A vent hole in {TAIL ~ the wrap} of the orbiting scroll member cyclically moves over {HEAD ~ the two grooves} 
A vent hole in { TAIL ~ the wrap } of the orbiting scroll member cyclically moves over { HEAD ~ the two grooves }
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD