One of the further chambers contains a first electro magnetic control valve fed by a D.C. voltage, and operable to control {TAIL ~ an orifice} through which {HEAD ~ the first chamber} communicates with atmosphere 
through communicates
One of the further chambers contains a first electro magnetic control valve fed by a D.C. voltage , and operable to control { TAIL ~ an orifice } through which { HEAD ~ the first chamber } communicates with atmosphere
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL REL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH