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Salt in Marine Boilers

From: Henry Evers, LL.D., Steam and the Steam Engine, London, William Collins, Sons, and Company, 1873. The author was Professor of Mathematics and Applied Science at the Charles Science School, Plymouth.

Notes: Page numbering and line breaks have been retained; images are found at the bottom of the page on which they may appear higher in the original text layout. While we endeavour to be accurate in our scanning and OCR precesses, the occasional error may have escaped our attention.

Also available in PDF format with the original layout, with the addition of the "Exercises" at the end of the Chapter.

CHAPTER X.

SALT IN MARINE BOILERS.

Sea Water—Specific Gravity—Boiling Point—Blowing Out—Scale—
Salinometer — Hydrometer — Priming — Feed Pumps—Giffard's
Injector.

183. Pure Water Should be Used.—Boilers, both land
and marine, are liable to become internally incrusted. If
these incrustations are not carefully removed or guarded
against great injury will ensue. All water contains solid
substances, whether it be lime, flint, salt, or sulphur, all of
which will either do, or be the means of causing, damage.
Marine boilers are generally fed with salt water. Hence
it is necessary to explain fully the constituents of sea water,
and how their evil effects may be guarded against.

The deposits and incrustations which are the source of so
much danger, are not likely to be retained as necessary evils.
If surface condensation, which, as we have already said, has
been introduced into some of our iron-clad vessels, be suc-
cessful, the condensed water, being free from all such matters,
will form no deposits. If the steam could be rapidly and
effectually condensed without mixing it with impure water,
it would itself supply almost enough water for feed, and that
of the purest quality. All the evils of deposits, incrusta-
tions, priming from impure water, and much of the wear
and tear of boilers, would be in many cases entirely and others
greatly prevented. The consumption of fuel would be less
than at present, and the air pump would be considerably
reduced in size, and therefore less power would be required
to work it, although of course we should have the circulat-
ing pumps instead, but still upon the whole there would be
a gain. As the condensed steam would contain no air, the

162     STEAM.

function of the air pump would be exclusively confined to
the removal of the condensed steam.

184. Sea Water is both salt and bitter. Everywhere the
sea holds in solution a large quantity of solid substances,
chiefly common salt or chloride of sodium. The amount of
salt is not constant in all seas, nor even in the same sea, nor
at all depths, varying according to the amount of evapora-
tion (i.e., the heat of the climate) and the quantity of river
water running into the sea. The Red Sea is Salter than the
Mediterranean, the Mediterranean than the Atlantic, the
Atlantic than the Pacific. The water of the northern
hemisphere is not so salt as that of the southern. The
position of maximum saltness in the ocean is about 22° N.
latitude and 17° S. latitude, and the belt of ocean lying
between. We may incidentally mention that this is the
region of greatest evaporation, and that therefore the saltness
of the ocean follows from that circumstance. The Polar seas,
Baltic, and White seas, contain very little salt. Ice is free
from it, because water in the act of freezing parts with all its
impurities. Out of every 1000 parts 34.4, or about 1/30 of the
whole consists of solid matter; out of the 34 parts nearly 24
are common salt. We may put it thus : out of 30 gallons of
sea water, 1 gallon consists of solid matter, and of this solid
matter 24/34 or 12/17 is pure salt; 24 parts out of 34.4 are pure
salt, 4 parts chloride of magnesium, 4 parts sulphate of
soda; 1 part in 1000 is carbonate of lime (chalk), and 1
part in 4000 silica (flint).

ANALYSIS OP SEA WATER.

Chloride of Sodium,...................................... 24
Chloride of Magnesium,................................. 4
Sulphate of Soda,......................................... 4
Carbonate of Lime,....................................... .34
Silica,......................................................... .080
Other substances,*........................................ 2.

                              34.426

* Bromine, Iodine, Boron, Silver, Copper, Iron, Potassium, etc.

BOILING POINT OF SALT WATER.     163

Professor Forchammer* gives the following as his analysis
of sea water :—

Carbonic acid gas is ever present in sea water, and its
quantity increases with the depth. There is also a trace of
ammonia with atmospheric air to sustain life in the propor-
tion of from 1/40 to 1/30 of its bulk. These facts, especially
that relating to the different quantity of salt in different
seas, go to explain the reason why the extent of the "brin-
ing" varies in different seas.

185. The Specific Gravity of sea water differs with every
sea. In the North Atlantic Ocean it is about 1.02664,
while in the South Atlantic it is greater, 1.02672. The
Indian Ocean has a specific gravity of 1.0263; the Red Sea,
1.0286; the Mediterranean, 1.0289.

186. Boiling Point of Sea Water.—In consequence of some
of the above solid substances being chemically combined and
the others mechanically suspended in sea water, especially
because of the latter, and its specific gravity being greater,
it takes considerably more heat to boil it than to boil fresh,
spring, or river water, and of course as ebullition continues
and the steam is used the water will get salter and salter; no
salt can possibly pass away with the steam, and therefore the
amount of heat required to convert the water into steam will
have to be increased in proportion to the density of the
water, while the water itself will become saturated with salt,
or it will be incapable of holding more salt, which will be
precipitated, and form a crust on the boiler, separating the
iron boiler plates from the water, so that the boiler plates can
actually become red hot and danger is imminent, for the
plates being softened they are liable to collapse.

187. Boiling Point of Salt Water.—Salt water contain-
ing part of salt (it has been usual in all works on steam

Chlorine,......... 19. parts.
Sulphuric Acid,.......... 2.26
Lime,............ .56
Magnesia,............ 2.10
All Salts,............ 34.04
Total parts, 58.32

* See Ansted's Physical Geography, p. 141.

164    steam.

to say will boil at a temperature of 100°2/3 C.; if the
proportion, of salt be doubled, or 2/30 it will boil at a tempera-
ture of 101°1/3 C, if 3/30 or 4/30 the boiling point will rise re-
spectively to 102° C. and 102°2/3 C.; when there are 12/30 of salt
in the water the boiling point rises to 107°7/9 C. 12/30 is the
point of saturation, when the water is so full of salt that it
will hold no more, and it is therefore rapidly precipitated.
It will assist the memory perhaps to state that in each gallon
of sea water there is more than four ounces of salt, and if
two gallons be boiled down to one, it will contain double that
amount, or more than eight ounces.

188. Blowing Out or Brining the Boilers.—Generally
the saltness of water in the boilers must be kept below three
or four thirtieths. To effect this, and to have them as free
from salt as is consistent with the economical consumption of
heat, the practice of "blowing out" is resorted to. For this
purpose blow out cocks are fitted to the bottoms of all marine
boilers, from the cocks pipes lead into the sea. Every two
hours, but generally less, the blow out cocks are opened, and
the supersalted water violently forced out of the boiler, by
the pressure of the steam, into the sea. Much heat is lost
by this blowing out, and many methods have been devised to
save it. Before showing how this is accomplished, we must
give other modes of getting rid of the impurities which
collect in a marine boiler. The brine is sent overboard,

(1) By Blow Out Cocks (already explained).

(2) By Brine Pumps.

(3) By Surface Blow Out and Scum Cocks.

189. (2) By Brine Pumps.—To many engines are fitted
brine pumps, and at every revolution of the engine a small
portion of brine is extracted from the boiler. The size of the
brine pumps must be such that the quantity of water drawn
off added to that evaporated must be equal to the quantity
introduced by the feed pump. If the water ejected from the
boiler is to contain 3/30 of salt, or three times as much as the
feed water, then, if the feed pump supply n gallons in a given
time, the brine pumps must extract n/3 gallons in the same
time. The rule is, blow out from 1/4 to 1/3 the amount of
feed water.

SCALE.    165

190. (3) Surface Blow Out and Scum Cocks.—The foreign
substances in a boiler are always buoyed up to the surface,
where they not alone prevent ebullition, but the formation
of steam. The steam rises from and around them, and they
remain at the surface for some time, when they gradually
descend and form a scale upon the tubes and flues. It is
therefore found quite as advantageous to blow out from the
surface as from the bottom of the water. It is done by
means of scum cocks, which are inserted on a level with the
water, and are kept constantly about one-eighth open the
whole of the time, so that as fast as dirty scum and other
impurities rise to the surface they are expelled.

191. Lamb's Surface Blow Out Apparatus is a very efficient
contrivance for effecting the same object. A float in con-
nection with the bottom of the discharge pipe regulates the
feed and discharge water. The apparatus ejects the scum
and dirt at once; but in some boilers sediment collectors are
employed, one, in shape and size somewhat resembling a sugar
loaf, is placed in each boiler with the small end or apex
downwards, it is connected to a pipe leading into the
sea to carry the sediment away. The top or base of the cone
stands out of the water, and the impurities enter through
longitudinal tapering slits being ballooned into the cone,
where the water is comparatively still, by the steam as it
rises to the surface. The object of all this is to save heat.

192. Scale.—-Whatever care and precaution are adopted,
scale can hardly be prevented from forming on the boiler
plates. A careful and attentive engineer can always reduce
it to a minimum. When scale is formed on the boiler plates,
it prevents the passage of heat into the water, for salt,
gypsum, lime, etc., are exceedingly bad conductors of heat,
and will not allow its motion to pass to the water, and
therefore a waste of fuel must arise. When water is satur-
ated with salt, etc., through negligence or otherwise, it
becomes heavier, and therefore takes more heat to boil it,
which is another waste of fuel; again, the scale is occasion-
ally so hard and solid that the plates become red hot, and
are liable to be burnt as well as to give way from internal
pressure. Ammonic chloride and other chemical substances
are sometimes put into marine boilers to prevent scale, but

166     STEAM.

the utmost they do is to precipitate the foreign ingredients as
powder, which must still be removed by blowing out. The
more of these substances there are in the water, the more
work the heat has to do to lift them, and therefore the more
heat is required for ebullition, which is waste of motion and
power.

A practical engineer, who has examined thousands of
boilers, says : "Much mischief is often done by the injudi-
cious use of compositions in the boiler which are designed to
prevent incrustations, especially where there is no blow off
cock or where its use is neglected. A hard deposit on the
boiler plates is, in the writer's opinion, not so injurious as
the soft and muddy deposit produced by the use of such
compositions. A hard scale ... is sufficiently mischievous,
but the injury to the plates is much more rapid when a
thicker but spongy deposit entirely prevents contact of the
water, and impedes the transmission of the heat. The money
spent in boiler compositions would be better applied in
securing a supply of proper water, or in filtering and purify-
ing the water before it enters the boiler. More attention
to the purity of feed water would nearly always effect
economy, and would be far cheaper than using chemical or
other ingredients to neutralize the impurity after it is in the
boiler. In many cases simply filtering the water in some
ready way has produced very great improvement." *

A simple illustration of the formation of scale may be
seen by examining the tea-kettle, where a scale (lime or
chalk chiefly) is left on the sides and bottom of the kettle,
because steam formed from impure water is perfectly pure;
it can carry nothing away with it. We may also consider
the boiler as, or compare it to, a great salt-pan. Just as in
Cheshire and Worcestershire salt is made by the simple
process of evaporating water in large pans, so does salt, etc.,
collect in marine boilers; but there is this difference, the
scale formed on boilers is not soluble in water, while salt is.
Here, of course, we draw a distinction between salt and
scale.

An effective and expeditious, but not very good plan,
to scale boilers is to throw in a few wood shavings
* From Marten's Steam Boiler Explosions.

salt and the boiling point.     167

all along the bottom, and set them on fire. They quickly
heat the scale, which expands more than the shell of the
boiler; the heat cannot reach the latter, so the scale is
loosened from the plates. Precisely the same process is gone
through, with a different result, when a glass tumbler is
cracked by pouring hot water into it. The heat in the water
suddenly expands the inside of the glass, which becomes too
large for the outside, and so the glass is broken. Any scale
that remains after this must be taken off with a hammer and
chisel. This hard incrustation is formed in layers, and of
course chiefly consists of carbonate and sulphate of lime,
gypsum and chalk, with common salt. We have by us
pieces of scale looking like pieces of iron; in their cross
section they have the appearance of very thin alternate bands
of iron and hard crystalline rock, while other pieces are pure
salt. On this point Mr. Marten says : "The practice, espe-
cially in certain districts, of emptying the boilers immediately
the engines are stopped, and before the flues have cooled, in
order to loosen the scale by overheating the plates, has
caused much more mischief than those who persist in doing
it will believe, and has nearly ruined some otherwise good
boilers."

193. Salt and the Boiling Point.—There are several
methods of ascertaining the amount of saturation of the
water in a marine boiler :—

(1) By the Thermometer.

(2) "    Hydrometer.

(3) "    Salinometer.

Prom what has been said it will be gathered that the boil-
ing point of water depends upon the quantity of salt in it, its
specific gravity, and the pressure of the air. The strength
of a solution of salt and water has always a fixed and well-
ascertained relation to the boiling point and specific gravity.
For water with

1/30 or 1° of saltness in it boils at 100°2/3C.
2/30 or 2° "    "         l0l°l/3C.
3/30 or 3° "    "         102° C.
4/30 or 4° "    "         102°2/3C.
5/30 or 5° "    "         103°1/3C.
10/30 or 10° "    "         106°4/9 C.
12/30 or l2° "    "         107°7/9C.

168     STEAM

And also as fresh water when the barometer stands at

27 inches boils at a temperature of 97°.2C.
28 "    "        98°.lC.
29 "    "        99°.1 C.
30 "    "        100° C.
31 "    "        100°.8C.

we see at once the truth of what was previously said, that
the boiling point of water depends upon its weight or specific
gravity and the pressure of the air.

If, then, water be taken from the boiler, and boiled in the
engine room under the ordinary barometric pressure of the
air, and it is found by using the thermometer that its tem-
perature at the boiling point is 103°23/9, we must at once con-
clude that there are 5 degrees of saltness in the water, and that
precipitation of impurities is commencing, and blowing out
must be resorted to at once. But if by the same process it
is ascertained that the water boils at 101°1/3 C. (in the engine
room), it is known that the boiler is comparatively safe and in
good working condition. Salt does not really deposit till 12/30

194. The Hydrometer tells us the amount of salt in water
by showing its specific gravity. The figure in the margin
represents one. B is a hollow ball of brass or
other metal, from which rises a stem C D,
graduated; A is a second globe filled with
mercury to make the whole swim uprightly
in the water. A acts in precisely the same
manner as the lead on a fishing line. The
lead keeps the float upright, so does A the
hydrometer. The stem C D is graduated that
we may read off how far the stem sinks in the
water. The greater the specific gravity of the
water, or the more salt there is in it, the less it
will sink, so the density is thus made a test to
exhibit the amount of salt. We read off (not
the density, but) the saltness of the water. Each hydrometer is graduated to a particular
scale, generally 55°; i.e., when placed in distilled water at a
temperature of 55° the hydrometer sinks to the point marked
55°. This is much too low, for when water is taken from
the boiler the experimentalist has to wait a considerable time

HYDROMETER

169    SALINOMETER.

for the water to cool down before he can test it. 90° C.
would be a far better temperature to select. We now see
the utility of the specific gravities of sea water given on page
163, and that the hydrometer is an imperfect instrument
without the barometer; so useless is the one without the
other, that we frequently see attempts made to combine the
two, as in the salinometer.

195. Salinometer. — The salinometer
has been presented in several shapes.
In one it consists of a thermometer and
hydrometer combined in a copper vessel,
in another, Seaward's salinometer, of two
pith balls. Mr. Seaward affixes a glass
tube fourteen inches long, in a similar
manner and in a corresponding place to
the glass water gauge, so that when at-
tached to the boiler the water rises up
from the bottom of the boiler through
the lower cock, and remains in the glass
tube at the same level as the water in
the boiler. The taps are then closed and
the upper one opened, and two small balls
of glass or metal are dropped into the
water. The specific gravity of the first
ball is such that it will sink when there
are five degrees of saltness in the water
and swim when more, the other ball will
sink when there are less than three degrees
of saltness, but swim when four or more.
By this method the state of the boiler is
soon ascertained.

How's salinometer consists of a cylindrical vessel, A G, con-
nected with the steam boiler by the pipe B; the connection
on the boiler being below the surface of the water. The
quantity of water admitted to the salinometer is regulated by
the cock C in pipe B. The salinometer is most usually fixed in
the engine room, so as to be in constant view of the engineer,
but it can be fixed in any other convenient place. A ther-
mometer D is placed in the cylinder A G of the instrument,
to show the temperature of the water. A hydrometer E

HOW'S SALINOMETER

170     STEAM.

floats in the water, at a height corresponding to the density
or saltness which it indicates, and is protected by the metal
guard H. An overflow pipe F takes away the surplus water,
and prevents it running over the top. I is a cock for empty-
ing the instrument through the pipe F. It should, of course,
be emptied as often as the water is tested.

198. Priming.—When the steam comes from the boiler
mixed with water, in the shape of spray or froth, it is said to
be primed. Priming exists under most diverse circumstances;
its cause cannot at all times be clearly traced.

197. Causes and Danger of Priming. — Priming takes
place more in new than in old boilers; when there is but little
water in the boiler; when the spaces between the tubes and
flues are contracted; when there is fierce ebullition, this cause
may be said to accompany all priming; in passing from fresh
water to salt or salt to fresh; when the water used is muddy,
dirty, or slimy; when there is too small a steam chest; when
a safety valve, being situated near the steam pipe, is suddenly
opened. The danger arising from priming is very great, and
should therefore be most anxiously guarded against. We
shall see its danger and injurious effect, if we but con-
sider that when it gets into the cylinder, and there accumu-
lates as incompressible water, something must give way
should the test cocks and escape valves act improperly.
Priming impairs the vacuum; in consequence of this, more
water will have to be used for condensation, which will
throw a greater load upon the air pump, and more feed water
will also be required.

198. Remedy for Priming.—As priming is generally ac-
companied with great ebullition, obviously the most effectual
remedy will be to enlarge the steam chest. It is found that
boilers with plenty of water surface, or with a large steam
chest, seldom or never prime. Cornish boilers with their
large water surface give no trouble by priming. A remedy
much practised with locomotive boilers, is to open a safety
valve remote from the steam chest and pipe. Other temporary
remedies are : to partly shut the throttle valve; to work the
steam at a high pressure; to open the furnace door, thus
checking the fierce boiling; to put down the stop valve so
that the steam rushes against it, and the water is knocked out;

171     REMEDY FOR PRIMING.

to inject tallow into the boiler by means of the donkey pump
or a syringe fitted on purpose, this is the favourite remedy, but
it is found in some boilers to increase the priming. Another
remedy is to fit a steam pipe in the boiler full of small
holes, and inside this another similar pipe, but to take care
that the perforations of one pipe are not opposite those of .the
other. The steam in entering dashes against the inside pipe,
and the spray falls out. Any thing that checks furious
ebullition, or allows the steam plenty of space to rise, checks
priming. When the steam chest has to be enlarged, it is
better to fit a second on the top of the old one. Priming
arising from the use of impure water may be obviated by
liberally blowing off from the surface until the nuisance is
abated.

