From Engineering 125 years ago




"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


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.