Movement of the shaft and {HEAD ~ vent} follower continues until the pressure between the two cells is equalized and the vent follower is once again in direct relation to {TAIL ~ the vent} 
Movement of the shaft and { HEAD ~ vent } follower continues until the pressure between the two cells is equalized and the vent follower is once again in direct relation to { TAIL ~ the vent }
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL