When {TAIL ~ the vent follower} is caused to move {HEAD ~ the power transfer shaft} also moves accordingly 
When { TAIL ~ the vent follower } is caused to move { HEAD ~ the power transfer shaft } also moves accordingly
OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH