When the device is subjected to {TAIL ~ the intake manifold vacuum}, the upper half of the elastic coating reacts by varying in {HEAD ~ size} to reflect the magnitude of the vacuum 
When the device is subjected to { TAIL ~ the intake manifold vacuum } , the upper half of the elastic coating reacts by varying in { HEAD ~ size } to reflect the magnitude of the vacuum
OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH