a reversible motor operatively connected to {HEAD ~ said throttle valve} for operating {TAIL ~ said throttle valve} 
a reversible motor operatively connected to { HEAD ~ said throttle valve } for operating { TAIL ~ said throttle valve }
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL