Abstract: A counterbalancing mechanism for an articulated rolling door mounted for movement horizontally away from the doorway when the door is opened, with the weight of the vertical portion of the door producing variable forces urging the door towards its closed position as the door is moved between its open and closed positions. A drum is connected to the door and mounted for rotation in response to movement of the door between its open and closed positions, the drum having a spiral groove formed in the outer surface for guiding a cable along the drum when the drum is rotated. A cable is connected to the drum and adapted to wrap around the drum in the spiral groove in response to rotation of the drum in one direction, and to unwrap from the drum in response to rotation in the opposite direction. A weight is suspended from the cable for applying a torque to the drum, and thus applying a force to the door, urging the door toward its open position.

Abstract: A combination grill, air damper and fire damper is provided with a means for adjusting the volume of flow of air through the damper.

Abstract: The side curtains of a poultry house are automatically opened upon a power failure in the electrical circuit of the ventilating system. An electrical monitoring circuit activated responsive to such power failure, releases a winch which normally maintains the curtains in a closed position, causing them to drop to an open position. The electrical monitoring system includes a time delay relay which is activated upon the power failure to release a normally latched mechanism. A latching cable is thus released, freeing the winch.