The valve motion (see [Figs. 302], [303]) of one cylinder is communicated or produced by the piston of the other through the medium of rocker arms and links. By means of the small lost motion of the levers the pistons have a slight pause at the end of each stroke, which allows the water valves to seat quietly, thus preventing any slam or jar.
With this arrangement, as one of the steam valves must always be open, there can be no dead point, thus removing the liability of the pump to stick. The simplicity of the duplex movement is at once evident, each valve is dependent upon its counter part, and both directly control the action of the steam, which is supplied through one simple throttle valve.
Note.—Of the effect produced by the steam-moved direct-acting pump of much greater capacity it may be said there are now in use pumps of this class, exerting over 250 horse-power, delivering five million gallons of water in twenty-four hours through main pipes, say thirty inches diameter and fourteen miles long, without the use of an air chamber, and which do their work so quietly, steadily, and gently, that a nickel coin set on edge on the extreme end of the pump would not be overthrown by any jar or motion of the pump while it was doing this work.
Fig. 302.
Fig. 303.
The adoption of the Worthington design of duplex pumps, has been well nigh universal, especially so since the expiration of the earlier patents. Nearly all leading manufacturers now make “duplex pumps.” Single, compound and triple expansion.