46 force while still ensuring a good reliable seal comparable prior art valves require 100 psi to close and 200 psi to open a pneumatically controlled valve whereas a pneumatically controlled valve of the present invention requires 40 psi to both open and close as valve 10 is closed manually valve handle 68 is rotated so as to cause stem 46 to advance valve seal 36 toward valve seat 34 as stem 46 moves into angled chamber 16 it pushes valve plug 38 ahead valve plug 38 is attached to stem 46 by stem flanged portion 42 when stem 46 is turned so as to open valve 10 retaining washer 44 makes stem flanged portion 42 captive in the recess seen in valve plug 38 because of retaining washer 44 and valve plug 38 moves away from valve seat 34 bellows 48 is soldered to valve plug 38 in a gas tight manner as is bellows 48 to backing plate 50 bellows 50 serves to isolate the stem 46 opening through the backing plate from the vacuum space which exists on the other side of bellows 48 in the event that bellows 48 might leak because of a crack in the bellows material threaded portion 60 is generally connected to a vacuum source so that any gas tending to fill the space between stem 46 and bellows 48 is removed by the vacuum source connected to threaded portion 60 bonnet 34 o 34 ring 52 and stem 34 o 34 rings 56 make the bonnet and stem assemblies gas.