid is excited , { HEAD ~ the piston } is driven for { TAIL ~ movement } to switch a flow path within the housing
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH