The valve A is fitted upon its seat in the steam-chest B, and moved to and fro over the ports in the usual manner. The back of the valve is a plane surface, parallel with its face. Along the sides of the steam-chest I provide two parallel guides--one, _b_, inclined downward and outward, and the other, _b¹_, inclined upward and outward, as shown in Fig. 1, from a point in the same plane with the back of the valve and at an angle considerably greater than the angle of repose of the metal. Theoretically, the plate should move down its inclined supports if the angle of inclination exceeds at all the angle of repose; but practically, under conditions, often unfavorable, existing in the steam-chest to render the action certain, this angle should be largely in excess, as shown in the model and drawings. In the instance shown I have provided chambers G at the ends of the steam-chest, through which the steam may pass over the ends of the pressure-plate to the ports; but any other approved passage for the steam may be provided. The pressure-plate C fits snugly in the steam-chest lengthwise, and moves freely in it crosswise. This plate has an opening in the top and a hollow center, so that the steam entering at the top passes through the center and into the chambers G, at the ends of the steam-chest. The bottom of this plate has a plane surface, parallel with the back of the valve A, and beyond this plane surface it has lateral inclines _c c¹_, parallel with the lateral inclines _b b¹_ on the sides of the steam-chest, so that when the plate is in place its lateral inclines rest upon and fit closely to the inclines on the chest, thus supporting the plane surface of the bottom of the plate close to the top of the valve. The width of the plate being less than that of the chest B, it will be seen that the plate in this position would have a certain range of movement upon the inclines crosswise of the steam-chest. A screw-stop, H, passes through the steam-chest, and bears upon the adjacent side of the pressure-plate, which will still be free to be moved crosswise of the valve. The operation is as follows: The stop H being adjusted to the point at which it is desired to maintain the pressure-plate, the pressure of the steam will act upon the plate and tend to force it down the inclines _b b¹_ crosswise of the valve and against the stop, which will thus determine the range of movement of the plate and the relation between its plane surface and the back of the valve. At the same time the stop, being entirely independent of or disconnected from the plate, can be readjusted as required to compensate for any wear upon the surfaces of the valve or its seat, and the steam will at all times maintain the plate at the point determined by the adjustment of the stop. This adjustment is, of course, made without opening the steam-chest.