Improvements in connection with Cranks for Compound Steam Engines.
Year: 1889

page_text: Date of Application, 15th Nov., 1889
Complete Specification Left, 3rd Sept., 1890-Accepted, 1st Nov., 189C
PROVISIONAL SPECIFICATION.
Improvements in connection with Cranks for Compound Steam
Engines.
I ANDREW LECKIE of Cambridge Terrace West Hartlepool in the County of
Durham Engineer do hereby declare the nature of this invention to be as follows:-
This invention relates to compound triple cylinder steam engines in which the
pistons are connected to separate cranks on one and the same shaft and has for its
object to so construct and arrange the cranks that latent strain is prevented or reduced
to a minimum and an almost steady flow of steam from the boiler or boilers is attained
whereby priming is reduced or entirely prevented and also undue tear and wear of the
slide valves or piston valves cylinders pistons piston rods and packing rings and the
breakage of springs.
According to this invention with reference to compound engines employing two
high pressure cylinders the cranks of these cylinders are arranged on the crank shaft
at right angles to each other so that the admission of steam from the boilers to the
high pressure cylinders takes place at four equal intervals in each revolution of the
crank shaft instead of twice as is the case with ordinary compound and triple expansion
engines thereby admitting of the steam valves on the boilers and throttle valves being
opened out to increase the initial pressure in those two cylinders.
To further equalize the speed at all parts of the rotations of the crank shaft and to
reduce the latent twisting strain the cranks of the low pressure cylinder are counter-
weighted so as to counteract the accelerated velocity caused by the excess in weight of
the low pressure piston beyond the combined weight of the others the balance weight
being made about equal to the combined weight of the crank, crank pin, lower half
of connecting rod and its bushes.
The low pressure cylinder cranks are arranged on the crank shaft equidistant
circumferentially between the cranks of the two high pressure cylinders and when
these cranks are also balanced as before described the latent strain on the crank shaft
is reduced to a minimum the side strain is prevented and the vertical strain is
considerably diminished and consequently the durability of the engine is considerably
increased.
When built" crank shafts are used for the high pressure cylinders instead of the
ordinary solid forged cranks the additional weight of the head of the crank produces
a latent twisting strain upon the shafts (and coupling bolts when so fitted) between
each set of cranks thereby causing a side strain on the journal bushes causing great
side wear and also the slackening of bushes transversely and consequent knocking.
To prevent these defects I employ cranks ballanced in the forging as before described
thus preventing the shafts from getting out of line and heating and the breakage of
sole plates and the loosening of connections by vibrations.
1000
COMPLETE SPECIFICATION.
Improvements in connection with Cranks for Compound Steam
Engines.
I ANDREW LEOKIE of Cambridge Terrace West Hartlepool in the County of
Durham Engineer do hereby declare the nature of this invention and in what
manner the same is to be performed to be particularly described and ascertained in
and by the following statement:-
This invention relates to compound steam engines having two bigh pressure

page_text: cylinders and a single low pressure cylinder the pistons of which are connected to
separate cranks on one and the same shaft and has for its object to so construct and
arrange the cranks that twisting strain is reduced to a minimum and an almost steady
flow of steam from the boiler or boilers is attained whereby priming is reduced or
entirely prevented as also is undue wear and tear of the slide valves or piston valves,
cylinders, pistons, piston rods and packing rings and the breakage of springs.
In order that my invention may be clearly understood I shall now proceed to
describe the same with reference to the accompanying drawing wherein
Figure 1 represents diagrammatically a plan of a compound engine with cranks
arranged according to this invention.
Figure 2 being a side elevation of the crank shaft and
Figure 3 a corresponding end view thereof similar letters of reference indicating
corresponding parts in the several figures.
A A are the two high pressure cylinders and B is the low pressure cylinder. The
cranks A² of the high pressure cylinders are arranged on the crank shaft at right
angles to each other or nearly so in order that the admission of steam from the boilers
to the high pressure cylinders may take place at four equal or nearly equidistant
intervals in each revolution of the crank shaft 1) (instead of twice as is the case with
ordinary compound and triple expansion engines) thereby admitting of the steam
valves on the boilers and throttle valves being fully opened out to increase the initial
pressure in these two cylinders.
To further equalize the speed at all parts of the rotations of the crank shaft and to
reduce the twisting strain the one or both of the crank cheeks of the low pressure
cylinder is or are cast or forged with counterweights as shewn at B³ so as to counteract
the accelerating force caused by the excess in weight of the low pressure piston with
rods, bushes and cranks &c. beyond the combined weights of the others.
The low pressure cylinder crank cheeks are arranged on the crank shaft as at B²
equi-distant circumferentially between the cranks of the two high pressure cylinders
and when these crank cheeks are also balanced as before described the twisting strain
on the crank shaft is reduced to a minimum the side strain or pendulous-strain is
prevented and the vertical strain is considerably diminished and consequently the
durability of the engine is much increased.
When "built" crank shafts without counterbalances are used for the high pressure
cylinders instead of the ordinary solid forged cranks, the weight of the cranks produce
an increase of the twisting and oscillating strain upon the shafts (and coupling bolts
when so fitted) between each set of cranks thereby increasing the side strain in the
journal bushes causing greater side wear and also the slackening of bushes transversely
and consequent "knocking." To prevent these defects I employ cranks balanced
in the forging as-before described these balanced weights I prefer to be about the
weight of the lower half of connecting rod with bushes crank pins and cranks-which-
will prevent the shafts from getting out of line and heating and a whole train of
breakages all being the result of continued excessive vibration but when balanced the
engines may be safely increased in speed.
In Figures 2 and 3 I have shewn only the low pressure cylinder crank cheeks
balanced but in Figures 4 and I have shewn all the crank cheeks so balanced.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed I declaro that what I
claim is.-
1st. In compound steam engines having two high pressure cylinders and a single
low pressure cylinder the arrangement of three separate cranks upon a single crank
shaft the two high pressure cranks being at right angles or nearly so and the low
pressure crank making an equal angle with each of the high pressure cranks and
being placed on that side of the crank shaft which is opposite to them substantially as
hereinbefore described.
2nd. In compound steam engines balancing the low pressure cranks or the high
pressure cranks or both the high and low pressure cranks by means of counterweights

page_text: cast or forged in one piece with the crank cheeks substantially as and for the purposes
berein before described.
3rd. The relative arrangement and countor weighting of the cranks of compound
steam engines substantially as and for the purposes herein before described.
Dated this 30th day of August 1890.
ANDREW LECKIE.