These small valves are used to accurately regulate the flow of fluids and {HEAD ~ gases} at {TAIL ~ certain flow rates} 
at
These small valves are used to accurately regulate the flow of fluids and { HEAD ~ gases } at { TAIL ~ certain flow rates }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL