With power off to the dryer, both towers pressurize to line pressure. The N.C., 2/2 solenoid valves are both de-energized. Air pressure on the outside of the diaphragm
increases as air flows through the tiny bleed hole in the diaphragm. The air pressure on the outside of the diaphragm quickly equalizes with the internal air pressure of
the dryer allowing the small spring on the outside of the diaphragm to press the diaphragm against its seat, keeping air from exiting the silencer.
Note: Any air flowing through the dryer, passes through both towers.