{HEAD ~ A pressure} of {TAIL ~ at least 20 psi} may be maintained within the chamber 10 
{ HEAD ~ A pressure } of { TAIL ~ at least 20 psi } may be maintained within the chamber 10
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH