Fluid returning to the surface passes through mud return line 14 via {TAIL ~ various surface equipment components} as known to those skilled in the art, and then into {HEAD ~ the mud pits}, thereby completing the closed loop 
Fluid returning to the surface passes through mud return line 14 via { TAIL ~ various surface equipment components } as known to those skilled in the art , and then into { HEAD ~ the mud pits } , thereby completing the closed loop
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH