The first and second valve apparatus may be used in conjunction with {HEAD ~ throttling apparatus} applied to one or both of {TAIL ~ the first and second flow paths} 
The first and second valve apparatus may be used in conjunction with { HEAD ~ throttling apparatus } applied to one or both of { TAIL ~ the first and second flow paths }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL