{HEAD ~ A third vacuum pump}, connected to {TAIL ~ the processing chamber}, is operated when the vacuum in the processing chamber reaches a predetermined value 
connected to
{ HEAD ~ A third vacuum pump } , connected to { TAIL ~ the processing chamber } , is operated when the vacuum in the processing chamber reaches a predetermined value
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH