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the Ian.

"And lei the length of the vanes be onc»fourth of the diameter of the fan.

"In adopting this mode of construction, the area of the inlet openings in the sides of the fan-chest
will be the same as the circumference of the heel of the blade, multiplied by its width ; or the same
area as the space described by the heel of the blade.

"The fc^owing table gives the sizes of fans varying from 8 to 6 feet diameter:

TABLE or BUVT PEOPOETIONB OF WANS,

DteMtarorPkn. Width oTVane. Length of Vane. Diamaler of inlet opaninK.

ft.ln. (tin. fUin. fLin.

3 9 9 1 6

8 6 lOi lOi 1 9



4 1 1 2

4 6 1 li 1 U 2 3

5 1 8 1 8 2 6

6 1 6 1 6 8

"I recommend the proportions in the above table for density ranging from 8 to 6 oz. per square
faich ; and for higher densities, viz., from 6 to 9, or more oz., the sizes given in the following table :



ft


in.





9





lOi


1





1


H


1


8


1


6



oTFan. Widtti of Vana^ . Lai^ttiorYane. Diameter of inlet opanii«.

ftin. A. in. ft.ln. ftin.

8 7 1 1

8 6 8i 1 U 1 8

4 9i 1 H 1 6

4 6 lOi 1 ^ 1 9

6 1 1 6 2

6 1 2 1 10 2 4

" The dimensions of the above tables are not laid down as prescribed Imaits, but as approximations
obtained from the best results in practice.

" Experiments were also made with reference to the admission of air into the transit or outlet pipe.
By a slide the width of the opening into this pipe was varied from 12 to 4 inches. The object of
this was to proportion the opening to the quantity of air required, and thereby to lessen the power
necessary to drive the fan. It was found that the less this opening is made, provided we produce
BoiBcieDt blast, the less noise will proceed from ^e fan ; and by making the tops of this opening
level with the tips of the vane, the column of air has little or no reaction on the vanes.

** As to the pressure of the blast commonly required in smithies, the range is from 4 to 6 oz. per
square inch. And an ordinary eccentrically placed fan, 4 feet diameter— the blades 10 inches wide
and 14 inches long, and making 870 revolutions per minute — will supply air at a density of 4 oz. per
square Inch to 40 tuyeres, each being l|-inch diameter, without any falling off in density."

The following table* gives particulars of some expenments made with a large fan used to blow the
copdas, etCL, at the London Works, Birmingham, England. Although in the early experiments only
$6 to 50 per cent of useful effect was reached, eventually as much as 76.16 was obtained. No

a Ftom "A Pnetkal Traatiae on Caatlng and Founding,'' by £. Bpretaon (London, 18T8).



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152



BLOWERS.



allowance was made for obstraction in the fire, bat the area of the tuyeres was taken, having taper
pipes leading to them, and the velocity of the air, multiplied by the pressure, was taken to represent
useful effect in horse-power.



ResuUi of Experimentt with Common Fcm».



NO. AND SIZS or
BLADES.



6 Bladea, with oen-
tre pkte, 16 x 8

4BlAde6, 16x12..
4Bkdet,16 x 8...

4 BkdM, 18i X li.

4 BiMlM, \%\ X 10.
4BIadei,16 x 13..
4Blades,17 x 12..
4 Blades, 16x11..-



n



,T12.6

!5i4!28
678. 5T
712.5



I'



12819

'8si3.9
9921.2
12812

11192




11858
9954
7740
8646
9678

10988

10285

10928
9!45S

10500
W74

10285
98n

10286
9474

10140
9178



6 6 128
6* "6* 192
6"6 i28



6



6



219
182.6

in

204
i76



li

I



64.81

74.5

41.

48.4

68.5

51.6

51.2

47.5

55.8

51.8

56.9

51.9

56.1

51.

57.

50.

54.7



26.7

22!is
25.66
28.7



26.



22.1
97.6



97.88
VIA



28.84



87.6

47.7

18.56

22.78

84.8

22.9

25.28

27.5

88.78

24.2

80.7

24.

28.76

28.25

29.1

24.5

26.41



► .go*



1'



18.6
25.8
6.9
9.68
28.87
12.28
17.22
15.00
24.78
15.25
21.99
15.18
21.81
16.97
21.9
18.7
19.97



86.1
64.
87.17
42.96
67.1
58.4
68.0
70.1
78.4
68.0
71.6
63.5
I 74.1
168.68
74.2
'68.8
75.16



A considerable difference in the amount of useful effect was sometimes produced by the sune
power ; but this arose either from a difference in the area of opening or in the pressure. When the
pressure was great, the result was generally affected, it being easier to get a moderate pressure with
a fan than a high one. A 74nch column of water is considered ample for cupolas. In all cases
indicator figures were taken in order to arrive at the power employed, and figures were also tiUcen
separately without the fan, in order to get at the friction of the engine and shafting. The fan-case
was an arithmetical spiral, so that the blades delivered the air r^vdarly. The following rules were
deduced from the experiments :

That the fan-case should be an arithmetical spiral to the extent of the depth of the blade at least

The diameter of the tips of the blades should be about double the diameter of the hole in the
centre ; the width to be about two-thirds of the radius of the tips of the blades. The velocity of the
tips of the blades should be rather more than the velocity due to the air at the pressure required, say
one-eighth more velocity.

In some cases, two fans mounted on one shaft would be more useful than one wide one, as in
such an arrangement twice the area of inlet opening is obtained as compared with a single wide fan.
Such an arrangement may be adopted where occasionally half the full quantity of air is required, as
one of them may be put out of gear, thus saving power.

Fans are less expensive in first cost and repairs, for a given duty, than blowing-engines ; but when
high pressures are required, they take somewhat more power to drive theuL In other words, the
fan is not an economical machine, in the sense of useful effect for a certain power ; and its useful
effect or " duty *' decreases rapidly as the speed is increased for the purpose of increasing the pres-
sure of blast. The power for driving a fan or fans is generally best given by a small high-pressure
engine, communicated by a belt.

The engine should run at a quick speed, and be provided with a tolerably heavy fly-wheel, to pre-
vent its running away in case of any accident to the driving-belt or fan. In order to get an increase
of speed from the engine, the fiy-wheel may be driven by a sun-and-planet motion inst^ of a orank ;
this will give two revolutions of the fly-wheel shaft for each double stroke of the piston, and then,
with a large pulley on the fly-wheel shaft, and a small one on the fan-axle, a high speed can be ob-
tained. But for many reasons it is unadvisable to use the sun-and-planet motion, if it can possibly
be avoided. If a large volume of blast is required at a moderate speed, this can best be obtained
by employing a fan of large diameter, driven at a moderate speed ; but where a high pressure or
great velocity of blast is desired, it is necessary to drive the fan rapidly.

It is not advisable to construct a fan larger than 8 feet in diameter, and for most ordinary pur-
poses one of about 5 feet diameter across the vanes is to be preferred.

A silent fan can only be obtained by having vanes which do not fill the casing, having the vanes
placed eccentrically in the casing, and forming the casing in a true spiral.

Provide ample apertures for the entrance and exit of the air, avoid sharp turns or projections in
the casings, and, in designing and fitting up the fan, all the moving parts must be securely fixed in
position, so that they will be able to withstand the great centrifugal force brought on them when
driven at a high speed, as, if any part becomes detached during working, great damage and probable
loss of life would ensue.

Fans, especially when largo and driven at a high speed, should be walled in all round, and every
precaution adopted to avoid loss of life, in case of any accident occurring to the fan while it is in
motion. The castings for fans should be made massive, as tending to reduce the vibration felt when
fans are worked at a high speed.

In fan-machinery, simple as it is, it has been found that monthly and even weekly repairs have
been hicurred, in oonsequenoe of the want of exact balance among the parts of the fan upon its



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BLOWERS.



153



ftile. With careful management in the first construction, this source of annoyance maj be entirely
renored. Another great fault consists of injudicious methods of *^ bringing up the speed " with too
great rapidity, with a view to which it was certainly necessary to make use of as few intermediate
•hafts as possible, which of course requires that large pulleys shall drive proportionally smaller
poUeys than if the rate of the reduction of speed were more moderate. On the other hand, the
experience of many founders proves that by moderately attaining the speed by the use of a greater
noinber of intermediate belt-pulleys, repairs of any importance are not incurred for mouths and
eren years. The great evil of too rapidly raising the speed is the liability of the belt to slip upon
the drums; for when slipping occurs, especially am<mg the slower parts of the motion, the belt is
nbjeeted to sudden and violent strains, caused by its unequal hold upon the rim of the drum. The
Qsotl remedy for this state of things is to apply rosin and pitch to the acting surface of the belt to
give it a bold. But the best plan is to employ spur-gear in the slower parts of the motion, and
bnMd belts and pulleys of conveniently laige diameters for the rest.
The following notes on the construction of fans will be found of practical utility :
Good Proportioru, — ^Inlet = ^ diameter of fan. Blades = i diameter of fan each way. Outlet =

area of blades

area of blades. The area of tuyeres is best when about = - — n — iv ,— t — r-; and

density of blast, oz. per sq. m.

it should not exceed twice this area.

The velocity of the circumference for different densities of blast is as follows, in feet per second
mdooDoes per indi: 170, 8 ; 180, 4 ; 196, 5 ; 205, 6 ; 215, 7. A proper speed for cupolas is 250
to 800 feet per second.

To fold the Horse-power required for a Fan, — ^D = density of blast in ounces per inch. A = area
of diseharge at tuyeres in square inches. Y = velocity of circumference in feet per second.

V*

X D X A

' = horse-power required.

963
Tojmd the Dmnty to he obtained with a given Fan^-^-d = diameter of fan in feet.

(I)"



120 xc;



= density of blast in ounces per inch.



TabU^




Vtlodty
Feet POT SeeoBd.


AlMOfNOKlM.


DMultyof

BUsk
Oi.perIiioh.


150

u
u

170
200

820


Twice area of blades
Equal I

*


1
9
8
4
4

6



TM duneing the quantity of AtTy of a given DentUtfy delivered hy a Fan, Total area noalee in
square feet x velocilg in feet per minute^ corresponding to density (see table) = air delivered in cubic



fid per minute.





D«dty.

O^per

Sqamljiob.


Vtlodty.
FMt pOT Miooto.


Deotlty.

Lb..p«r

Squuelneh.


Velocity.
FMtpOTMinoto.


D«,.Hy.

Lb«.p«

SqiuralDch.


Vdoaty.
FMt pw Mlnata




6,000
7,000
8.600
10,000
11,0(¥)
12,250


7
8
9
10
11
12


1S,200
14,160
16,000
16,800
1(^500
17,800


1

I*
f

4


20,000-
24,600
28,5500
81.600
84,640
40,000


6

8
10
12
15
20


49.000
66.600
68.200
6y,280
7N.000
69,400



^ Competitive Tests. — ^The pressure-blower has an advantage over the fan in its delivery of a posi-
tive or force blast measuring accurately the amount of air delivered per revolution. The blast does
not depend, aa in the fan, upon centrifugal action, nor upon the specific gravity of the air, to give
a definite displacement. When the proper amount of air is supplied the combustion in a cupola fur-
Baoe is perfect, and the highest rate of melting attained ; but as the carbon converts the oxygen of
the air into carbonic acid on its entrance at the tuyeres, so this compound is rapidly reconverted
faito carbonic oxide as it ascends through the charge. In order to secure the highest temperature
and efficiency, enough of this oxygen must be continuously injected to prevent the formation of car-
bonic oxide, and this can only be done by a machine which delivers positively under all conditions of
the furnace a fixed quantity. In conducting competitive tests between pressure-blowers and fans, the
foDowini^ formulse and arrangements have been employed : Both blowers were placed so that they
eould be driven from one and the same shaft, to which the djmamometer was applied. The number
of Terolotioiifl of the dynamometer-shaft was counted by an apparatus expressly built for the pur-
pQM. Eadi blower was provided with dovetail guides, to which four different slides were fitted, air-



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154



BLOWER&



tight These slideSf oontaining the discharge-openings of 6, 4|, 8|, and 2^ inches diameter, respec-
tively, were made of 1-inch thickness, and fitted to each blower. The pressure of the air was meas-
ured by a water-colunm, attached in such a manner and at such a place as to be affected properly by
the pressure. The motive power was supplied by an overshot water-wheel, the gate of which could
be moved at a place in the experimenting-room, where the pressure-gauge could be observed.

The manner in which the tests were made was the following : After the slide with the discharge-
opening was attached, the speed was regulated so that the water-gauge indicated the pressure re-
quired. While the water-column was carefully kept at the same height, the indications of the dyna-
mometer were read off and noted. Experiments of this kind were made with each blower, and*
conducted with openings ranging from 6 to 2^ inches, and corresponding pressures from 4 to 16f
ounces. It is evident that, through the same opening and at the same pressure, an equal volume of
air would be discharged by either the blower or the fan. It is also evident that the horse-power
indicated by the dynamometer, under the above conditions, would demonstrate the relative power
required by each blower to produce a given result, and show the comparative efficiency of each machine.

The volume of air discharged per minute was calculated from the f ormulsB :

V=e. — ftO^A^A. F=: c. ;;^ 60 y^64.32 x 1,782/). V^UOcA.a/p,



144



144



In which F, the Tolume of air discharged per minute in cubic feet, reduced to atmospheric pre^-
nre 29.9 barometer, and a temperature near freezing-point Ay the area of discharge-opening in
square inches. ^, acceleration of gravity = 82.16. A, height of column of air of one square indb in
section, and of a temperature near freezing-point, weighing p — ^pounds — in feet, p^ pressure of air
in pounds per square inch, e, coefficient of effiux, depending on the shape of the discharge-opening,
and due to contraction and friction. This coefficient was estimated by interpolation of the values
given by Prof. F. Wcisbach. c = 0.6.

The useful effect, or the work done, was assumed to consist in giving the velocity V 2 ^ A to the
air discharged, and was calculated from the formulae, viz. :

1 / 144 1

Useful effect in horse-power : 11= e, ». A a/ 2gh= © F = p F.

660 r "^ 33,000 __ 229r_

Example : Test No. 1 : Pressure of air in pounds = ^V = i=/>. Vo=V4=i- Area of dis-
charge-opening in square inches = 28.274 = A, c. = 0.6. Volume of air discharged per minute
in cubic feet = F= 140 <?. ^ V'p' = 140 x .6 x 28.274 x i = 1,186 cubic feet Useful effect in

„ pV ix 1,186

horse-power: H=z = = 1.294.

229^ 229i

Various Forms of Blowers.-— Fig. 351 represents a steam-blower devised by E. Eorting. It con-
sists, its principal parts, of an air-accumulator formed of a cast-iron tube opening below into a reser-

861.




voir, which serves at the same time as a base-plate. At its upper extremity the accumulator sup-
ports a dome, into which is fitted the blast-pipe 6, the nozzle of which is adapted to the opening into



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BOILERS, STEAM. 166



the toiithy fire. Immediately below this dome the steam-pipe tnivcrses the accumulator with an exit
it the oppodte end, as shown. At this end is the aspirator, formed of three cones, which admit air
in thdr interspaces, while the steam-jet is driven through the centre. The steam-loaded air passes
through a conical educUon-pipe into the reservoir, which serves as a base-plate, where the water of
00Dd«Dntk>n is parted with, and the heated current of air passes into the accumulator under a
tension corresponding to the dimensions of the aspirator multiplied by the pressure of steam. From
the aocomolator the blast passes through the nose-pipe at 6 to the smithy fire. In this manner a
blast is obtained, easily kept at any pressure, within certain limits, and at a temperature which very
nearly reaches that of the steam used. In the engraving, a is the steam inlet ; 6, the blast-pipe
opening from the accumulator ; c and «{, outlets for water of condensation.

For other Mowing-apparatus, see Air-Comprissors.

A simple form of blower is the 2'rompe, or WtUer-BUut, of which fig. 852 shows the prindple.

In this, a vertical tube of wood or iron, cylindrical or prismatic, of length and diameter suited to
the iall and quantity of water intended to be used, connects with a dstem below, made air-tight
except for the opening /, to connect with the tuyere. Through this tube a stream of water is allowed
to fdl, drawing in the air as it descends through openings that are indicated by broken lines in the
sides of the column, and breaking upon an altar below. The air thus carried into the cistern has no
Beans of escape except the tuyere i, and its quantity and pressure delivered through that depends
upon the absolute size of the column of water, and the proportions of the various parts. Yenturi
has already satisfactorily investigated the relations of this machine, which will not be dwelt on in
that aspect further here than to say that, although very cheap and convenient in its construction, it
nes more water for a given effect than a water-wheel would do, and that its effectiveness is quite
fimited. Earsten refuses to admit that the dampneta of the blast it affords injures the quality of
the iron ; ahbough it is probable that most metallurgists would conclude, in the face of general
theory and experience, that the good quality of iron made by this method exists in tpife of it.

The (heillatinff Cylinder of D'Aubuisson are cheap to construct, and worked with little power
and at onall expense. Although not giving a blast of sufficient amount /

of density for the smallest high-furnace, except with the most fusible
materialflj they answer very well for chafery and finery fires. Fig. 853,
which is a section of one of the cylinders, will afford an illustration of
tftdr action. A diaphragm, central, through the entire length and nearly
the whole diameter, is shown hXcd; vv are two valves, alternately as-
piring and expiring. In its normal position c <f is vertical ; the barrel is
filled half full of water, through a bung, and is then set in oscillation,
tiuoogh an arc of ttO or 100 degrees, by a connecting-rod and crank
geared on near e. It is manifest that in different angular positions of
we diaphragm the content of water in the two semi-cylinders will come
to be vnequal, as shown by the shaded lines ; and the air will be respec-
tivelj rarefied and condensed accordingly.

BOILER?, STEAM. The steam-boiler is a close vessel used for the generation of steam from water.
It has a furnace for the combustion of fuel— either inclosed within the boiler, as, for instance, in
loeomotive and the majority of marine boilers ; external, as in the case of land-boilers set in brick-
work ; or detached, the latter form of furnace being often used for the combustion of tan-bark, saw-
dust, and similar substances. Boilers are constructed of cast and wrought iron, steel, and copper.
Where wrought-iron, steel, or copper sheets are used in the construction, they are ordinarily fastened
t<^gether with rivets, and the joints are made tight by calking ; but in some instances the sheets are
gelded together, this last mode of construction having been recently introduced. Boilers may be
cither plam cylinders, or they may contain flues or tubes, so as to bring the water into more intimate
connection with the flames and heated gases issuing from the furnace. Until a recent period, nearly
til boilers, whatever their internal arrangement, contained inclosing-shells, as an essential part of
their construction. Of late years, however, what are known as sectional or water-tube boilers have
been introduced to a considerable extent In this class of boiler, there are a number of oonnected
Mctkns, eadi of which is quite small, and the inclosing-shell is not used. Hence the several parts
eMi be made li^t as well as strong ; and it is claimed by some that an explosion of a single section
ef ndi a boiler would be less disastrous than the explosion of a shell-boiler.

It is not possible, in the limits of the present article, to give a complete treatise on this important
Bobject, but the reader will find numerous references that will be of assistance in a more extended
leseardL

Combustion and FueL — Combustion, in the popular acceptation, is the union of carbon or hydro-
960 with oxygen, accompanied by light and heat Though this definition is far from being scien-
tifically exact, the word can be used hi this sense without impropriety, in treating of the combustion of
fiicL Some forms of fuel, it is true, contam sulphur, which also unites with oxygen during combus-
tkm, bat the proportion of this latter element is usually quite small, and its heating effect can be
i>*glected without serious error. The sulphur in coal is, however, occasionally injurious to the fire-
box of a boiler. The diief constituents of fuel are carbon, hydrogen, oxygen, compounds of these
«Jemcnts, and earthy matter. The principal varieties of fuel are wood, peat, coal (which may be
<fivided into lignite, bituminous, and anthracite), mineral oil, natural gas, sawdust, spent tan, straw,
•nd other refuse. There is generally some special arrangement of the furnace and proportions of
bofler that are best adapted for each form of fuel, as is explained more fully in another part of this
artade.

The reader who desires to thoroughly investigate the qualities of the chief varieties of fuel will
find a valuable collection of data in Dr. Percy°s "Treatise on Metallurgy." The remarks in the
\ article most necessarily be confined principally to coal, the fuel in common use.




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156 BOILERS, STEAM.



Mineral oil, when buraed under proper conditiona, is one of the most efficient forms of fuel, in
some cases about nine-tenths of its full calorific effect bdng utilized. An ordinary furnace can be
readily adapted to its use. An improved process for burning liquid fuel is described in the Engmetr-
ing and Mining Journal, August 7» 1876.

In localities where natural gas is obtained, this is frequently burned in the furnaces of bcnlers.

Peat, — Peat is used in this country as fuel to a very limited extent In Europe its applicatioDt
have been numerous, and a large amount of capital is invested in plant for its preparation, whidi
consists, generally, in drying and compressing it. Considerable information in regard to the prepa-
ration and qualities of this form of fuel is to be found in ** Peat and its Uses,** by S. W. Johnson;
** Report on the Utilization of Peat and Peat Lands," by F. A. Paget (in the " British Reports on the
Vienna Exhibition,'* and The Engineer, xxxix., x1.) ; in the ** Proceedings of the Institution of CivU
Engineers," xxxviii. ; in the ** Proceedings of the Institution of Mechanical Engineers," August, 1865,
and the ** Transactions of the Society of Engineers," 1864.

Coal, — The fuel most commonly employed in thb country b coal, and some little space will be
devoted to a consideration of the phenomena of its combustion. If a mass of coal is brou^t to a
sufficiently high temperature (probably 1,000° Fahr.), the combustible materials enter into combina-
tion. First, the water is expelled ; then the hydrogen in the volatile combustible matter unites with
oxygen, forming water ; and the carbon set free unites with oxygen, forming carbonic acid if the
temperature is sufficiently high and enough oxygen is present, or, under leas favorable circumstances,
forming carbonic oxide, or passing off unconsumed, as the coloring matter of black smoke, and being
deposited as soot The combustion of the fixed carbon next begins, and usually takes place as follows:
The first combination of the carbon with oxygen produces carbonic add, whi<^ in passing through the



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