When there is no mechanical actuation, compressed air, supplied from the main, passes through connection 1 into chamber 9 (Fig. a). Chamber 2, the valve outlet, is connected to chamber 3 which is connected to the atmosphere through holes and a central channel in bushing 4. When rubber membrane 5 is pressed, plunger 6 is pushed downward. At first, rubber insert 10 closes off the central channel in bushing 4, disconnecting chambers 2 and 3. Upon further motion of the plunger, it shifts bushing 4 downward so that rubber insert 11 is pushed off its seat. At this, compressed air from chamber 9 passes into valve outlet chamber 2. When membrane 5 is released, bushing 4 and plunger 6 are returned to their initial positions by springs 8 and 7. The principle of the valve is shown schematically in Figs. b and c.
$3685$SHP,FC$