This is also important when {TAIL ~ the operator} is not in {HEAD ~ a position} to physically observe whether or not he has effectively closed the valve 
This is also important when { TAIL ~ the operator } is not in { HEAD ~ a position } to physically observe whether or not he has effectively closed the valve
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH