closure means covering said main valve means and secured to said main body and cooperating with them to provide an outer chamber to which said inlet pressure conduit leads, so as to exert {HEAD ~ pressure} on {TAIL ~ the opposite side} of said main valve means from said main valve chamber, 
on
closure means covering said main valve means and secured to said main body and cooperating with them to provide an outer chamber to which said inlet pressure conduit leads , so as to exert { HEAD ~ pressure } on { TAIL ~ the opposite side } of said main valve means from said main valve chamber ,
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