IMPROVEMENTS IN TRAMWAY LOCOMOTIVES, AND IN BOILERS FOR THE SAME
Year: 1874

page_text: PROVISIONAL SPECIFICATION left by Leonard Jennett Todd at the
Office of the Commissioners of Patents, with his Petition, on the
17th January 1874.
I, LEONARD JENNETT TODD, of Leith, in the County of Mid Lothian,
North Britain, Engineer, do hereby declare the nature of the said
Invention for "IMPROVEMENTS IN TRAMWAY LOCOMOTIVES, AND IN BOILERS FOR
THE SAME," to be as follows, that is to say :-
This Invention has principally for its object the arranging of the
driving platform and brake gear of locomotives and cars for tramways
in an improved and superior manner, and the proportioning of boilers
for the same, so that they can be much more safely worked than is at
present the case when only a single attendant is employed to both drive
the car and also attend to the boiler.
The driving platform I place right in front of the engine, and I
arrange the driving handles and parts thus:-The driver's seat occupies
the centre, and on the left side by preference I place the regulator, hand
brake, and sand handles, and also a frame containing the pressure gauge

page_text: and two glass gauges. On the right of the seat by preference I place
the reversing power brake and sand handles; and in the front by
preference I place an air whistle, handle blown by the blast or a small
special fan, and from the roof of the cab I allow the steam whistle
handle to hang; and to the guard plate in front I attach two large 5
brush holders for cleaning rails.
Underneath the driving platform I place the brake shaft, with one arm
extending below and coupled to the power brake cylinder, which I
prefer to fix to the top of the front plate. The other arm then extends
below the hand brake, and is connected so that it can rise freely when 1
the power brake is in use. Brake rods communicate with the driving
wheel brake shoes, and another rod passes below the engine and projects
behind, where it is coupled to the ordinary car brake gear, simply by a
rod or chain, which the rigid car couplings allow.
Each driving wheel brake rod and each cross brake bar of the cars I 1
fit with a spring, by preference consisting of one or more rubber rings
to equalise the strain on each of the blocks when the brakes are hard up,
all of which for a street railway makes a very simple and efficient
continuous brake gear. This brake gear, and also the arrangement of
the driving platform gear just described, are applicable to all classes of 2
tramway locomotives, whether propelled by steam or other power.
In geared locomotives which have the crank and main axles placed in
a nearly vertical plane I regulate the distance between these centres in
an improved manner, by which the proper working depth of the toothed
wheels can be more easily adjusted and maintained than at present.
In one case I place a wedge with set screws, either above the main
bearing or below the crank shaft; or in another I use a horizontal lever
and screw below the crank shaft to effect this adjustment.
I work the coupling pin of the locomotive in an improved manner,
and more conveniently than at present by fitting it with a cross handle,
to be worked from either one or both sides of the engine.
The last part of my Invention consists in proportioning the parts of
tramway locomotive boilers in an improved and superior manner, so that
they can be used with much greater safety than at present in cases
where no special fireman is employed, and where one man has to both
drive the locomotive and also attend to the boiler. As street cars usually

page_text: only cary about 40 passengers each, it would hardly pay to use steam
power, if that necessarily involved the employment of a special fireman
to attend to the boiler, as then there would be three attendants for each
car, namely, a fireman, a driver, and a conductor, instead of the two
attendants now used with horses; yet it would be a very risky matter
with an ordinary locomotive boiler to dispense with a fireman on a
tramway, and to trust entirely to the driver to both carefully drive his
car amongst a crowd of other vehicles, and also to attend to the boiler,
especially when (as is the case with all horizontal vertical locomotive
boilers) the fluctuations of pressure and water level take place very
rapidly; for as many boiler explosions take place annually from the
neglect of stokers, in situations where the stoker has only to do the one
single thing of attending to his boiler, and where that boiler only slowly
fluctuates in pressure and water level, a steam car can hardly escape
accident for long if these fluctuations take place very rapidly, and if
there is no special stoker at all. Such cars may and indeed have been
safely run during a single journey, or even during many journeys, con-
ducted under specially favorable circumstances, but for the ordinary
day and especially night work of a tramway they are simply dangerous
and unfitted. Nor for such work is it safe to trust to any device for
self-acting fuel and water feeds, for such contrivances are not altogether
reliable, even in the largest stationary boilers, and would be very much
less so in portable ones of the smallest proportions, and so it is simply
dangerous to use any class of cither horizontal or vertical locomotivo
boilers as at present made in street cars which have not also a special
fireman to attend to them.
Now as far as safety is concerned, the amount of attention that a
boiler requires varies inversely according to the amount of water it
contains, and to the area of its water level per square foot of grate
surface. Suppose a boiler has 1 cubic foot of water capacity, and 1
square foot of water area per foot of grate, and that it varies in pressure
and water level a certain amount in five minutes, then it is quite
evident that if we give 5 feet of water capacity and 5 feet of water area
(the grate area remaining the same), these variations will take 5
times as long as before, for the given size of grate can only develope a
given amount of heat in a given time, and as it is now surrounded by
5 times as much water as before it follows that this water will now be 5
times as long as before in rising to a given temperature or pressure, and

page_text: again that it will be 5 times as long as before in falling from any given
temperature, as there is now 5 times as much heat stored in it; and so
also is it with the water level, which will then take 5 times as long as
before to vary to a given extent.
An ordinary horizontal locomotive boiler contains about 5 cubic feet
of water and 3 square feet of water area, and a vertical boiler about 4
cubic feet of water, and 1.5 square feet of water area per foot of grate,
and they do not require attention oftener than nor indeed so often as
every 10 minutes.
Now my improved method of proportioning may be shown thus:-
In one case I make a boiler with, say, 5 times as much water capacity
and 5 times as much water area as at present, say, with 25 cubic feet of
water capacity, and 15 square feet of water level area per foot of grate,
and also with a very deep furnace, and this improved boiler then as far
as safety is concerned only requires attention every 40 or 50 minutes,
instead of every 10 minutes as before, and as a street car does not usually
require longer than half an hour to make a run, it follows that if its
boiler is thus proportioned it can then with perfect safety be left to
itself during that time, or in other words, I proportion my improved
street car boiler thus :-I fix in it a low water line the ordinary height
above the furnace crown plate, and then between this and the highest
water level I allow as many cubic feet of water capacity as will not be
less than the entire evaporation required for the journey, so that if the
boiler is full of water at starting it is almost impossible that danger can
arise from lowness of water while running, for although not a drop of
water is pumped into the boiler while at work, yet during the out journey
of, say, 3 miles, or half an hour's work, the water will only have gone
down half way towards the low water line, and should the driver even
then show the almost incredible neglect of starting back on the return
journey without looking to the boiler or pumping during the journey,
yet still at the end of the double run of 6 miles or one hour's work the
water will only then have descended to the low water level, and the
boiler will still be as safe as an ordinary boiler.
It must be understood that different roads and sizes of cars will alter
the figures here given.
It of course will be a matter of convenience to always keep the feed
pump partly on while running, and so not to let the water always run

page_text: working of the pump is not of the very slightest consequence as regards
safety, for the boiler provided it is full at starting cannot boil empty
during the journey, and it will be the duty of the inspecting engineer
to see that the rule of always starting with full water is most rigidly
enforced.
The boiler is also quite safe from any sudden rise of pressure, as the
small grate cannot give off sufficient heat both to drive the car and also
to dangerously heat the great amount of water surrounding it, except
during a long period of time.
Now a car boiler designed with this specially large water capacity and
water area may be properly called an accumulator boiler, because it goes
on for a long time receiving heat from its small furnace and storing it
up in its water, and yet only slightly raising the pressure, and again
during a long period it gives off heat from its store, and yet only very
slowly reduces its pressure or water level. It is true that all boilers are
subject to this action, but at present in only such a small degree as to be
useless for the purpose herein mentioned, namely, of enabling a special
fireman to be dispensed with. Just as in an ordinary water pumping
engine there is always somewhat of the accumulator action taking place
from the water entering into and receeding from the air bell and pipes,
yet still such an engine is not said to possess an accumulator unless
there is a very large and special provision made for some capacious
yielding part into which the surplus water can enter and be stored under
pressure until required; so also all steam boilers possess somewhat of
the accumulator action, as they in a small measure are constantly either
storing up heat in or giving out heat from their contained water, yet
still it is only when a street car boiler is made with such specially large
water proportions, as herein-before described, that it constitutes a proper
accumulator boiler.
All locomotive boilers, whether horizontal or vertical, have such a
very small heat reservoir (in the contained water) that with very little
provocation they so quickly vary in pressure and water level that they
must always have a special fireman to attend to them to regulate there
sudden fluctuations; but by my improved system of proportioning I
make the heat reservoir (in the contained water) so great that even with
the greatest provocation these fluctuations of pressure and water level

page_text: can only take place so very slowly, that for the short journeys of a street
railway the boiler can with perfect safety be left to itself while the
locomotive is running, and thus by my improved system of proportioning
street car boilers I gain two important elements of utility which present
car boilers do not possess, first, that the boiler is very much safer than at|
present, and second, that a special fireman is not required.
My improved street car boiler consists merely of the same parts as
other boilers, and my improvement consists therefore in proportioning
and arranging these parts in a special manner which is widely different
from any existing practice, and which no person would adopt in a street
car or even approach unless he is influenced by the considerations which
I have already given, and which although very simple when now stated
have yet cost me much time and labor to thus simply put into practice.
Unless influenced by my conclusions no person will even approach near
to my improved proportions of parts, as they necessarily make a boiler
much heavier and more expensive than one of the ordinary proportions.
It is heavier because of its great amount of water and of its enlarged
shell, which must be thicker than a smaller one. Ordinarily the designer
tries to make a street car boiler as light as possible to keep down the
total weight and power required (which is right supposing there is a
special fireman to do nothing else but attend to this very small boiler,
but not otherwise), and he will thus rather work away from my improved
proportion than towards it, unless he begins to meditate and act on my
carefully arrived at conclusion, which is this, that the very simplest and
safest plan of making a street car boiler which shall not require attention
while ruuning is to make it with a water capacity above the low water
line which shall not be less than the total evaporation required for an
entire run, and to make the furnace of such a capacity that it will hold
fuel for an entire run.
Now on attempting to work out the design of an accumulator car
boiler it will be found that it necessarily entails very considerable
differences from existing practice, and as an example I proportion a
vertical accumulator car boiler thus:-It is 42 inches diameter and 84
inches high; furnace 18 inches diameter, and placed close to one side of
shell for the sake of the fire-hole; it is 24 inches deep from top of bars
to fire-hole. There is a water grate to prevent clinkers, which would
otherwise be a great inconvenience in such a narrow deep furnace. The
combustion chamber is 36 inches diameter, and concentric with the main

page_text: shell; the top of it is 33 inches from top of boiler. Where the furnace
is clear I fit it with water tubes open at both ends, and above furnace
with hanging water tubes. The low water level I fix 7 inches above the
tube plate, and the high water level 10 inches from top of boiler, and
between these levels there are 12 cubic fect of water capacity, which at
50 pounds of water per indicated horse-power per hour equals 15 horses
power for an hour, or 30 horses power for half an hour. Such proportions
will answer for an ordinary car, but of course the proportions can bo
varied, provided that the water capacity between the highest and lowest
levels is made not less than the total evaporation required for the whole
journey, or for an entire run from one end of the line to the other, or
from one terminus to the other between which the car runs.