When there is no mechanical actuation, compressed air, supplied from the main, passes through connection 1 into chamber 9 and further through channels in valve member 4 into valve outlet chamber 2 (Fig. a). When rubber membrane 5 is pressed, plunger 6 is pushed downward. At first, the annular projection of the plunger runs up against rubber insert 7 of valve member 4, disconnecting chambers 9 and 2. At this time, bushing 8 is held in its upper position by the pressure of air acting on its lower end. Upon further motion of membrane 5, disk 13 presses bushing 8 downward so that rubber insert 10 is pushed off its seat. At this, chamber 2 is connected through the longitudinal slots in bushing 8 to chamber 3, which is connected to the atmosphere. When membrane 5 is released, plunger 6 and valve member 4 are returned to their initial positions by springs 11 and 12. The principle of the valve is shown schematically in Figs. b and c.
$3686$SHP,FC$