{HEAD ~ The valve} is opened and closed by {TAIL ~ means} of communicating bellows which are controlled by the pressure difference between two sections in the valve having different areas 
{ HEAD ~ The valve } is opened and closed by { TAIL ~ means } of communicating bellows which are controlled by the pressure difference between two sections in the valve having different areas
HEAD HEAD HEAD HEAD HEAD HEAD REL REL OTH OTH REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH