At {HEAD ~ the equilibrium position}, {TAIL ~ the vent} and vent follower are in direct relation to one another 
At { HEAD ~ the equilibrium position } , { TAIL ~ the vent } and vent follower are in direct relation to one another
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH