_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.