The operation method 5, {TAIL ~ wherein the first valve} and the second valve are {HEAD ~ a control valve} 
The operation method 5 , { TAIL ~ wherein the first valve } and the second valve are { HEAD ~ a control valve }
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD