Calvin F. (Calvin Franklin) Swingle.

Cyclopedia of locomotive engineering, with examination questions and answers; a practical manual on the construction, care and management of modern locomotives, including boiler construction, valves and valve gears, indicators, locomotive equipments, including headlights and mechanical stokers. Spec online

. (page 8 of 42)
Online LibraryCalvin F. (Calvin Franklin) SwingleCyclopedia of locomotive engineering, with examination questions and answers; a practical manual on the construction, care and management of modern locomotives, including boiler construction, valves and valve gears, indicators, locomotive equipments, including headlights and mechanical stokers. Spec → online text (page 8 of 42)
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^hen it comes exactly under the other point of the
tram, stop. The engine is now on the right forward
dead center, and a vertical line should be scribed oh
the guides exactly in line with the front end of the
crosshead. This line indicates the extreme forward^
travel of the crosshead, and it ;s important that it
should be placed there.

While the engine is in the position it now is, that is,
on the right forward dead center, and the valve geir
in the backward motion with all the lost motion taken
up in that direction, take the valve tram and from
point C, Fig. 62, scribe an arc on the valve rod, start-
ing slightly above the parallel line and extending con-
siderably below it The distance of this arc, measured
on the parallel line from center F, indicates the posi-
tion of the valve, as regards lap or lead for backward
motion. The reason this arc is drawn below the line
is that the back-up eccentric is moving the valve, and
by having the arc below the parallel line it is Easily
distinguished from the other arc soon to be scribed for
the forward motion. Now pinch the wheels back until
the crankpin is about 6 in. above the dead center.
Then put the reverse lever in full forward motion and
pinch ahead until the pin is again on the forward dead
center, and with the valve tram again set in point C
scribe another arc on the valve rod, this time extend- *
ing above the parallel line. The distance this arc is
ahead or back of the point F indicates the amount of
lap or lead the valve has in the forward motion, when
the crankpin h at right forward dead center^^^Qj^



14a



LOCOMOTIVE ENGINEERING



Before making any adjustments, go round to the
left side of the engine and find the left forward dead
center; also mark the left valve rod for both forward
and back motion in the same manner as the right valve
rod was marked. Having completed the location of
the forward dead centers for both sides, the next move
is to start on the right-hand side again, and pinch the
engine towards the right back dead center, which is to



f



RIGHT HAND






±



r



Q



^>^



-/^



m



n



^^



LEFT HAND



F, |^ ,



}



FiauBB 67



be found in the same manner as the forward one was.
Next find the left back dead center, marking the valve
stems and crossheads in both instances exactly as
before.

The valve rods will now show a marking similar to
that illustrated by Fig. 67, with the exception that Inc
figures may not coincide, as the figures shown in Fig
67 are merely assumed for purposes of explanation.
As before stated, the arcs which have Jbeeny scribed

yitizedbyLiOOgle



VALVE SETTING I4j

across the parallel lines indicate by their position
relative to the port marks F and B whether the valve
has lap or lead at either dead center. If an arc comes
between the port marks it indicates lap, if outside it
indicates lead. Referring to Fig. 67, the two forward
motion arcs on the right side valve rod, which are
distinguished from the back motion marks by being
above the parallel line, show that the valve has J^-in.
lead at the forward port mark and t^-in. lap at the
back port mark.

When the valve tram reaches from center C to either
center B or center F, it indicates that the valve is at
the point of cut-off, and since the valve is to travel
eqilal distances each way from these points, it follows
that by measuring the distance from B or F to the
arcs, it may be determined how much and whether to
lengthen or shorten the eccentric blades. First take
the right forward motion. The distance from F to
the mark above the line is % in., and from B to the
mark for back motion is -fp in., therefore the length of
the right forward motion ^eccentric blade must be
changed so as to equalize these distances, and the
point to be determined is, shall it be lengthened o**
shortened? This can be done in the following man*
ner: Take a small pair of dividers and find the exact
center between the two tram marks above the parallel
line. If this center is ahead of center C the eccentric
blade must be shortened, if back of it the blade must
be lengthened. If the engine has a direct valve
motion, this rule is to be reversed and the adjustments
made accordingly.

The next point to be determined is, how much shall
the blade be lengthened or shortened? A good rule
to follow in this instance is this: When the arcs on

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144 1-OCOMOTIVE ENGINEERING

the valve rod are both back < \ both ahead of the port
marks F and B, the lengtU of the e^ccentric blade
should be altered an amount equal to one-half the sum
of the distances between the port ma^ ks and the arcs,
or if one arc is back and the other is ahead of their
respective port marks, the length of the blade should
be changed an amount equal to one half the difference
of the distances between the port marks and the arcs.
In this particular case the valve has traveled too far
back, as shown by the J^-in. lead on the forward port
mark and the tV-ih. lap on t^e back port mark.
Therefore the blade must be shortened one-half the sum

of these distances, or ^ — ^^-^-^ ^ In. This will square

the valve for right forward motion, or in other words
equalize its travel in either direction from mid posi-
tion, as may be proved by the following simple calcu-
lation. The valve had J^-in. lead at the forward port
mark, the eccentric blade is shortened ^V ii^-t thus
bringing the point of the tram that much nearer to F.
Then J^-A = /yi'^-» which is now the lead at the
forward end. At the back end, instead of lead, the
valve had ^V i^^- 1<^P»

After the blade is shortened VV ^'^^ ^ will be found
that the valve has been moved that distance ahead
from its former position. Then by deducting the -^^
in. lap from ]^ in. change it will be found that the
valve has ^y in. lead at the back end also. It may be
assumed that the valves are to have ^ in. lead when in
full gear, and as the valve under consideration now has
/^ in. at both ends, it will be necessary tq reduce it by
turning the eccentric back upon the shaft. However,
no changes should be made until all the tram marks
on both sides of the engine have been examined and a



VALVE SETTING 14$

memorandum made of the changes required, as, for
'nstance, R. F« Ecc, shorten blade ^^ in., -^^ in. lead
off.

The tram marks for the right backward motion
should be examined next. These marks are below
the parallel line, and measurements' show that the
valve has -^ in. lead at the forward end and )i in. lap
at the back; therefore the blade of the right back up

eccentric must be shortened thus, - — ^^» ^f in.

This will square the valve for right backward motion,
but it will still have ^-in. lap at both ends, when ^f-in.
lead is required; therefore the eccentric must be
turned ahead. These changes should be noted down
as follows: R. B. Ecc, shorten blade ^^ in., -^-in.
lead on.

If the upper and lower rocker arms are of the same
length the figures for changing the length of the eccen-
tric blades will be all right, but if, as is often the
case, the lower arm is shorter than the upper one, the
length of the blades will not need to be changed quite
as much as is indicated by the marks on the valve rod.
But it will be assumed in this instance that the arms
are of equal length, and the lengths of the eccentric
blades for the right-hand side may be adjusted accord-
ing to the above figures.

Next go to the left-hand side. By reference to Fig.
67 it will be seen that the valve has -^j-in. lap on the
left forward motion in front and ^y-in. lap behind. In
this instance the valve has not traveled far enough
back, therefore the blade must be lengthened one-
half the difference between these distances or ^ ^ «*

2

^ in. This will equalize the lap at both ends, makinf



&4.6



LOCOMOTIVE ENGINEERING



it now r\ in., and in order to obtain the ^ipin. lead
desired it will be necessary to move the eccentric ahead
on the snaft an amount sufficient to overcome the
^in. lap plus ^in. lead, a total of ^ in. This is to
be noted down as follows: L. F. Ecc., lengthen blade
A in., ^-ia. lead on.

Examination of the two left back motion marks
shows that the valve has fi-in. lead at the back and



.Q



r



LEFT HAND



F M B.



■^^



,.^



?



RIGHT HAND



f




.B M f:



i



■^p-^



Figure 68



^-in. lead in front. Therefore the back up eccentric

This will



8 1. 1

jlade should be lengthened = \\ ia



give the valve W-va. lead at both ends, but as ^V"^^*
lead is all that is required, it will be necessary to turn
the eccentric back on the shaft far enough to over-
come W in. of this surplus lead. Note this down
also as follows: L. B. Ecc, lengthen blade \\ in., ^

^«ad off. Digitized by Google



VALVE SETTING 147

The lengths of all the eccentric blades should now
be adjusted according to the figures obtained, after
which it will be in order to set the eccentrics. It is
generally best to set the forward motion eccentric first,-
because it is easier to get at than the back motion one
is; then if the backward motion eccentric needs to be
changed enough to affect the lead in forward motion,
the forward motion eccentric can easily be reset, and
it will need to be moved so little [that the backward
motion will not be affected enough to require any
further attention.

As before stated, it is desired to give the valve
i^^in. lead in full gear in both forward and backward
motion, and before setting the eccentrics it will be
necessary to have lead marks on the valve rods for a
guide. To get these marks, set a pair of dividers to
the distance between the centers B and F, Fig. 68, plus
the lead, in this instance i>^ in. +^» iH ^^' Then
with one point of the dividers in center F scribe an arc
£ across the parallel line, back of center B, also from
center B scribe an arc D in front of F. These points,
E and D, will serve as guides in setting the eccentrics
for lead. The next move is to place the engine on
the dead center; either one will do, but for conven-
ience it may be assumed that it is the right forward
dead center. When adjusting the lengths of the
eccentric blades it was found that with the engine and
reverse lever in this position the valve had /y"!*^- 1^^^-
This must be reduced to -^g in., and it might be done
by simply turning the right forward motion eccentric
back upon the driving shaft, but that would take up
the lost motion in the opposite direction to what it is
when the engine is running ahead, and this would
cause an error in the working of the valve.y The

• Digitized by VjOOQ IC



t48 LOCOMOTIVE ENGINEERING

proper method is to turn the eccentric backward far
enough to take off all the lead, and then turn it slowly
^ahead until the valve tram will reach from center G,
«Mg. 62, to the lead mark D, Fig. 68. Next throw the
lever into full back gear and proceed to set the right
backward motion eccentric.

After getting the right backward motion eccentric
blade adjusted to the correct length it was found that
the valve had ^-in. lap at both ends; therefore this
eccentric ^should be slowly turned ahead on the Shaft
until -the tram will reach from center C to lead mark
1E/ Fig. 68. This will square the right-hand valve
and give it the desired lead, and the next move is. to
go around to the left side, throw the reverse lever into
full gear ahead again and pinch the engine onto left
forward center.

After adjusting the left forward eccentric blade to
the correct length it was found that the valve had
T^j-in. lap. The eccentric must therefore be turned
ahead until the tram will reach from center C on the
left cylinder to lead mark D on the left valve rod.
Next proceed to set the left backward motion eccen-
tric, and in doing this the wheels should be pinched
ahead about 6 in., then place the reverse lever in full
back gear and pinch the engine back onto the center.
This is done to take up all the lost motion in the direc-
tion in which the engine is to run — a very important
matter that should never be lost sight of in working
from the dead center for either forward or backward
motion. After getting the left backward motion
eccentric blade the right length the valve had ^f -in.
lead at both ends of the stroke. The eccentric should
therefore be turned back sufficiently far to take off all
*he lead. Then with all the lost motion taken up, turn



VALVE SETTING 149

the eccentric slowly ahead until the tram point will
drop into lead mark E, Fig. 68.

The engine is now square, and the valves have the
correct amount of lead all around. The eccentrics
should be securely fastened in their proper location
either by set screws or keys, and it will be next in
order to ascertain the points of cut-off, so that they
may be equalized as near as possible, for be it remem-
bered that no matter how accurate the valves may have
been set, as regards lead, travel, etc., they very seldom
cut off the steam at the same distance from the com-
mencement of the stroke at each end of the cylinder,
and one cylinder may be getting more steam than the
other. This is due to the fact that the link motion is
not a perfect valve gear, various errors being intro-
duced by the angularity of the main rod, and eccentric
rods, and the off-set of the link pin holes from the
link arc, but these errors can be almost entirely elimi-
nated by making certain changes, among which may
be mentioned the off-setting of the link saddle stud,
although with case-hardened links and the saddle
rigidly bolted to the link this method is not always
practicable.

Another very common method is to equalize the for-
ward motion by changing the length of the backward
motion eccentric blades, thus sacrificing equality of
lead and cut-off in the back gear, but as a locomotive
does the greater portion of its work in the forward
gear, except* it be a switch engine, this plan is per-
missible.

Another method employed to some extent is to
sacrifice equality of lead in both forward and back gear
for equality of cut-off. But before either plan can be
adopted it will first be necessary to find the points of



ISO LOCOMOTIVE ENGINEERING

cut-o£f as the valves are now set. As a locomotive
engine performs the principal part of its work with
the reverse lever hooked back towards the center notch
and the valves cutting off at early points in the stroke,
it is more important that the steam should be equally
distributed with the lever in the working notch than
with It down in the corner.

Passenger engines usually cut-off at from 4 to 6 in.,
and, freight engines at from 6 to 9 in. As in setting
the eccentrics, a start at finding the points of cut-off
may be made with the engine on either dead center,
but for convenience it may be assumed in this instance
that the engine has been placed on the right forward
dead center. First try the cut-off in backward motion.
Pinch the wheels backward until the crosshead has
traveled about 6 in. from the extreme travel mark on
the front end of the guides. Then stop the motion,
and with the point of the valve tram in center C, Fig.
62, move the reverse lever back of the center until the
tram will drop into the forward port mark F. Put the
lever one notch farther back, then pinch the wheels
backward until the tram again drops into the forward
port mark F, thus indicating that the point of cut-oft
has been reached. Now measure the distance froiri
the front travel mark to t)ie front end of the crosj
head. Suppose it is found to be 7J4 in. Chalk thij
down on the front end of the outside guide. Use th^
outside guide for the backward motion, because the
backward motion eccentric is on the outside. Now
pinch the wheels farther back until the steam is cut off
on left side back end of cylinder, which can be ascer-
tained by the use of the tram in the same manner as
on the right side. It may be assumed that cut-off
takes place when the piston has traveled Sji in. from



VALVE SETTING 151

beginning of stroke. Now turn the wheels still farther
back, until the right pin passes the front center and
reaches the point where cut-off takes place, which
will be assumed to be 8 in. from commencement of
stroke. These figures should all be marked down with
chalk on the outside guides for the backward motion
as they are found, and the reverse lever must be left in
the same notch until all four points of cut-off for back-
ward motion are located. Next pinch the engine still
farther back until the left pin passes the front center
and cut-off for this end is reached, which may be taken
at 9 in. for the present.

These investigations show that cut-off for the right
cylinder occurs at 754 in. of the backward and 8 in. of
the forward stroke, and that for the left cylinder cut-
off takes place at 9 in. of the backward and 8^ in. of
the forward stroke. These figures indicate that the
right-hand valve is traveling a little too far ahead and
the left valve a short distance too far back, and the
cut-off for each side may be equalized by slightly
changing*the lengths of the backward motion eccen-
tric blades; that of the right-hand one must be length-
ened and the left one will need to be shortened, and
how much to change them may be found as follows:

Taking the left side first, cut-off occurs on the front
end of cylinder at 9 in. and on the back end at 8^

in., and the average is — — -= Sji in., which is the

2

distance from each end of the stroke at which cut-off

will occur when it is equalized. Now pinch the wheels

forward enough to bring the crosshead 8^ in. from

the end of the stroke and enough 'more to take up all

the lost motion when turning back. Next pinch the

engine backward until the crosshead is again S]4 i^



IJ2 LOCOMOTIVE ENGINEERING

from the beginning of the stroke at the front end, and
with the valve tram in center C, Fig. 62, scribe a mark
on the valve rod. This mark will be a short distance
ahead of center F, and this distance shows how much too
far back the valve is traveling, and the eccentric blade
must be shortened enough to throw the valve ahead
that much. This will equalize the cut-off for the left
side in the backward motion, and the right side should
be treated in the same manner, except that in this case
the backward motion eccentric blade must be length-
ened, because the valve was traveling too far ahead,
the cut-off for the forward stroke being 8 in. and for
the backward stroke 7>i in., and the average is

Zzl= 7^ in., which will be the point of cut-off for

the right side in backward motion when the proper
change is made.

This will leave considerable difference between the
two sides, the cut-off on the left side occurring at Sji
in. and on the right side at 7J^ in., but this will be
remedied later on, and the next move will be to equal-
ize the cut-off for the forward motion by commencing
with the backward stroke on the right-hand side.
Pinch the engine ahead until the pin passes the for-
ward center and draws the crosshead back 6j4 in. from
the beginning of the stroke. Move the reverse lever
ahead to the corner, then move it slowly backward
until the valve closes the port, as will be indicated by
the valve tram when it reaches from center C to center
F, Fig. 62; then put the lever in the first notch ahead
of that position and leave it there until the points of
cut-off have all beffen found for the four strokes. Now
pinch the engine ahead until the tram again shows that
the point of cut-off is reached. This may^be assumed to



VALVE SETTING 153

be 8 in. back of beginning of the stroke. Mark this

down on the front end of right inside guide, then turn

the wheels ahead and get the cut-off for the front end

of left-hand cylinder, which will be, say 7 in. Again

pinching ahead, find the cut-off for the back end of

the right-hand side to be 8^ in., and still turning

ahead, find cut-off for back end of left side to take

place at 8 in.

For convenience, the cut-off for the left side may be

equalized first. It was found that cut-off occurred at 7

in. for the backward stroke and at 8 in. for the forward

7 + 8
stroke, the average being '- = 7^ in., and in order

to equalize the travel of the valve, which now
travels too far ahead, it will be necessary to lengthen
the eccentric blade. Pinch the wheels back far enough
to bring the crosshead within less than 7J^ in. of the
end of the stroke, so that when turned ahead again all
lost motion may be overcome. Now pinch ahead
again until the crosshead is exactly 7J^ in. from the
beginning of the stroke, and with the valve stem tram
in center C scribe a mark on the valve rod, and the
distance of this mark from center B is the amount
that the eccentric blade must be lengthened. This
will equalize the cut-off for forward motion on the left
side, and the right sidie ne:fet demands attention. Here
the point of cut-off for the backward stroke was 8 in.,
and for forward stroke 8^ in., the average , being

o I 03/

—=8^ in., which is the point at which cut-ofi

for forward motion on the right side must be equalized
for the present.

The right forward motion eccentric blade will also
need to be lengthened, as the valve travel^ too far

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154 LOCOMOTIVE ENGINEERING

ahead, and the correct amount to lengthen the blade
may be found in the same manner as with the left
side. This will leave the points of cut-off for forward
motion as follows: for, right-hand side, 8^ in.; left
side, jyi in. In backward motion, as equalized, cut-
off for right side is 7^ in., left side 8^ in. It will
thus be seen that in forward gear cut-off is earliest on
left side and in back gear it occurs latest on that side.
In order to overcome this unequal condition one of
two things may be done, either lengthen the link
hanger on the left side or shorten hanger on the right
side. The former method will be adopted, but before
making any alterations it will be necessary to ascertain
the amount to lengthen, and this may be done in the
following manner:

Put the reverse lever in the same notch that it was
in when the cut-off in forward gear was found, and
measure the distance from any stationary point directly
above or below the upper link hanger pin on the left
side to the center of that pin. Now pinch the engine
ahead far enough to bring the left crosshead the same
distance from the beginning of the stroke as the right
crosshead was when cut-off took place, which distance
is 8^ in. This is where cut-off must occur on the left
side also. Now move the reverse lever ahead about
four notches, and then with the point of the valve
tram in center C move the lever slowly back until cut-
off occurs as indicated by the tram. Now measure the
distance again, from the same stationary point to the
center of the upper hanger pin. The difference
between this distance and the distance between these
two points as first found is the amount the left hanger
must be lengthened to equalize the cut-off on both
^ides, or raising the tumbling shaft box slightly more

Digitized by VjOOQl€



VALVE SETTING 155

than this on the right-hand side would bring about the
same/esult as shortening the link hanger on that side.
This change will slightly affect the operation of the
valves in back gear, for this reason: The nearer the
link block is to the center of the link, the shorter will
be the cut-off, and the change made, viz., lengthening
the banger, while it throws the block farther below
the center of the link in forward gear, thus delaying
the cut-off, at the same time brings the link block
nearer the center of the link in back gear, thus acceler-
ating the cut-off, and this is the result wished for to
cause the two sides to cut off nearer equal in back
gear, as it will be remembered that cut-off on the left
side occurred at 8^ in. in the back gear and y% in. on
the right side in back gear. The amount that the
hanger has been lengthened may not exactly equalize
the cut-off in back gear, but it will bring it near enough
for all practical purposes, for the reason that the
engine does very little work in back gear. Owing to
the space occupied by the piston rod in the back end
of the cylinder, the cut-off should occur J^or ^ in. later
in the back end than in the front end of the cylinder if
it is desired that the same volume of steam be admitted
to each end of the cylinder.

The next points to be determined relate exclusively
to the exhaust opening and closure with reference to
release and compression. These events, as has been
already explained, are controlled by inside clearance



Online LibraryCalvin F. (Calvin Franklin) SwingleCyclopedia of locomotive engineering, with examination questions and answers; a practical manual on the construction, care and management of modern locomotives, including boiler construction, valves and valve gears, indicators, locomotive equipments, including headlights and mechanical stokers. Spec → online text (page 8 of 42)