Preferred valves can be {HEAD ~ skirt valves}, which possess {TAIL ~ numerous advantages} over known one way valves such as umbrella valves and duckbill valves 
possess
Preferred valves can be { HEAD ~ skirt valves } , which possess { TAIL ~ numerous advantages } over known one way valves such as umbrella valves and duckbill valves
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH