Corliss' design provided a means of adjusting the point in the power stroke of the engine’s piston at which high pressure steam being fed to the cylinder was cut off. This was desirable as power was extracted from the expansive force of the steam after the valve closed. This saved fuel by avoiding continuous use of high pressure steam.
Corliss' major innovation was that the connections from the steam inlet valve push rods to the valve port cranks were not permanent. The details of his design can be seen in the upper left of the image of the model. Each crank had a "toe" that was engaged by a hook on its respective pushrod. A spring held against the pushrod caused the toe and hook to remain engaged. The worm gear shown on the left of the model allowed adjustment of rods that would move so as to apply pressure to the pushrods overcoming the force of the springs, thereby causing the toe and hook to disengage To assure the steam valve ports closed properly with the hook and toe disengaged, Corliss provided a heavy weight to pull the crank arms down. The weight and its connected rod are shown at the extreme left of the image. Changing the number of turns of the worm gear varied the point in the cycle where the pushrods would disengage. This allowed the timing of cut off to be varied as dictated by the operating conditions of the engine at the time.
Corliss was a prolific inventor of steam technology in the middle 1800s and was the founder of the Corliss Steam Engine Company. His engines were used worldwide, and his designs were adopted by other engine manufacturers.
The patent model is constructed of brass and mahogany. All of the key elements of the patent are illustrated by the model. The image of the rear side of the model shows the steam and exhaust valve operation. Diagrams showing the complete design of the patent can be found in the patent document online at the United States Patent and Trademark Office website, www.uspto.gov.