IN QUESTIONS AND ANSWERS For Machinists, Firemen, Electricians and Steam Engineers
(Page 2 of 7)
Q. Now, if your rocker-arm stood at a quarter,
and your eccentric out of plumb, how would you take the measure for
A. Simply bring them plumb and take the measure;
that is the only right way.
Q. After you have measured the rods, what would
A. They should be put on and the valve set.
Q. What do you move or do first, to set a valve
after connections are made?
A. Move the eccentric in the direction the engine
is to run, until the valve begins to take steam or lead, then
tighten the eccentric temporarily with set screws, then move the
crank-pin over to the other dead center, and see how much lead it
has; if equal the valve is set.
Q. What is meant by the lead of valve?
A. The opening the valve has when the piston is
at the beginning of its stroke.
Q. What lead should large engine have?
A. About 1/16 of an inch.
High speed engines must have a quick opening or good lead.
Q. Now if you find the valve laps out ? of an
inch on one end, and the proper lead on the other, what would you
A. Divide the difference, by moving the valve
one-half it is out, by adjusting the valve-gear.
Q. How much?
A. The valve has 1/16 of an
inch lead at one end and laps ? of an inch at the other end; the
valve is out 7/16 of an inch; then the valve
must be adjusted by the nuts one-half it is out, making
7/32 of an inch. then throw the crank on the
other dead center, move the eccentric whichever way will bring you
back to 1/16 of an inch lead, then tighten
temporarily with set screws, throw crank over the other dead
center, and the valve will be set. After valve is set, tighten the
eccentric for good.
Q. But if it is not set, what would you
A. Go through the same performance until it is
set. Some valve-rods have a yoke that slips over the valve, while
the adjusting and jam-nuts are between the stuffing box and the
rocker-arm pin. When a valve-rod has no nuts, the adjusting must be
done at the eccentric rod. To lengthen or shorten the stroke of
valve-rod, raise or lower the eccentric-rod pin in the slot, at the
bottom of the rocker-arm, whichever way suits the
Q. Now, after you have set your valve, keyed
everything up properly, and there was a thud or dead sound in the
engine or cylinder, what would you do, or where would you look for
A. In the exhaust being choked. The steam chest
cover must be taken off, then uncouple the valve, turn the valve up
sideways and move it until the steam edge has the proper lead with
the steam-port, then place a square on the valve-seat of the
cylinder, and against the valve-face, to see how the exhaust lead
on the opposite steam-port corresponds; if it is choked, then
scribe it by allowing a little over double the steam lead.
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