Abstract: A control system for a bypass duct includes a pneumatic damper control assembly, a sensor and a pneumatic switch. The damper control assembly includes a damper vane mountable in the bypass duct for movement between relative open and closed positions to regulate airflow through the bypass duct. The position of the damper vane is controllable via pressure applied through a damper control line. The sensor is mountable to the supply duct to transmit a pneumatic supply duct signal via a supply line based on at least one of air pressure or air velocity in the supply duct. Finally, the pneumatic switch opens or closes the connection between the damper control line and the supply line based on the difference between (1) the pneumatic supply duct signal via the supply line, and (2) the combination of the pneumatic pressure from the damper assembly and a switch biasing pressure.

Abstract: A fluid flow control damper assembly having a damper vane and a piston actuator is relatively easy to install when the outer surface of a duct is inaccessible. The piston actuator includes a powder metal piston, lacking an elastomeric (for example, rubber) seal, that is closely received within a glass cylinder. The glass cylinder has a fitting that closes one end of the cylinder and is connectable to a pneumatic control system. A drive rod is connected between the piston and the damper vane to move the damper vane between an open position and a closed position.