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