The other of the further chambers contains a second electro magnetic control valve fed both by said D.C. voltage and by a pulsed voltage, and operable to control both an orifice through which the first chamber communicates with atmosphere and an orifice through which {HEAD ~ the first chamber} communicates with {TAIL ~ a source} of gas at sub atmospheric pressure 
The other of the further chambers contains a second electro magnetic control valve fed both by said D.C. voltage and by a pulsed voltage , and operable to control both an orifice through which the first chamber communicates with atmosphere and an orifice through which { HEAD ~ the first chamber } communicates with { TAIL ~ a source } of gas at sub atmospheric pressure
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH