Wiegand's 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 continuing use of high pressure steam. Wiegand provided a means of adjusting the point of cut-off while the engine was running. This was not new; others such as B. H. Wright and George Corliss had patented devices to do so. Both Wiegand and Wright based their designs on variable eccentrics. In a variable eccentric, the amount of eccentricity, or offset from the shaft center, can be varied by a control mechanism.
The method to accomplish this consisted of an inclined metal slide that varied the amount of eccentricity as a lever was moved causing the slide to move through a slot in the eccentric wheel. Wiegand's claim was that his design for the first time allowed such adjustments to be made regardless of whether the engine was operating in forward or reverse. In the image of the model the lever operating the steam inlet valve would rest upon the top of the eccentric which is the thin cylinder to the right center.
The patent model is constructed of brass and mounted on a hammered brass plate which is mounted on a wooden base. The brass base plate is inscribed “S. Lloyd Wiegand, Philadelphia, PA.” The control lever is shown at the left. The miniature hand crank at the right was intended to demonstrate the movement of the cut-off mechanism. 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.