An additional tubular insert member is held within {HEAD ~ the principal conduit member} to open and close {TAIL ~ the secondary conduit} connected directly to a work station 
to close
An additional tubular insert member is held within { HEAD ~ the principal conduit member } to open and close { TAIL ~ the secondary conduit } connected directly to a work station
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH