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effort. The M. & L. booster is also termed a
tender tractor truck and is designed to replace
one of the tender trucks, utilizing the weight of
the tender for additional adhesion and tractive
effort. This employs a two cylinder double acting
steam engine geared to one axle and connected
through cranks and side rods to the second axle.
The M. & L. booster is, of course, intended for
application to existing equipment. Its use
requires fitting the locomotive with the necessary
piping and valves for the control. The throttle
valve is mounted as a by pass on the main steam
pipe and is controlled by an air line from the
cab. The steam line is carried to the tender
truck through the necessary flexible connections.
The truck itself can be directly applied to the
tender in place of any standard type.
The operation of the booster will be apparent
from the illustrations showing its construction.
Live steam is admitted to the main steam line
through the throttle valve controlled from the
cab. Pressure in this line operates the piston on
the auxiliary cylinder and throws the idler gear
in mesh with the axle gear. Steam is then
admitted to the cylinders and the booster develops
power at a speed synchronized with the engine
speed through the adhesion of the truck wheels
to the rail. When the booster throttle valve is
closed the idler gear automatically pulls out of
mesh and the steam engine comes to rest. The
gearing is so arranged that the booster can be
thrown in with the locomotive at rest or in motion.
Actual tests have shown that the booster engine
will develop 250 H. P. at a speed of seven miles
per hour. This corresponds to an increased
tractive effort of 13.500 lbs. Assuming that the
locomotive can supply steam up to a speed of
fifteen miles per hour, the horsepower developed
would then be about 500 and the additional
tractive effort 27.000 lbs. From these figures the
possibility of increasing the tonnage rating on
the medium classes of freight locomotives is
obvious. The rated tractive effort on such
equipment varies from 35.000 lbs. to 60.000 lbs.
In developing the design of this booster one
of the principal problems was the main journals
of the truck. These were designed to carry the
largest weight of tender at present contemplated,
namely a 15.000 gallon tank, which has a journal
load of 28.000 lbs. In addition, with the booster
developing its maximum power, there is a
reaction from the side rods of approximately the
same amount, giving a resultant maximum load
of 39.500 lbs. It was accordingly determined to
use the self-aligning roller bearing mounted as
shown in the accompanying drawings.
The journal box construction is somewhat
unusual, being intended to meet the peculiar
conditions of the application. The cranks and
side rods mounted outboard of the journals
require a split type of box to allow of inspection
of the bearing without removal of the cranks.
The box must, in addition, serve as a driving
member for the truck. In the design determined
upon, the lower half of the box is merely an oil
cellar for retaining the lubricant.
At the present time the principal field of
usefulness of the booster is in freight service. It
allows an increase in the tonnage rating of
locomotives primarily through increasing the
tractive effort on ruling grades. The advantage in
starting is largely one of reduced upkeep on
equipment, since the increased draw bar pull for
starting, eliminates much of the strain on draft
gears through taking slack. Although the
locomotive booster is of comparatively recent origin,
the soundness of the principle involved has been
definitely established, and the future
development will be largely one of refinement in
mechanical detail.
H. E. Bninner.
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