MISCELLANEOUS APPLICATIONS OF PNEUMATIC CONVEYING
=Pneumatic Despatch Tubes.= The ordinary pneumatic conveyor picks
up material at one point and unloads it at another and continues
this course consistently, whereas the “pneumatic despatch tube” is
a conveyor of small articles enclosed in a special cartridge which
is built to fit the tube and which travels to and fro as required,
carrying a variety of articles, or if necessary, the same articles,
backwards and forwards between the same two stations or a series of
fixed stations.
The despatch tube thus constitutes an effective “mechanical messenger.”
One or more tubes are run between the points to be connected, with a
despatch and receiving terminal at each end, or if necessary, a single
line to operate in both directions can be designed. The tubes vary from
1½ ins. to 4 ins. diameter, and they are also made of oval sections up
to 4 ins. × 7 ins.; rectangular tubes have been installed in special
installations, chiefly in telephone exchanges for convenience in
dealing with certain cards there employed.
=Tubes.= The tubes are of lead and are usually encased for protection
against mechanical damage, and the erection is carried out with great
care so as to preserve the smooth interior. Joints occur at intervals
of 28 ft. or less, and are “wiped” with an ordinary plumber’s joint
over an internal mandril which is heated previous to insertion in the
tube. Air-tight joints and smooth interiors are absolutely essential to
a successful installation.
=Carriers.= The carriers or cartridges in which the material to be
transmitted is placed are made of gutta-percha covered at the ends with
felt. One end of the container is closed and the other end is left
open, but a “skirt” of felt surrounds the open end, and, as this is the
“trailing” end and the air pressure is behind it, the air forces open
the “skirt,” making a tight fit and preventing leakage of air past the
carrier. The nose of the carrier is usually fitted with a felt “buffer”
which also assists in making an air-tight fit. A carrier for a 2½ in.
tube is 6¾ ins. long and weighs empty about 3 ozs. Fig. 26 shows a
large carrier.
=Methods of Working.= Pneumatic tubes are worked either by air above
atmospheric pressure or by reducing the pressure below atmospheric. In
the pressure system the usual pressure is about 10 lbs. per sq. in.
above atmospheric pressure, whilst in the suction system the vacuum
employed is equivalent to about 6½ lbs. per sq. in.
[Illustration: FIG. 26.—TYPICAL LAMSON INTERCOMMUNICATION CARRIER.]
Also, the method of working may be either “continuous” or
“intermittent”; in the first system the air, either above or below
atmospheric pressure, is circulating continuously and the cartridge
or carrier is inserted into a stream of air already in circulation,
whilst in the “intermittent” system the power, either pressure or
suction, is admitted to the conveyor tube only after the carrier has
been inserted, and it is again cut off when the carrier reaches the end
of its journey.
To a great extent the success of a pneumatic tube system is the speed
at which it can transmit the message sent by this means. In the
“continuous” system, working above atmospheric pressure, the speed is
not so great as in the “intermittent” scheme, because the pressure in
the tube is the same in front of and behind the carrier, which has
to displace the air in front of it. In the “intermittent” system the
pressure is turned on after the carrier is in place, and the advancing
carrier has only to move the air at atmospheric pressure. On the other
hand, if suction is employed, the “intermittent” system is slower
than the “continuous” system because the air has to be exhausted to a
certain point before the carrier begins to travel. It is true that it
will begin to move as soon as the difference in pressure amounts to a
few ounces, but there is a distinct “time lag” compared with inserting
the cartridge into a tube continuously exhausted when it starts off at
practically full pressure and speed immediately.
The difference in time is stated by Kemp to be 3 per cent. longer with
“continuous” pressure, compared with “intermittent” pressure at 6 lbs.
per sq. in.; the difference increasing to 6 per cent. when the pressure
is raised to 14 lbs. per sq. in. The average working speed of these
tubes is from 25 to 30 miles per hour.
=Power Required for Operation.= It is difficult to determine the actual
amount of power necessary to carry a cartridge through a tube. _Kemp’s
Engineer’s Year Book_ states that, working at the standard pressure
of 10 lbs. per sq. in., the power required is theoretically 3·35 h.p.
for a 2½ in. tube, 1 mile long, but actual experience suggests that at
least 50 per cent. should be added to allow for losses from various
causes, making the actual power, say, 5 h.p. per 2½ in. tube per mile.
Pressure receivers or tanks are inserted between the pump and the
travelling tube to compensate for the impulses due to the irregularity
of the pumps and also to act as reservoirs furnishing additional power
during periods of abnormal working.
The vacuum system takes less power (for a definite time of
transmission) than is required by the pressure method of working,
but local conditions always influence results considerably, and it
is inadvisable to give any definite figure as to the power required,
without actual knowledge of the system and conditions involved.
The air compressors are usually driven electrically, but they can, of
course, be operated by any other prime mover such as oil, gas, or steam
engines. It is economical to combine the pressure and suction systems
by arranging the air compressor to draw air from the vacuum receiver
into the compressor cylinders whence it is returned to the pressure
line.
Automatic valves keep the pressures in the pressure and vacuum sides
of the system within pre-determined limits. “Make up” air is admitted
by the automatic opening of an atmospheric valve when the pressure
side of the system is low and the vacuum side high, so that the pump
is deprived of sufficient air to operate the system efficiently.
Should the conditions become reversed, that is, a low vacuum and a
high pressure, then the pump is working against a high back pressure,
and this is reduced by the opening of an atmospheric relief valve
which remains open until the vacuum is restored to normal pressure.
This system is preferable to and more economical than the use of two
separate pumping and exhausting machines.
Elaborate and valuable tables of horse-power required by compressors
and of “transit times” for distances up to 4,500 yds. with 1½ in., 2¼
in., and 3 in. tubes are given in _Kemp’s Engineer’s Year Book_.
The Lamson Tube Co., Ltd., have brought what was originally invented as
a means of conveying persons to a practical business accessory, capable
of saving a great amount of time by despatching sketches, papers, small
articles, money, etc., here, there, and everywhere at the rate of 30
miles an hour.
The utility of these plants has long been recognised by banking
establishments, the General Post Office, large stores, factories,
newspaper publishing offices, etc. (see Figs. 27 and 28).
In addition to the conveyance of messages and papers, they are
frequently installed to convey money and bills from the numerous
departments of a large store to the cashiers, thus saving time and
effecting economy in labour and floor space. One cashier can attend to
from 10 to 15 stations, or in small establishments all the stations can
be centralized around the book-keeper.
The installation of a power-driven plant is not essential, providing
that the service required is not too great. A foot power pneumatic
service is available and it is in use in many business establishments.
In this system the methods of transportation are similar to those in
a power plant, but the tubes are brought to a special cabinet 15 ins.
square by 2 ft. 6 ins. high, in which is mounted a foot-operated pump
of patented design without bellows or cords. The pump is operated
as and when the service is required, and there is no loss of any
description when the apparatus is not in use.
=Pneumatic Tubes for Heavy Articles.= It is interesting to recall,
especially in view of the proposed use of pneumatically-propelled
parcel-conveying trains by the G.P.O. in London, the proposal made by
Mr. Medhurst, in 1810, when it was suggested that a carriage somewhat
similar to the modern railway carriage should be moved through a
tunnel by pneumatic means. So long ago as 1667, Denin Papin read before
the Royal Society a paper entitled “A Double Pneumatic Pump,” and
definite mention of despatch tubes was made in this paper.
[Illustration: FIG. 27.—TUBE CENTRAL IN WHOLESALE DRUG HOUSE,
DISTRIBUTING ORDERS TO ALL DEPARTMENTS.]
[Illustration: FIG. 28.—LAMSON DISTRIBUTING STATION IN WELL-KNOWN
PUBLISHING HOUSE.]
In 1840 a pneumatic railway was actually built and worked between
London and Croydon, and in view of its success was followed by others
between Dalkey and Kingstown and between Exeter and Plymouth. From this
it will be seen that transportation by pneumatic means is not modern in
its application, and was originally intended for very large tubes and
weights, but modern development has been toward small tubes and light
weights.
=The Vacuum Cleaner.= The pneumatic transporting of material in the
form of dust has been brought to a very high state of perfection during
recent years and an enormous number of plants is now in use, ranging
from the hand-propelled machine to very large stationary equipments.
Certain hand-propelled machines have been constructed in such a way
that the fan is directly operated by gearing from the running wheels,
and after a few moments a very considerable speed is attained and the
suction of the fan is used for lifting the dust from the surface over
which the apparatus is travelling.
Numerous designs of more powerful machines actuated by hand bellows
have been placed on the market and these possess the advantage that
they are independent of the use of power; but it is not altogether easy
to operate a machine by one hand and to manipulate the nozzle with the
other.
Electrically driven machines of almost numberless designs are
available. These usually employ a high speed fan of the single-stage
type, but a piston pump is embodied in some designs.
In the removal of dust the same principle applies as in the conveying
of heavier materials, i.e. it is not so imperative to obtain a high
vacuum as it is to have a large volume of air moving at high velocity,
hence the multi-stage turbine machine has distinct advantages as
regards weight of material moved and economy of power.
The multi-stage exhauster consists of turbine wheels mounted on a
single shaft, the air being drawn into the first wheel, from this
to the second wheel and so on right through the machine, each wheel
increasing the suction on the intake end according to the total number
of wheels or stages. This style of machine is procurable in either the
stationary or portable type, and in both it is made in various sizes,
the portable machines ranging from 1/12 h.p. up to ½ h.p. for domestic
purposes, and from 1½ to 3 h.p. on trucks for cleaning electrical
machinery, railway carriages, etc. Figs. 29 and 30 illustrate typical
stationary and portable plants respectively.
[Illustration: FIG. 29.—STATIONARY TURBO-EXHAUSTER WITH DUST SEPARATOR.]
[Illustration: FIG. 30.—PORTABLE TURBO-EXHAUSTER DRIVEN BY 1½ H.P. D.C.
MOTOR.]
It is not generally recognized what enormous amounts of dust and dirt
may be extracted by these machines. From one London hotel a ½ h.p.
cleaner removed 166 lbs. of dust from the carpets of the public
rooms only. On a cleaning test in a first class dining car on one of
the English railways 25 lbs. of dust was removed from 38 sq. yds. of
carpet. A rug in front of a lift in a London stores yielded 91 lbs. 1
oz. of dirt to a small machine.
The stationary plants are usually installed in the basements of large
office buildings, theatres, hotels, clubs, etc., and the whole building
is piped suitably, wall plugs or connectors being fitted to which the
staff make connection by flexible hose as and when required. The free
end of the flexible hose is fitted with one or other of a series of
special nozzles, the latter being adapted to the varying requirements
of everything in the room from floor to ceiling.
With the portable hand sets or even with the larger truck type,
the design is complete as a working unit; the equipment is used as
manufactured and there is little or no chance for the user to endanger
the working efficiency of the plant. In permanent plants, however, as
installed in hotels, etc., it is necessary that all points previously
mentioned regarding pipe lines, valves, junctions, bends, etc., should
be considered and acted upon.
The pipe lines should be too large rather than restricted in any
way, the suction flexible should be kept as short as possible, and
if necessary extra connections should be allowed rather than require
flexibles too long for use without “kinking.”
[Illustration: FIG. 31.—SUCTION CLEANING FOR RAILWAY CARRIAGE CUSHIONS.]
[Illustration: FIG. 32.—STURTEVANT EQUIPMENT FOR OFFICE CLEANING.]
Fig. 31 illustrates a stationary suction cleaning plant applied to
cleaning railway carriage cushions, and Fig. 32 shows a similar
installation in use in an office building.
=Cleaning by Air Blast.= By transferring the hose from the suction
side to the discharge, a suction cleaner may be used to blow dust from
machinery of all kinds and from places that are high up and cannot be
cleaned economically by suction. For cleaning electric generators and
motors by blast, these machines have many advantages, and on account of
the large volume of air handled they are much to be preferred to the
small-volume high pressure jet of the ordinary air compressor often
used for this purpose. With the portable turbo-blower there is no
danger of damage to the insulation through high pressure, or through
the carrying of moisture and oil into the windings with the air jet.
=Pumping by Compressed Air.= Although, generally speaking, the
raising of water by compressed air is not an economical method, it is
frequently adopted in mining and tunnelling where the use of steam or
electricity is objectionable. In these cases, cost of operation is a
minor factor, and it may be interesting to give a few particulars of
this form of pneumatic conveying.
The simplest form of compressed air pump consists of a closed chamber
or tank immersed in the water, to be raised or fixed at such a level
that the water will flow into the tank. An air pipe is connected to
the top of the chamber, and the rising main is carried inside the tank
to the bottom. On opening the air valve, pressure is exerted on the
surface of the water in the tank, and the water is expelled through the
lift pipe or rising main. On closing the air valve, water again fills
up the tank, and the process is repeated.
A decided improvement on this pump is the return air pump, which
consists of two closed chambers connected through valves with the
rising main. The compressed air pipe passes through a two-way valve,
either into one tank or the other, this valve being positively
operated. The method of working is similar to that of the single acting
pump, considering each chamber separately, but one tank is filling
while the other is being emptied.
The air expelled from the filling tank, instead of being discharged
to atmosphere, and part of its expansive power lost, is carried back
through the pipe, which would be the air intake pipe when discharging,
through a port in the two-way valve, and into the compressor intake
pipe. The air leaving the filling tank is naturally above atmospheric
pressure, and assists the piston on entering the compressor, thus
reducing the power absorbed in driving the latter.
=Air-lift Pumping.= The air-lift pump is a common means of conveying by
pneumatic means and should not be confused with the above methods of
raising water by compressed air.
In the air-lift method of pumping air under pressure is admitted at the
foot of a pipe already submerged in the well. The air does not merely
bubble through the water, as might be supposed, but passes up the pipe
as a mixture of air and water. The introduction of the air into the
rising column of water makes the latter as a whole less dense than
the water around the tube, and therefore we have a difference in head
between the internal and external columns of water which will carry the
internal column considerably higher than the external column.
As the lifting force depends upon the “head” of water outside the
rising main, it follows that the maximum height to which the water can
be raised depends upon the depth to which the air pipe and rising main
are submerged below the standing level of the water in the bore-hole.
In other words, the greater the lift, the greater the depth to which
the air pipe must be carried before releasing the air into the rising
main.
Experience shows that the water pipe should be submerged 18 ins. for
every 1 ft. lift above the water level in the bore-hole, and allowance
must be made for the “depression” of the water level in the bore-hole,
which will probably take place when pumping is in progress. This
depression will vary according to the water bearing capacity of the
strata, in which the hole has been bored, hence it is necessary to go
carefully into the conditions before boring the hole. If available,
data should be studied concerning the standing water level, and the
pumping depression in other bore-holes in the immediate neighbourhood.
Also tests should be made before the boring machinery is removed
because, although the initial depth of bore-hole may be satisfactory
on the basis of standing level calculations, it may be found that when
pumping the depression is so great that the bore-hole has to be carried
to a greater depth.
The air is supplied at a pressure suitable for the conditions, and can
be carried down a separate tube and connected to the rising main at the
correct depth (Fig. 33), or, as is often done, one pipe may be lowered
and the rising main supported centrally inside the casing tube, the
annular space between the two being used as the air pipe (see Fig. 34).
The amount of free air required is from 0·6 to 1·0 cu. ft. per gallon
of water raised per min., provided that all the details have been
studied carefully and the design of the plant worked out accordingly.
If the air pipe is too small the air will bubble slowly through the
water, while if it is too large it will blow out with great force,
spraying and losing the water: the ratio between the cross-sectional
area of the air and water pipes is about 1½ to 4.
Advantages of air-lift pumping are that a greater amount of water can
be obtained from a hole of given size than by ordinary pumping; and
that one compressing plant can deal with several wells instead of
needing a separate pump to each well.
AIR-LIFT PUMPING
[Illustration: FIG. 33.—AIR PIPE OUTSIDE RISER.]
[Illustration: FIG. 34.—AIR BETWEEN CASING AND RISER.]
The disadvantages are, that the mechanical efficiency is low; that
a considerable amount of air is entrained in the water, and aerated
water is very unsuitable for boiler feed purposes; and that means
must be provided to allow air to escape by passing the discharge from
the pump over a weir or similar contrivance. It is necessary to have
some reliable form of oil trap between the compressor and the well to
prevent contamination of the water by oil carried over by the air from
the cylinders of the compressor; this is difficult, because the oil is
not only “atomized” but is actually vaporized while in the compressor
cylinders and as a gas it is difficult to reclaim. The air must be kept
as low in temperature as possible, and it is usually passed through a
cooler before being delivered down the well.
At times, air-lifts are installed for conveying other liquids to a
height, and when these can be treated at a high temperature it is
advisable, as the efficiency is then much improved. Even under these
conditions it is advisable to cool the air to the lowest feasible
temperature, before using it as a lifting medium.
When starting up, the column of water in the rising main has to be
moved as a solid column, and consequently a higher pressure of air is
required at starting than when the column has been set in motion, as
the water and air then pass up in alternative “pellets.”
In chemical works and allied industries this pneumatic method is
frequently used for pumping acids, and other corrosive liquids from
one place to another. Compressed air is a very handy medium for this
class of work as ordinary mechanical methods are ruled out, due to
the impossibility of introducing corrosive liquids into the pumps and
syphons unless great expense is incurred by the use of acid-proof
materials.
The air-lift is also very advantageous for pumping water which contains
a large amount of sand or similar gritty material which would cut
and score the walls of an ordinary piston pump. Air-lift pumping is
frequently used, therefore, on new bore-holes until the sand, etc., has
been eliminated, after which the final pump can be installed without
fear of damage.
The question of submergence will frequently make it impossible to
use air-lift without boring many feet deeper than would otherwise
be necessary, but when the water bearing strata is low this form of
pumping is frequently very convenient.
=Miscellaneous Applications of Pneumatic Conveying.= Several other
interesting applications of pneumatic conveying may be enumerated but,
being somewhat outside the primary scope of this book, they will not be
discussed in detail. The main object of the author is to raise interest
in the handling of solid materials in a manner practically unknown to
the general reader.
The housing problem has developed the _pneumatic handling of cement_
in a liquid form, and houses are now being built of reinforced cement
in the following manner. An expanded steel frame is supported between
concrete or brick piers, and on wood sheeting where necessary, and
liquid cement is blown on to the metal in the form of a liquid spray:
the first coat dries quickly and leaves a certain amount of cement
covering the framework. Then follows another coat, and again another
and so on, until the whole of the framework has been covered to an
appreciable thickness. The result is a thin wall or slab of cement
reinforced with the steel and of great combined strength. Slightly
domed roofs constructed in this manner have proved very strong and
durable.
The _Aerograph_ is an instrument working on the same principle for the
application of paint, and it is used a great deal in the art world, in
the manufacture of Christmas cards, in panel painting, and in interior
decoration generally. Excellent “tones” and shades are obtained by the
simple method of varying the thickness of the colour or the number of
coats applied. It is usual to convey the surplus colour and fumes away
from the operator by means of a stream of air through a special hood
placed at the back of the work, thus maintaining clean pure air for the
operator.
A similar machine of more crude design is used for whitewashing
walls of stables, cattle pens, etc. All these plants comprise an air
compressor, either power or hand operated, from which the air is led
to a special injector which draws up through a second pipe a certain
amount of the material to be sprayed. The paint or other material is
then atomized and impelled with considerable force on to the surface to
be covered.
The _sand blast_ is another application of pneumatic conveying in
which the medium conveyed is sand, which has well-known cutting and
erosive effects when it impinges on a surface at high velocity. This
plant is used for decorating glassware, obscuring sheet glass, and also
for cleaning stone buildings by the actual removal of the face of the
previously discoloured stone.
The _pneumatic conveyance of energy_ is exemplified by rock drills,
riveting machines, coal-cutters and innumerable other portable tools.
Energy is expended in compressing air which is transmitted through
pipes and made to yield its stored energy by driving the air motors of
the tools or other apparatus in question.
=Conclusion.= Enough has been said to show that pneumatic conveying
has made great progress, and that the possibilities of this method of
dealing with the moving of solid materials are much greater than has
been generally recognized.
Almost anything that will enter a pipe up to about 9 ins. diameter can
be conveyed in this way, either by “blowing” or “suction” or by the
“induction” method.
Weight and size is an advantage rather than otherwise, and bricks can
be dealt with more successfully than flour. The writer’s experience,
in the results of actual working with pneumatic conveying, indicates
that no problem should be considered too difficult to be tackled by
this method, and that even the most unlikely materials can be conveyed
successfully by pneumatic means.
BIBLIOGRAPHY
Readers wishing to amplify their knowledge of pneumatic conveying may
find useful the following references—
“Pneumatic Dispatch,” by H. R. Kemp, M.I.C.E., M.I.E.E., M.R.M. Paper
before the Inst. of Post Office Engineers. October, 1909.
“Power Plant for Pneumatic Tubes in the Post Office,” by A. B. Eason,
M.A., A.M.I.E.E. Paper before the Inst. of Post Office Engineers. 18th
October, 1913.
“Portable Plant.” Editorial article in _Cassier’s Engineering
Monthly_, June, 1919.
“Pneumatic Handling Machinery.” _Engineering and Industrial
Management_, 5th June, 1919.
“History of Conveying,” by G. F. Zimmer, A.M.I.C.E. _Engineering and
Industrial Management_, July to Sept., 1920.
“Boots as Power Users,” by E. G. Phillips, M.I.E.E., A.M.I.Mech.E.,
describing the coal handling plant used by Messrs. Boots Pure Drug
Co., Ltd., Nottingham. _Power User_, March, 1920.
“Pneumatic Handling Installation for Calcium Sulphide,” by G. F.
Zimmer, A.M.I.C.E. _Chemical Age_, 10th April, 1920.
“Pneumatic Conveying of Granular Substances, including Chemicals,” by
G. S. Layton. Paper before the Society of Chemical Industry, Third
Conference (Birmingham), 23rd April, 1920.
“Pneumatic Conveying of Coal and Similar Substances,” by J. H. King,
M.I.Mech.E. Paper before the Society of Chemical Industry, Third
Conference (Birmingham), 23rd April, 1920.
Instructive catalogues on this and allied subjects are issued by
the following firms (amongst others): Messrs. Ashwell & Nesbit,
Ltd., Leicester; R. Boby, Ltd., Bury St. Edmunds; H. J. King & Co.,
Nailsworth, Gloucester; The Lamson Store Pneumatic Co., Ltd., London;
and The Sturtevant Engineering Co., Ltd., London.
INDEX
Advantages of system, 5
Aerograph, 101
Air compressors, 67, 70, 71
—— filters, 10, 21-27
—— induction, 63
—— lift, advantages, 97
—— ——, air required, 97
—— —— “depression,” 96
—— —— pumping, 95-100
—— —— submergence, 96, 100
—— receivers, 69
—— reheating, 68, 69
—— velocity, 36
“Aquadag,” 20
Ash handling, 58, 74-77
Bag filters, 22-24
Bends and elbows, 34, 35, 67
Bibliography, 105
“Blowing” system, 4
Breaking of materials, 34, 35, 67
Buffer boxes, 78
Capacity of pipe lines, 36
Cement handling plants, 101
Cleaning with air blast, 94
Coal-handling plants, 54-58, 60, 61
Comparative costs, 53
Conveying above atmospheric pressure, 6
—— below atmospheric pressure, 6
—— above and below atmospheric pressure, 6, 64-66
Cyclone separators, 21
Design, factors influencing, 8
Despatch tubes, 80, 81
Dischargers design, 10, 28-32, 56, 57
—— difficulties, 9
—— valves, 28, 31, 32, 56, 58
Exhausters, 10, 14
Factors influencing design, 8
Flexibility, 5
Flexible suction pipes, 36
Floating plants, 3, 46, 51, 59-61
Flue cleaning, 59
Foot power pumps, 86
Fundamental principles, 3
Grain-handling, 45, 47
Heavy commercial systems, 7
High pressure systems, 6, 39
Historical, 1, 2
“Induction” system, 4, 6, 62-66
“Intermittent” tube system, 81, 83
Junctions in pipe lines, 33
King’s exhauster, 10-14
—— three-way valve, 37
“Kinking” to be avoided, 92
Large pipe systems, 7
Lime washing, 101
Low pressure systems, 6
Lubrication, 20
Materials, breaking of, 34, 35, 67
Mollers’ air filter, 24
Nash hydro-turbine, 18, 19
Nozzles (suction), 10, 40-43
Oil contamination, 11
Pipe lines, 10, 33, 36, 39
—— ——, capacity of, 36
Pneumatic tube carriers, 81, 82
—— ——, “continuous,” 81, 83
—— —— foot power, 86
—— ——, “intermittent,” 81, 83
—— ——, power required, 84, 85
—— —— pressure system, 81, 85
—— —— vacuum system, 84
Portable quay-side plant, 5
—— railway plant, 49-51
—— vacuum cleaners, 92
Power required, 44
Pressure systems, 4, 6
Pumping by compressed air, 94, 95
Quayside plants, 51
Reheating compressed air, 68, 69
Rotary blowers, 14, 15
Sand-blasting, 102
Stationary plants, vacuum, 92
Steam consumption, 72-74
—— jet conveyors, 72, 74, 76
—— jets, 77
—— jets, economy of, 72, 73
Sturtevant blowers, 16, 17
“Suction” nozzles, 10, 40-43
—— systems, 4-7
Systems, advantages of, 5
Telescopic pipes, 38
Turbo-blowers, 11
Vacuum cleaners, 89
—— ——, tests, 92
—— required, 3
Valves in pipe line, 37
Velocity of air in pipes, 36
Water pumping, 95-100
Waterside plants, 45, 47, 48, 59
Wear of pipes and bends, 34, 35
Wet air filters, 25-27
_Printed by Sir Isaac Pitman & Sons, Ltd., Bath, England_
Transcriber’s Notes
pg 59 Changed: await the convenience of the wagons
to: await the convenience of the waggons
pg 69 Changed: practice to instal an efficient separator
to: practice to install an efficient separator