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