The Bennington evening banner. (Bennington, Vt.) 19??-1961, 1915-04-15
ENGINES
Speed of Fast Locomotives and
How III Is Attained.
BIG WHEELS A NECESSITY.
But Equally Important Are the Steam
Valves, the Grstss In tho Firebox and
the Ability to Make Steam Rapidly.
Other Vital Factors.

the Ability to Make Steam Rapidly.
Other Vital Factors.
The average person thinks that the
bigger the locomotive and the greater
the diameter OF It's driving wheels tho
faster it. will go. and in the popular
mind these are the only reasons one
engine can run faster" than another.
The loeoli3o sc, although one of the
simplest and iest known of machines,
embodies nrHmi,us devices not visible
TO the eyo OF the casual observer
which are most vital clements in its
efficiency and speed For example.
much OF the power of the big express
'n2ine depends r~on tn" '".eam valves
md the CRATES IN . l.'e,ox Quite as
much rs it does upon the mere big
ness Of the driving wheels. Al the
same time it is true that large wheels
IN ordinary fast running are II con
vencnce and in the very highest
speeds necessity. II becomes ncces
sary, OF course. to tighten the load as
the wheels are enlarged and increase
the speed, which introduces the sec
ond phase Of the problem-thc si+ires
and heating surface
Fast engines, to continue their work
for long time at a stretch, must
make steam very rapidly. To accom-
pish this the heat of the fire must
come in contact with the water at n
great many points. a large firebox
involves Il CRATE of large area to admit
air to the iire-a difficult matter since
but Il small distance separates the
wheels. the width OF the fireboy being
thus limited, while the length must
come within the limit TO which the
fireman can throw his coal
A third factor is the counterbalance.
the solid filing fixed between the
spokes of the driving wheels opposite
the connecting rods This is TO balance
the weight of the cranks. parallel rods
and connections and. in addition. the
force on the wheels o; the weight
of the moving piston in the cylinder.
Lacking this balance the wheels would
roll too rapidly when the rods and con
nections were moving downward and
too slowly when they were moving up
ward, thus causing ierky motion.
However, as the influence OF the
weight is varied by the centrifugal
force, which. In turn. is greater or less
according as the speed is high or low,
it happens that a counterweight which
is suitable at Il speed or forty or fifty
miles an hour produces an injurious
pound" on the rails at scventy-1vc
miles an hour.
1t follows, therefore, that the weight
must be heavier than the rods and con-
nections because Il part of its Office Is
to balance the piston and other parts
that slide horizontally and are unin-
fluenced by centrifugal force. AS the
speed increases the downward motion
of the weight. as that part OF the
wheel rolls over to the front, makes
The wheel with its load press down
upon the rail with so much more force
ing upward on the other side that the
effect upon the rail Is rs If Il heavy
blow were delivered upon it with
hammer.
So to use an engine successfully at
the highest speed it is necessary to
make the countcrweight lighter than
would be correct for moderate speeds.
The light weights are not necessarily
at the lower speed, but their
use would cause unnecessary wear and
lear OF the engine and the track and
In some cases would even cause I'M
pleasant jerks upon the passenger
cars. For this reason fast engines are
seldom built unless the% can be used
In fast service all the time.
Properly proportioned valve open
.ugs are absolutely essential to fast
engine These admit the steam to the
opposite ends Of the cylinder alter
nately, as the connecting rod moves
first forward and then backward, and
in a fast engine they must admit
large volume of steam very quickly.
The valves must be moved so as first
10 o1en one passage and close the 9th
er and then as rapidly as possible close
the first and open the second.
1t will be noticed by even the most
casual observer that the opening TO
ct the steam out of the cylinders into
the smokestaek is several times as
argc us that for admitting the "live'
steam. But even with this 1t requires
| considerable amount OF power to
rorce the steam out with sufficient
thickness. This must be done in the
traction of n second
There are many engines that can get
steam into the cylinders quickly |
enough and that are otherwise all
light for high speed, but which are
not so arranged 10 get rid of this
steam which has been used and is
,nly in the way. 1t is this rapid ex-
oulsion of the dead" steam that makes !
he vigorous puf's at the top of the |
that seem to indicate that |
he locomotive Is doing tremendous |
lmont Of work. 1t should be remem. |
,ered however, that this noise is not |
he result of real work, but only OF |
his after operation. which engine
builders would avoid. There is class
II locomotives. those arranged on the !
compound system, in which the puts
ire so faint that the engine would
.ppln fn bu loino pntbipr az Ill ~