In the rotary version, {HEAD ~ the vent follower} operates in {TAIL ~ a wiper type fashion} 
operates in
In the rotary version , { HEAD ~ the vent follower } operates in { TAIL ~ a wiper type fashion }
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL