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PITMAN’S TECHNICAL PRIMER SERIES
_Edited by R. E. NEALE, B.Sc., Hons. (Lond.)
A.C.G.I., A.M.I.E.E._
PNEUMATIC CONVEYING
PITMAN’S TECHNICAL PRIMERS
Edited by R. E. NEALE, B.Sc. (Hons.), A.C.G.I., A.M.I.E.E.
In each book of the series the fundamental principles of some
sub-division of engineering technology are treated in a practical
manner, providing the student with a handy survey of the particular
branch of technology with which he is concerned. Each 2s. 6d. net.
=THE STEAM LOCOMOTIVE.= By E. L. AHRONS, M.I.Mech.E.
=BELTS FOR POWER TRANSMISSION.= By W. G. DUNKLEY, B.Sc.
=WATER-POWER ENGINEERING.= By F. F. FERGUSSON, A.M.I.C.E.
=PHOTOGRAPHIC TECHNIQUE.= By L. J. HIBBERT, F.R.P.S.
=HYDRO-ELECTRIC DEVELOPMENT.= By J. W. MEARES, M.Inst.C.E.
=THE ELECTRIFICATION OF RAILWAYS.= By H. F. TREWMAN, M.A.
=CONTINUOUS-CURRENT ARMATURE WINDING.= By F. M. DENTON.
=MUNICIPAL ENGINEERING.= By H. PERCY BOULNOIS, M.Inst.C.E.
=FOUNDRYWORK.= By BEN SHAW and JAMES EDGAR.
=PATTERNMAKING.= By BEN SHAW and JAMES EDGAR.
=THE ELECTRIC FURNACE.= By FRANK J. MOFFETT, B.A., M.I.E.E.
=SMALL SINGLE-PHASE TRANSFORMERS.= By E. T. PAINTON, B.Sc.
=PNEUMATIC CONVEYING.= By E. G. PHILLIPS, M.I.E.E., A.M.I.Mech.E.
=BOILER INSPECTION AND MAINTENANCE.= By R. CLAYTON.
=ELECTRICITY IN STEEL WORKS.= By W. MACFARLANE, B.Sc.
=MODERN CENTRAL STATIONS.= By C. W. MARSHALL, B.Sc.
=STEAM LOCOMOTIVE CONSTRUCTION AND MAINTENANCE.= By E. L. AHRONS,
M.I.Mech.E., M.I.Loco.E.
=HIGH TENSION SWITCHGEAR.= By H. E. POOLE, B.Sc., A.C.G.I.
=HIGH TENSION SWITCHBOARDS.= By the Same Author.
=POWER FACTOR CORRECTION.= By A. E. CLAYTON, B.Sc., A.K.C.
=TOOL AND MACHINE SETTING.= By P. GATES.
=TIDAL POWER.= By A. STRUBEN, O.B.E., A.M.I.C.E.
=SEWERS AND SEWERAGE.= By H. G. WHYATT, M.Inst.C.E. M.R.S.I.
=ELEMENTS OF ILLUMINATING ENGINEERING.= By A. P. TROTTER, M.Inst.C.E.
=COAL-CUTTING MACHINERY.= By G. E. F. EAGAR, M.Inst.Min.E.
=GRINDING MACHINES AND THEIR USE.= By T. R. SHAW, M.I.Mech.E.
=ELECTRO-DEPOSITION OF COPPER.= By C. W. DENNY, A.M.I.E.E.
=DIRECTIVE WIRELESS TELEGRAPHY.= By L. H. WALTER, M.A.
=TESTING OF CONTINUOUS-CURRENT MACHINES.= By C. F. SMITH, D.Sc.,
M.I.E.E.
=ELECTRICAL TRANSMISSION OF ENERGY.= By W. M. THORNTON, D.Sc.
=STEAM ENGINE VALVES AND VALVE GEAR.= By E. L. AHRONS, M.I.Mech.E.
=MECHANICAL HANDLING OF GOODS.= By C. H. WOODFIELD.
=INDUSTRIAL AND POWER ALCOHOL.= By R. C. FARMER, D.Sc.
=POSITION AND DIRECTION FINDING.= By L. H. WALTER, M.A., A.M.I.E.E.
=HIGH TENSION TRANSFORMERS.= By W. T. TAYLOR, M.Inst.C.E.
LONDON: SIR ISAAC PITMAN & SONS, LTD.
[Illustration:
_Frontispiece_
INTAKE END OF PNEUMATIC CONVEYOR.
Adjustable to follow rise and fall of vessel on tidal waters.]
PNEUMATIC
CONVEYING
A CONCISE TREATMENT OF THE
PRINCIPLES, METHODS AND APPLICATIONS
OF PNEUMATIC CONVEYANCE OF MATERIALS
WITH SPECIAL REFERENCE TO THE CONVEYING
AND ELEVATING OF HEAVY SOLID MATERIALS
FOR ENGINEERS, WORKS MANAGERS,
AND STUDENTS
BY
E. G. PHILLIPS
M.I.E.E., A.M.I.MECH.E.
[Illustration: PITMAN’S
TECHNICAL
PRIMERS]
LONDON
SIR ISAAC PITMAN & SONS, LTD.
PARKER STREET, KINGSWAY, W.C.2
BATH, MELBOURNE, TORONTO, NEW YORK
1921
PRINTED BY
SIR ISAAC PITMAN & SONS, LTD.
BATH, ENGLAND
PREFACE
Pneumatic Conveying has recently attracted great and widespread
interest amongst engineers and others interested in the economical
handling of materials. The information hitherto available on the
subject has, however, been so meagre and so indefinite that the author
offers this concise treatment of principles, methods and applications
in order that those who are anxious to avail themselves of this
flexible means of transportation may know just how, and why, it is
worthy of their attention.
The high cost of labour, coupled with the desire to improve the
condition of the worker who has had to work in a dust-laden atmosphere
of an objectionable, or even poisonous nature, will create such a
demand for pneumatic conveying plant that present day methods of
transportation will be revolutionized in many branches of industry.
The author has had three years’ experience with one of the first
pneumatic plants erected in this country, for use with coal, ashes,
and flue dust, and he has conducted numerous experiments on other
materials, such as sand, oxide, potatoes, various chemicals, etc., and
has endeavoured to add his quota to the information available for the
benefit of other engineers and works managers.
Experiments proved that with certain materials the discharger was the
weak link in the chain, as wet sticky materials entering at a high
velocity “packed” tight and would not discharge freely. This led to
experiments which, with the valuable assistance of Mr. H. B. Clarke,
A.M.I.E.E., resulted in overcoming this difficulty by means which are
described fully in Chapter VI.
No attempt has been made to go fully into the questions of domestic
vacuum cleaners, removing dust from manufacturing processes, etc. The
chief aim has been rather to bring into prominence the flexibility and
other advantages of moving air as a means of conveying and elevating
heavy solid materials which hitherto it has been thought could not be
handled in this manner.
The author gladly acknowledges the interest and information given by
the following firms and individuals Mr. H. B. Clarke, A.M.I.E.E.;
Messrs. Ashwell & Nesbit; Boby, Ltd.; H. J. H. King & Co., Ltd.; The
Lamson Store Service Co.; and the Sturtevant Engineering Co., Ltd.
E. G. PHILLIPS.
NOTTINGHAM.
CONTENTS
CHAP. PAGE
PREFACE vii
I. SYSTEMS AND APPLICATIONS OF PNEUMATIC CONVEYING 1
II. DETAILS OF PLANT—PUMPS, EXHAUSTERS AND AIR FILTERS 10
III. DETAILS OF PLANT (CONTD.)—DISCHARGERS, PIPE LINES AND SUCTION
NOZZLES 28
IV. TYPICAL INSTALLATIONS FOR GRAIN 45
V. PNEUMATIC COAL HANDLING PLANTS 54
VI. THE INDUCTION CONVEYOR 62
VII. STEAM JET CONVEYORS 72
VIII. MISCELLANEOUS APPLICATIONS OF PNEUMATIC CONVEYING 80
BIBLIOGRAPHY 105
INDEX 107
ILLUSTRATIONS
FIG. PAGE
Intake end of Pneumatic Conveyor, with rise and fall
adjustment _Frontispiece_
1. King’s pneumatic system. Steam-driven air pump 12
2. Sturtevant rotary blower 17
3. Nash “Hydro-Turbo” exhauster 19
4. Sturtevant “Cyclone” dust separator 21
5. Automatic bag filter 23
6. Mollers’ air filter 24
7. Sturtevant wet filter 26
8. Fixed discharger with glass receiver 30
9. Sturtevant patent junction 33
10. Course taken by material round bend 35
11. Segment-back bend 35
12. Lobster bend 35
13. King full-way junction valve 37
14. Suction nozzles for high pressure systems 40
15. Sturtevant equipment removing wood refuse from double tenoning
machine 41
16. Sturtevant equipment removing dust from sand papering machines 42
17, 18. Ancient and Modern 46
19. Typical grain-handling plant 47
20. Floating pneumatic transport plant 49
21. Portable pneumatic plant on railway truck 50
22. Portable railway plant in operation 52
23. Pneumatic unloading of coal 55
24. Discharger for coal conveying plant 57
25. Brady steam jet ash conveyor 75
26. Typical Lamson inter-communication carrier 82
27. Tube central in wholesale drug house 87
28. Lamson distributing station 88
29. Stationary turbo-exhauster with dust separator 91
30. Portable turbo-exhauster 91
31. Suction cleaning for railway carriage cushions 93
32. Sturtevant equipment for office cleaning 93
33, 34. Air-lift pumping 98
PNEUMATIC CONVEYING
CHAPTER I
SYSTEMS AND APPLICATIONS OF PNEUMATIC CONVEYING
Conveying by mechanical means has existed for many centuries, and is
one of the earliest forms of man’s ingenuity towards labour saving
as we know it to-day. The pneumatic conveyance of materials from one
position to another, either horizontally or vertically, is the most
recent form of automatic handling of solid substances.
=Genesis and Applications of Pneumatic Conveying.= The need of water
for human consumption and for irrigation purposes caused the ancient
inventor to carry out nearly all his experiments with that substance,
and the first instance we have of anything approaching pneumatic
conveying is the well known injector in which steam is passed through
one pipe, placed at right angles to a second pipe, at such a velocity
as to reduce the pressure in the second pipe to below the atmospheric
pressure. The excess of atmospheric pressure over the reduced pressure
in the second pipe then drives up the latter the material (in this case
water) in which the end of the pipe is submerged. This invention is
about a century old, if it emanated from the Marquis Mammonry d’Eclet,
in 1818, as is usually believed.
The first practical application of this invention to other than liquid
materials is supposed to have been in connection with the conveying of
cotton in a loose form, as an improvement upon the manual shifting of
large bales. This development was made about 1867, and after this date
great progress was made, principally in connection with the handling of
grain, wheat, malt, etc., and largely owing to the work of an American
named A. K. Williams.
At the present day it is hardly possible to enumerate all the
successful schemes for the pneumatic handling of materials. In addition
to installations for the conveyance of materials such as those
mentioned above is the pneumatic tube, for conveying papers, messages
and cash in offices and between shop counter and cash desk, etc.
Also, there is the suction cleaner, ranging in application from the
handling of refuse and dust from saw mills and woodworking machinery
to the removal of fine abrasive and poisonous particles in certain
manufacturing processes. Small suction cleaners are, of course, now
quite familiar domestic appliances. The sand-blasting machine is really
another example of a self contained pneumatic conveyor on a small
scale.
Ashes, coal, oranges, sugar, chemicals, spent oxide, iron ore, spent
tanning bark, and many other materials are now actually transported,
elevated or conveyed pneumatically, and it must here be acknowledged
that the first really successful plant in this country was due entirely
to the initiative and inventive genius of Mr. Frederic Eliot Duckham,
late Chief Engineer to the Millwall Dock Co., who in 1888 commenced
experiments in grain-handling by suction. In 1892 he produced a very
successful floating plant for unloading ships into land silos, and this
installation was the prototype of many similar plants which were placed
in commission all over the world. Many improvements have been carried
out and numerous patents issued for pneumatic handling apparatus, but
the original scheme as designed by Mr. Duckham has never been departed
from seriously.
=Fundamental Principles and Components.= The pneumatic conveyance of
materials along pipes is most easily understood when the equipment
is considered as a pump producing a high velocity stream of air in
which the material to be transported is floating, and with which it is
carried through the pipe system. It is necessary fully to understand
this, as it is otherwise difficult to realize how it can be possible to
lift solids at the rate of 100 tons or more per hour, several hundred
feet up a pipe in which the vacuum does not exceed about 7 inches
mercury column (say, 11 lb. per sq. in. absolute).
A modern pneumatic conveying plant of the _suction type_ comprises:
(1) An _exhauster_, or an air pump, of either the reciprocating or
the rotary type. (2) A _suction nozzle_. (3) A _discharger_, whereby
the material is extracted from the pipe line at the desired position,
without “breaking” or losing the vacuum. (4) One or more appliances
for _filtering_ the air and extracting any foreign material which may
have been carried over from the discharger and which would damage the
cylinder walls of the exhauster if allowed to enter the plant.
It is necessary here to mention that all pneumatic conveying is not
done by exhausting, but frequently by the use of _pressure_, that is,
that the air is not sucked along the transport line but is actually
blown in under pressure by fans, air compressors, or rotary blowers,
according to the circumstances.
The _suction system_ is preferable when it is required to convey
materials from several outlying points to one central storage bunker
or area. On the other hand, the _pressure system_ is less expensive in
first cost, when it is required to transport from one central point to
numerous outlying plants in the area to be served. A combination of the
suction and pressure systems is now being developed for the handling of
materials in cases where neither the “suction” nor the “blowing” scheme
alone can be said to be successful. This combined system is known as
the _induction system_ and is discussed in Chapter VI.
=Advantages over Mechanical Conveyors.= The reasons why pneumatic
methods for elevating and conveying are now receiving such attention
are to be found in the advantages of pneumatic over mechanical
conveying. These may be summarized as follows: Economy in labour;
flexibility of plant both in design and operation; elimination of dust
and its harmful effects on the employees; and in many instances the
recovery of dust which is valuable and which would otherwise represent
a serious financial loss. Wear and tear on moving parts is reduced to
a minimum. All obstacles such as buildings, roads, rivers, railways,
etc., can be overcome easily since the conveyor is “only a pipe.”
Should circumstances not permit of a straight single run for such
appliances as bucket elevators, it is usually necessary to bag and
cart the material from one position to another, but this is avoided by
pneumatic elevating and conveying, because the pipe can be carried up
or down, round corners, over or under roads, etc.
Hundreds of instances still exist in which loose material in barges is
shovelled into bags, which are lifted by an ordinary friction hoist
into a building over the quay-side. The sacks are wheeled by manual
labour into the building, and emptied into hoppers or silos, the empty
bags being lowered again for a further cycle of operations. This costly
multiple handling may be obviated by the erection of a small pipe
line which will automatically feed itself at one end, and discharge
evenly and continuously into the receptacle provided. The whole of the
“moving parts” may be situated in one position, which enables them to
be carefully inspected, oiled and kept in repair, etc.
Cranes, hoists, telphers, and belt conveyors all have their special
spheres of usefulness, but no other plant can claim all the advantages
of the pneumatic system as outlined above.
=Pneumatic Conveying Systems.= As mentioned above there are three main
systems of pneumatic conveying, viz.—
(1) Conveying by air _above_ atmospheric pressure.
(2) Conveying by air _below_ atmospheric pressure.
(3) Conveying by air _above and below_ atmospheric pressure, by a
combination of (1) and (2), known as the _induction_ system.
Although these are the main headings under which the subject may be
considered, they must be sub-divided further as follows—
=(1) Conveying above Atmospheric Pressure.= (_a_) _Low pressure
systems_ using single-stage centrifugal fans, and suitable for
conveying such materials as wool, cotton, bark, chopped straw, paper
clippings, sawdust, shavings, jute, and fibrous materials of many kinds.
(_b_) _High pressure systems_ using multi-stage fans and blowers of the
rotary type or positive design, and suitable for conveying materials
of a denser nature such as dry sand, sugar, etc., also for pneumatic
despatch tubes.
(=2=) =Air Suction Systems.= (_a_) _Large pipe systems_ using ordinary
steel plate centrifugal fans, and applied to handling the waste
products and injurious dust in many industries, such materials being
sawdust and shavings from woodworking machinery; emery dust from
grinding wheels; dust and lint from polishing mops; leather dust from
heel and sole scouring plants; starch dust in confectionery works;
colour dust in works manufacturing pigments; and bronze dust in
printing works. Many other examples will no doubt occur to the reader.
(_b_) _Small pipe systems_ using multi-stage centrifugal fans or rotary
blowers. Under this section the most important plants are undoubtedly
those for domestic vacuum cleaning. Large stationary plants for this
purpose are installed in many hotels, offices, buildings, workshops,
theatres, large private houses, etc.
(_c_) _Heavy commercial systems_ in which the fan is replaced by
a reciprocating exhauster, producing currents of air suitable for
conveying such materials as coal, ashes, sugar, leather tanning bark,
ores, granite chippings, wood blocks, oranges, etc., which it would be
impossible, or undesirable, to pass through a fan.
(=3=) =Induction System.= A compressed air injector is used to produce
a partial vacuum on the suction or inlet end of the pipe system, and to
produce a pressure above atmospheric at the delivery end, thus avoiding
the necessity for a discharger. This system, which is suitable for use
with heavy sticky materials—such as hot sugar, saturated sand, finely
ground heavy ores, spent oxide as used in gas works, etc.—is now being
developed so as to make possible pneumatic conveyance of all manner of
materials which are unsuitable for passing through the discharger, or
air lock, of a suction system.
=Factors influencing Design.= In the strict sense of the term,
“pneumatic conveying” really implies the conveyance of a quantity of
material from one point to another, using air as the conveying agent.
As will be seen from the above, the subject also embraces the removal
of comparatively light dust produced in many industrial processes.
Although the same name is implied in both cases, the methods to be
adopted vary, and each case must be considered on its own merits.
With regard to a conveying plant proper, the points for consideration
in the initial stages are as follows—
(1) The nature of the material to be handled and the quantity required
in a given time.
(2) The size of the largest and smallest pieces of materials and the
density of the material.
(3) The distance over which the material is to be conveyed.
(4) The difference in level between the point at which the material is
fed into the system, and the point where it is delivered.
(5) The method and regularity of feeding the material into the system.
(6) The means to be adopted for separating the material from the
conveying air at the desired point of delivery.
There is a very important distinction between plants in which the
material passes _through_ the fan or blower and those in which the
conveying is carried out entirely under suction.
The latter system has many advantages, but it carries with it the
necessity of providing automatic delivery of the material without
seriously impairing the suction. In order to accomplish this, some
form of “air lock” is required, and a necessary feature of this is a
device with close-fitting surfaces or more or less air-tight valves.
The simpler plan is undoubtedly to pass the material through the fan,
as there is then no question of breaking the suction in order to get
the material out of the system. It is common practice to convey for
long distances such materials as wood chippings and sawdust, cotton,
jute, wool, esparto grass, paper chippings and many other materials.
In all cases, however, the designer is confronted with the problem of
separating the material from the air, and in many instances to do this
satisfactorily is more difficult than the actual conveying; especially
is this so with certain sticky materials or materials which will
readily “pack” or build up when entering any mechanical discharger at
the high velocity necessary in the suction system.