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. DUPLEX OIL PUMPS. The pattern of pump shown in Fig. 306, is especially designed for use in connection with hydraulic lifts and cranes, cotton presses, testing machines, hydraulic riveting and punching machines, and hydraulic presses of all kinds. Also for _oil pipe lines_ (see Table, page 341), mining purposes, and such services as require the delivery of liquids under heavy pressures. There are four single acting outside packed plungers, which work into the ends of the water cylinders, the latter having central partitions; each individual valve has its own cover or bonnet. The arrangement of compound steam cylinders is shown. The water valves are easily accessible, and are contained in small chambers, capable of resisting very heavy pressures. The general arrangement shown in the engraving is subject to numerous alterations, according to various requirements, _but the general characteristic of four outside packed plungers is in all cases preserved_. [Illustration: FIG. 306.] SPECIAL DUPLEX PUMP. (_Outside packed Plunger Pattern for High Pressure._) TABLE.