It relates to {TAIL ~ both the design} of the valve and to the method of {HEAD ~ its manufacture} 
It relates to { TAIL ~ both the design } of the valve and to the method of { HEAD ~ its manufacture }
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD