The improvements which constitute the advantages of this throttle valve will be appreciated from the following description, reference being had to the illustrations, of which Fig. 1 is a perspective view. Fig. 2 a vertical section across the axis, and Fig. 3 a section parallel with the axis. A is a spherical chamber, containing the valve, B. It is divided by the partition, C C, into the compartments, D and E, one for th^ r admission of steam into the valve, and the other for the passage of steam from the valve ports to the steam-chest. The latter is annular, and surrounds the valve, as seen at E, Fig. 3. The valve is in the form of a hollow frustum, being supported on the axis, F, by four arms or partitions, 6, which also serve to strengthen against any unequal pressure that it may receive. The valve seat consists of a shell surrounding the valve, and fitting it closely. It is joined to the partition, C, at one extremity, and to the case. A, at the other. In it are four recesses or passages, d d, extending from the chamber, D, and uniting in a single chamber, H, at the end of the valve. The valve stem or spindle is packed and supported in the usual manner, having an adjusting screw at each end, e e, to regulate its pressure on the seat; and I is the lever for connecting it with the governor. The valve has four oblong ports or openings at its sides, f f; and there are corresponding openings in the seat, g ^, between the recesses, d d. The steam enters from the boiler into chamber, D, filling the interior of the valve, and also the passages, and chamber, H. As the ports are opened, it passes into the annular passage, E, surrounding the valve seat, and thence to the steam chest. The course of the steam, both in its passage through the valve and through the surrounding chamber, is indicated by arrows. The adjoining surfaces of the valve and seat are grooved, so as to constitute a steam-tight joint, and the adjustment of steam in and upon the valve is such as to reduce friction to a minimum rate, and thus produce what may be called a balanced valve. The pressure of the steam on a considerable portion of the exterior surface of the valve, by means of the passages and chamber, d andH, tends to overcome friction, and makes it sensitive in a high degree, while the interior arrangement is such that the force of the steam in escaping by one port, is counterbalanced by the same force in the opposite positions of the four different ports. The supporting partitions, 6, receive the back pressure of the steam and throw it upon the center, and form in fact four equal and distinct passages for the steam to the ports. The considerable area of the four ports and their united action produce an extreme degree of sensibility and a very slight turn of the valve varies the opening greatly. So rapid and perfect is its operation that it is difficult to detect a difference in its revolution, when suddenly changing from light to heavy labor of the engine, o^n^mce versa. It was patented April 13, 1858, by the inventor, T. S. La France, of Elmira N. Y., who will furnish any further information upon being addressed as La France & Colman, of the same place.
This article was originally published with the title "La France's Improved Throttle Valve" in Scientific American 13, 41, 324 (June 1858)