Additionally, the housing 12 includes an inlet 15 for receiving {HEAD ~ an assist gas}, which is typically {TAIL ~ air} 
Additionally , the housing 12 includes an inlet 15 for receiving { HEAD ~ an assist gas } , which is typically { TAIL ~ air }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL