From Engineering 125 years ago
EASTONS & ANDERSON POST OFFICE ENGINES
From Engineering 125 years ago
EASTONS & ANDERSON POST OFFICE ENGINES
THE MACHINERY AT THE NEW POST
OFFICE.
"THE machinery of the Post Office'' is a term which has
for so long a time been considered to refer to tbat gigantic
staff which constitutes one of the largest and most perfect
organisations connected with the public service, that it
is difficult to conceive of it as having any other application.
And possibly it might still have referred
only to the administrative and executive of this department,
but for the establishment of the postal telegraph
system, which has involved the adoption of some very
powerful machinery, A recent visit to the New Post Office
in St. Martin's-le-Grand, made by permission of Mr. Culley,
the engineer-in-chief to the department, brought under our
notice the most powerful, complete, and extensive appliances
for telegraphing in the world. So extensive, however, is
the machinery which aids in the working of the system, that
it will not be possible in a single article to do it justice.
We therefore prepose in the present notice to refer briefly
to the general arrangement of the pneumatic machinery,
and to describe in detail the source of motive power, the
engines and boilers, leaving the telegraphic apparatus for
description on a future occasion.
The new building has now become the centre of the telegraph
system of the United Kingdom, and the whole of the
basement and the upper floor, as well as a portion of the
first two floors, is occupied almost exclusively by the telegraphic
staff and machinery. A perfect network of wires
terminates in the building as a common focus, whilst no
less than thirty lines of subterranean tubes radiate from it
to various parts of London in connexion with the pneumatic
system of transmission, which forms an important part of
the telegraphic system. The machinery for working these
tubes consists of three compound air-compressing and exhausting
engines, each of 50 horse power, space having been
left in the engine-house for a fourth. These engines are supplied
with steam from four 50 horse power Cornish boilers.
The engine-house occupies one quadrangle or courtyard,
formed in the construction of the Post Office, and the boiler.
house another. Situated between these quadrangles, and
forming part of the main building, is the battery-room, a
spacious apartment 80ft. long by 70ft. wide. In this room
are the batteries, containing 30,000 cells, from which the
wires are carried in thick cable-like groups up a shaftway
to the telegraph room at the top of the building, whence
they radiate to their destinations. This room is composed
of three galleries resembling in plan the letter H,
and measuring 200 ft. in one direction, and 115 ft. in
the other. In this instrument room, which is well lighted
and ventilated, are placed the electrical instruments, and
the pneumatic transmitting apparatus. The battery of
pneumatic valves is connected with the engines in the basement
by two air mains, one for pressure, and the other for
exhaust. These mains are 18 in. by 9 in. flat pipes, which
are carried down the outside of the building in the quadrangle
in which the boiler-house is placed. At the bottom
they are continued under the battery room to the engines,
but there their form changes from square to round pipes of
cast iron, 18 in. in diameter. The reason for these pipes
having so large an area is that friction may be reduced, and
also that they may form containers, and so destroy the
pulsations caused by the strokes of the pumps. The transmitting
instruments are connected with thirty ranges of
2 1/4 in. and 3 in. lead pipes, which pass down a recess from
the instrument room to the basement, where they are carried
along the corridors upon two sets of wooden galleries suspended
from the ceiling by iron ties. These tubes pass
thence out to the streets, and diverge to various parts of
London. The transmitting instruments, which will form
the subject of a subsequent notice, are of vety simple, but
ingenious, construction. They are the invention of Mr.
Culley's assistant-engineer, Mr. J. W. Willmot, under
whose immediate superintendence the machinery at the New
Post Office was designed and fitted up.
Turning to the main subject of our present notice-the
air-compressing engines-we must refer to the two two-page
engravings published one with the present and the
other with our last week's number, these engravings representing
a side and an end elevation, and a plan, all in part
section. From these views it will be seen that the engines
-which have been constructed by the well-known firm
of Messrs. Eastons and Anderson-are beam engines of the
Wolff type, the high-pressure cylinder being 17 in. diameter,
with a 4 ft. 1 1/2 in. stroke, and the low-pressure cylinder
25 1/2. diameter with a 5 ft. 6 in. stroke; the cylinders
are not steam jacketted. The beams are each composed of
four wrought-iron plates placed as shown in the sections,
the main-centres, which are of wrought iron, being car-
ried on pedestals resting on entablatures, each supported
by six columns, resting on massive bed plates. These bedplates
are in their turn supported by heavy cast-iron frames
resting on lower bedplates, bedded on and secured to a
layer of concrete 6 ft. thick, which underlies the whole
building. The foundation bolts are 6 ft. long, with footlock
plates on their lower ends, and are let into holes 15 in.
in diameter formed in the concrete, and filled in with
Portland cement grout. This is no doubt a ready mode of
fix ing foundation bolts, but in the event of a bolt being
broken in screwing up-an accident which we have known
to happen on more than one occasion-it could only be replaced
with considerable difficulty. For this reason we
prefer a form of foundation in which the lower ends of the
bolts are accessible without disturbing the foundation
proper.
Upon the lower bedplate of each engine, and immediately
under the beam, are two exhausting and compressing pumps
each 35 in. diameter, and 3 ft. stroke, one of the pump rods
of each engine being coupled to the back links by the ordinary
parallel motion belonging to the piston rods, while for
the other rod a special parallel motion is provided. Each
pump is arranged either to draw through leather flap valves
from an 18 in. vacuum main laid between the pumps, or to
force through similar valves on the opposite side into two
15 in. pressure mains, which afterwards unite and form the
18 in. main already referred to. Each pump can be shut
off from either mains by screw slide valves, and by means
of similar valves air can be taken in from or discharged into
the atmosphere instead of from and into the vacuum and
pressure mains. The leather valves are 3 in. by 4 in., and
are arranged in groups of four; they have iron backing
pieces, and beat on gun-metal seats, so arranged that they
can be easily removed and replaced by others when out of
order. The arrangement of these valves is not one that we
can regard favourably, the top suction valves especially
being so placed that the current of air will interfere with
their prompt closing. The area through the valves also
appears to us much too small, and as a result of this we
should anticipate much noise in working. The air pumps
of which we have been speaking are intended to produce in
the mains a vacuum of 20 in. of mercury or a pressure
of 10 lb. per square inch, and it appears to us questionable
whether as such a pressure has to be worked against, it
would not have been better to have employed piston slides
instead of ordinary flap valves. At all events the experience
at our leading Bessemer works tends to prove
that these piston valves with a positive motion are the most
economical which can be used when the air has to be
pumped at a high pressure. Of course we are not forgetting
that the pressure required at Bessemer works is
more than twice as great as that necessary for the pneumatic
despatch ; but although for this reason the advantage
of the piston over the flap valves would not be so important
as in the latter instance, it would still be great.
Steam is used in the high-pressure cylinder at 70 lb.
pressure, and is distributed by double slides adjustable
by a right and left-handed screw, arranged so that the expansion
can be varied without stopping the engine. The
condensers are placed on the lower level nearly under the cylinders, and the trunk single-acting air pumps, 18 in. diameter,
2ft. stroke, are under the outer ends of the crankshafts,
and are worked by crank discs keyed on them. The
connexion with the condensers is formed by inclined pipes
8 in. diameter. We have ourselves an objection to plunger
air pumps on account of the facility they afford for air
leakage unless the packing is well looked after, a defect
from which the air pumps with submerged buckets are
free. The latter may really be run with the bucket packing in a very doubtful state without any great loss of efficiency.
The injection water is, in the engines we are describing,
taken from a tank under the battery room, supplied
either from a deep well, or from the water company's main.
The engines are fitted with centrifugal governors of the
Porter type, and they are also controlled by the difference
of pressure between the vacuum and pressure mains
acting through pistons working in small cylinders arranged
as shown in the longitudinal section. Both the governors
and pistons actuate rocking shafts by means of levers,
which, turning freely on the shafts, move them by stops so
as to close the throttle valves against weighted levers tending
to open them. Thus, if the speed or the pressure increases,
either regulator is free to act on the throttle valves.
It will be seen from our engraving that the floors, both of
the beam and engine room proper, are formed of cast-iron
plates of an open pattern, so as to allow of the diffusion of
as much light as possible. The access to the different level
is by iron staircases of similar design. It is to be regretted
that the necessity of not obstructing the light to
the windows of the buildings surrounding the quadrangle,
obliged the Office of Works to build an engine-house of
rather contracted and ungainly proportions, and which is,
in fact, unworthy of the machinery it contains.
The engines we have been describing are admirable pieces
of work, and no pains appears to have been spared by their
makers to render them a first-class job. Notwithstanding
this, however, we cannot regard them as fairly representing
modern blowing engine practice. The whole experience at
our leading iron works and Bessemer works is in favour of
vertical direct-acting engines, such, for instance, as the types
which have been so largely used in the Cleveland district.
Such engines take up less than half the floor area of the older
beam engines of equal power, while their first cost is materially
less, and their expense of maintenance very small.
The boilers which supply steam to the engines of which
we have been speaking, are placed in a house built in a
quadrangle corresponding with that occupied by the engine house, from which it is separated by the battery room. The
boilers are of the Cornish multi-tubular type, 6ft. 6 in. diameter,
and 20 ft. 2 in. long, each having two flues 2 ft. 6 in.
diameter, 14 ft. 6 in. long, and terminating in 74 3-in.
tubes 5 ft. 9 in. in length, and fitted with Vicars' self-feeding
furnaces, the hoppers of which are supplied with coal by
screw creepers from the coal store. The boiler flues communicate
with a lofty shaft which carries up the products
of combustion above the level of the roofs of the surrounding
buildings. In one corner of the quadrangle
is a well sunk into the chalk, this well terminating in an
Artesian boring. Two sets of three-throw pumps with
barrels 8 1/2 in. diameter, and 2 ft. stroke, will raise 210 gallons
per minute from this well. The pumps are worked by
three-throw cranks actuated through mortice spur gear by
either of two 14 horse power condensing beam engines, duplicates of each other, and each having a cylinder 14 in.
diameter, with 2 ft. 6 in. stroke. These engines are also
fitted with air-compressing pumps 12 in. diameter, 1 ft. 2 in.
stroke, which are intended to supply air to the machines
used for preparing the paper slips for the automatic transmitting
instruments whenever the main engines are not working.
Connected with each engine are three pumps, eaeh 4 in.
diameter, and 9 in. stroke. These pumps are used for feeding
the boilers, for circulating the warm water from the hot
wells into the passages of the main .building for warming
purposes, and for the high service cold water supply
required throughout the establishment. The flywheels
of these engines are turned up, and over them are belts,
which drive a main lay shaft, which transmits motion by
means of mortice mitre gear to an upright shaft. This
shaft in its turn actuates by a half-turn belt a shaft bung
to the ceiling of the corridor under the large operating room,
through the floor of which it transmits its motion to the tape
carriers employed to carry the message papers across the instrument room. From the main lay shaft a belt is carried to
a small room in the basement of the main building in which
are arranged a number of lathes for cutting up rolls of paper
into the discs which form the strips used in the recording
instruments. At the end of the shaft is a worm gearing into a
tangent wheel, which actuates a cross shaft running over
and in front of the boilers, and by means of eccentrics working
Vicars' furnaces. By means of pitched chains it also
actuates the 9-in. screw coal creeper which brings the fuel
from a coal store situated in the main building and accessible
from the street.
The two small engines are duplicates of each othter,
but ordinarily they will be employed doing different work.
Thus one engine will usually be employed to raise water
from the well into the tank from which all the engines draw
their injection, the speed of the engine thus employed being
regulated by a float which shuts off steam when the water
supply has risen to its proper level. The other engine
will, under these circumstances, drive the shafting and
the smaller pumps. These engines are intended to work at
a high rate of expansion, and are fitted with double slides,
so that in the event of one being disabled there will be power
enough by giving more steam in one engine to do the whole
work, while to provide for the independent working of the
boilers there is a donkey engine with feed pumps and rigger for driving the shaft actuating the stoking apparatus.
Before concluding, it may be interesting to notice the
rapidity and precision with which the transfer of the instruments
and staff from Telegraph-street to the New Post
Office was effected. It took place on the night of Saturday
the 17th of January last, under the superintendence of Mr.
H. Eaton, and upon that occasion a number of groups of
wires were successively disconnected from the instruments
at Telegraph-street and connected with those at St. Martin’s le
Grand. Every circuit was working to Telegraph-street
at 10 o'clock, but so perfect were all the arrangements and
so precisely had all the preliminary operations been carried
out that at five minutes past the hour they were all working
to the new building. A telegram in course of transmission
from Manchester was stopped en route, one half being delivered
in Telegraph-street and- the wires having been
shunted-the other half in St. Martin's-le-Grand. But a
few years since this transfer would have occupied several
days, but to such perfection have all the working details of
the telegraphic system been brought, that it was but the
work of a few minutes. The whole of the transfer was
effected without one mischance or hindrance, and reflects
great credit on the staff of the telegraphic department of the
Post Office.