| 摘要 |
<p>A conduit with inlet and discharge ends respectively for receiving a supply of air under pressure and for delivering the air at a lower pressure has a cylindrical configuration and an eliptical butterfly type damper is disposed diagonally therein. The damper turns about an axis intermediate its diagonally opposite ends and the oncoming air stream thus impinges on the upstream face of the damper on opposite sides of the axis and creates a differential force, the said differential force tending to close the damper and constituting a first closing force. A second closing force for the damper is provided by a small bellows supplied with air through a small conduit from the downstream side of an orifice member disposed in the main conduit upstream of the damper. A second and substantially larger bellows serves to open the damper and a small conduit connects the said bellows with a controller supplied with air from an upstream side of the orifice member in the main conduit. The controller regulates pressure in the large bellows as determined by a pressure drop signal across the orifice member and a thermostat. The thermostat vents air from the controller to reduce large bellows pressure for damper closing operation and, conversely, the large bellows is pressurized to cause the butterfly damper to move in the opening direction.</p> |
