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