The annexed engraving represents these valves as applied to a marine engine, aa is the steam cylinder, and b and c are two nozzles, either cast upon the cylinder, or firmly bolted to it; b is the steam nozzle, connected to the steam pipe by the neck d; and c is the eduction nozzle, communicating with the condenser by the neck or openingf; g g are the steam passages into the cylinder, and h h the eduction passages. In each nozzle are chambers to receive the cast-iron blocks mm and nn, which are ground to a perfectly plane surface on the face. The blocks m m have apertures, coinciding with the steam passages g g in the cylinder, and are firmly keyed against the cylinder by the keys o o; p p are the steam valves, which are flat plates of cast-iron; they are attached to the valve rods by a hinge joint, the object of which is to allow the valve to swing off the face of the valve seats or blocks mm, to allow any water to escape which may find its way into the cylinder. The rods by which the valves are moved are connected, so as to cause the valves to move together. The blocks n n have apertures corresponding to the passages in the eduction nozzle, against which they are firmly keyed by the keys qq.
The eduction valves r r are flat plates of cast-iron, similar to the steam valves: but as they are never required to leave the valve seat, they are fastened to the valve rod without a hinge-joint. Upon examination of the above arrangement, it will be seen that the steam valves are pressed to their seats by the steam in the steam nozzle, and the eduction valves are pressed against their seats by the steam in the cylinder. The lever by which the steam valves are moved is connected by a rod to that which works the eduction valves, so that the one set counterbalances the other.