Steven’s Patent Model of a Steam Engine Cut-off Valve – ca 1861

Description:

This model was filed with the application to the U.S. Patent Office for Patent Number 33,855 issued to Francis B. Stevens of Weehawken, New Jersey on December 3, 1861. The patent was for an improved design for the mechanism controlling the inlet valve of a steam engine. It was based on the previous Patent Number 1,950 of January 25, 1841 by himself and Robert L. Stevens.

Both patents 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.

The images of the model show it to be a frame holding the four vertical lift rods for the valves of a steam engine. A hand crank at the left of the model operates an eccentric wheel which is connected by rods to a rock shaft at the other end of the frame. Four tappets are mounted on the rockshaft, each operating a valve. The exhaust valves are operated directly by the tappets on the shaft. A hollow rock shaft sliding on the first is operated by a second eccentric and is used to vary the cut-off of the inlet valves. The tappets for the inlet valves have hinged faces which can be adjusted up or down by a small lever. The amount of this movement adjusts the point at which steam is cut off.

Stevens’ valve gear designs were widely used in steamships driven by beam engines. The first use was on the steamship Albany which served on the Hudson River. The vessel was owned by Robert L. Stevens, the uncle of Francis.

The patent model is constructed of brass and steel. The top of the frame holding the tappets is engraved “F. B. Stevens.” All of the key elements of the patent are illustrated by the model. The image of the tappet end of the model shows the four tappets and lift rods. The steam inlet valve rods are the first and third from the left. The hinged face of the steam inlet tappet can be seen in the image of the side of the model. A full description of the operation of the valve gear along with complete diagrams of the patent can be found in the patent document online at the United States Patent and Trademark Office website, www.uspto.gov.