Closure of the first valve apparatus prevents fluid communication along the first flow path, whereby fluid communication may be diverted to the second flow path, provided {HEAD ~ the second valve apparatus} is in {TAIL ~ an open configuration} 
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Closure of the first valve apparatus prevents fluid communication along the first flow path , whereby fluid communication may be diverted to the second flow path , provided { HEAD ~ the second valve apparatus } is in { TAIL ~ an open configuration }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL