In {TAIL ~ an equilibrium position}, {HEAD ~ the vent} is closed off by the vent follower 
In
In { TAIL ~ an equilibrium position } , { HEAD ~ the vent } is closed off by the vent follower
REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH