SETTING THE VALVES OF THE DUPLEX PUMP.
The following rule applies to nearly all duplex pumps of the Worthington type. The valves are usually of the common “D” valve type, working on the cylinder iron, or bronze seats, and suitably “set.” Sufficient cushion at the end of each stroke is provided by separate valves in the ports.
Rule.—1, Locate the steam piston in the center of the cylinder, [Fig. 305]. This is accomplished by pushing the piston to one end of its stroke against the cylinder head and marking the rod with a scriber at the face of the stuffing-box, and then bringing the piston in contact with the opposite head; 2, divide exactly the length of this contact stroke. Shove the piston back to this half mark, which brings the piston directly in the center of the steam cylinder, F; 3, perform the same operation with the other side; 4, place the slide valves, which have no lap, to cover all the ports, E; 5, pass the valve stem through the stuffing-box and gland. The operation of placing the pistons in the center of their cylinders will bring the levers and rock shafts in a vertical position; 6, screw the valve stem through the nuts until the hole in the eye of the valve stem head comes in a line with the hole in the links, connecting the rocker shaft; then put the pins in their places; 7, adjust the nuts on both sides of the lugs of the valves to leave about 1⁄4″ or 1⁄8″ loss motion on each side.
This process of adjustment being performed with both cylinders, the steam valves are set. In short the travel of the two valves is simply equalized.