{HEAD ~ filter regulator} means for filtering the air entering the signal air path and for regulating {TAIL ~ the pressure} in the signal air path to a predetermined pressure 
{ HEAD ~ filter regulator } means for filtering the air entering the signal air path and for regulating { TAIL ~ the pressure } in the signal air path to a predetermined pressure
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH