An additional valve 408 for {HEAD ~ coolant flow} may be provided to control flow of {TAIL ~ coolant} only when the coring bit 104 is advancing 
An additional valve 408 for { HEAD ~ coolant flow } may be provided to control flow of { TAIL ~ coolant } only when the coring bit 104 is advancing
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH