The vent hole is closed by {HEAD ~ the base plate} of the fixed scroll member for the majority of {TAIL ~ its operational cycle} 
The vent hole is closed by { HEAD ~ the base plate } of the fixed scroll member for the majority of { TAIL ~ its operational cycle }
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL