The Stovepipe Damper: A Disc on a Shaft, Held by a Spring

"The nature of this invention relates to certain new and useful improvements in the construction of dampers for stove-pipes, and the object of the invention is to provide a damper the shaft of which is automatically secured to place by the spring of the damper-plate." When the shaft is pushed through, "the spring of the tongue compels the shoulder to engage with such socket, and the damper-plate is securely locked upon the shaft and beyond any possibility of its turning thereon." "In order to insure that the damper will remain in its adjusted position, I place a spring-plate, G, around the shaft. The ends of said spring, bearing against the outer wall of the pipe and exerting an outward pressure upon the handle, consequently draw the damper-plate into contact with the inner wall of the pipe and cause a sufficient friction to compel the damper to remain in the position to which it may be adjusted."

Cut a plywood disc 3 mm smaller than the inside of a length of PVC pipe. Drill across the pipe and pass a dowel through it and through a slot glued to the disc, so turning the dowel turns the disc. Mark angles on a card round the dowel's end with a protractor. Fix a box fan to blow into one end. At the other end measure the air speed with an anemometer at 0, 15, 30, 45, 60 and 90 degrees open. Plot the readings as a fraction of fully open and lay the notebook's curve over them.

**William Scully** of Detroit filed US 231,241 on 27 May 1880; it is dated 17 August 1880. He notes that slit-and-bent plates holding a shaft were already known, and does not claim that broadly. **Honest limits.** The patent gives no sizes. Pipe size, clearance, draught and gas density in the notebook are examples, and the flow model ignores the disc's own drag.