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