A very good plan to prevent priming is one adopted in the
engines constructed by Charles Powis & Co. Their arrange-
ment is to fit the stop valve, opening to boiler, with a disc
plate, arranged with orifices on its upper side so that dry
steam only can find its
way through the stop
valve. A C is a section
of the disc plate fitted
inside the boiler; W L
is the water line, and
B B the top of the boiler,
so that all steam passing
to the stop valve, which
is situated just above
S V, must pass in the
direction of the arrows,
through the small per-
forations into which the
top arrows are entering. The water will be thrown and
knocked out of the steam before it can pass to the stop valve.

Boilers sometimes prime when the ship passes from salt
to fresh water or fresh water to salt. It has been suggested
that in passing from salt to fresh water the cause is this :
fresh water being lighter than salt, is upon its admission to
the boiler more easily thrown about by the ebullition, and
therefore more spray is flying; but as the same boiler will

ENTRANCE TO STOP VALVE.

172     STEAM.

also prime in passing from fresh to salt water, this reason
evidently will not hold; we have yet to seek the true cause.
May not the change of water cause a serious change in the
existing condition of the boiler, and this change being accom-
panied by a general disturbance of the equilibrium of the
water, much more spray is thrown off than usual, and prim-
ing follows.* When new boilers have primed, a good plan
adopted, is to run into harbour and blow out the boiler
several times in succession. This has often effectually pre-
vented priming.

199. Fire Grate Surface, Heating Surface, Amount of
Coal to Evaporate One Cubic Foot of Water.—
In the
majority of marine boilers, it is usual now to allow three-
quarters of a square foot of fire grate surface, and about
nineteen square feet of heating surface, to each horse-power,
but some take these numbers at half a square foot and twelve
square feet. It is also calculated that six pounds of coals
should be consumed every hour for each horse-power of the
engine; these proportions of fire grate, heating surface, and
consumption of coal, evaporate one cubic foot of water per
hour. Locomotive boilers are constructed with a much
smaller amount of fire grate surface; to compensate for this,
the waste steam pipe is introduced into the funnel, which
causes a most intense heat in the furnace, and it is found,
the more intense the heat, or the hotter the heating surfaces
and the water are, the more heat will pass into the
water. They consume one hundred weight of coke per
hour on each square foot of grate surface, the proportion of
heating surface to this is eighty square feet; on every five or
six square feet of heating surface one cubic foot of water is
evaporated per hour. Each horse-power requires a cubic
foot of evaporated water per hour, but in high pressure work
more. The quantity of water may be generally taken as one
cubic foot per horse-power per hour, but it is in excess for
such engines as those in which advantage is taken of the
expansive force of steam. In Cornish boilers, where an
enormous duty is obtained for each engine, not more than
three and a half or four pounds of coal is burnt on each

* See Causes of Boiler Explosions—Spheroidal Condition of Water,
and Water Purged from Air.

FEED PUMPS.     173

square foot of grate surface per hour. As well as a boiler
having a due proportion of grate and heating surface to pro-
duce the necessary volume of steam, the furnace must be
sufficiently roomy to consume all the products of combustion;
the tube or flue surface, etc., must be adapted to abstract as
large an amount of heat as possible, without too much passing
away as waste, while at the same time the water spaces in
the boiler and the distances between the tubes must be large
enough to allow the steam freely to rise, or else priming may
take place. Again, the furnaces should never be too long, for
the stokers will find a difficulty in keeping the bars free from
clinkers, the clinkers as well as the fire not being fairly
within reach.

200. Feed Pumps.—The feed is supplied to the boilers in
one of the following ways : (1) By boiler hand pumps; (2)
by the donkey engine; (3) by the feed pump proper; or (4)
by Giffard's injector.

(1) The boiler hand pumps are fitted to marine boilers, so
that when there is no steam up men may fill the boiler by
hand, providing it is not sufficiently below the level of the
sea for sea water to run in freely when the Kingston valve
is opened.

(2) The donkey is a small steam pump in the engine-
room that can be set to work to fill up the boilers when the
engines are waiting for orders. The donkey has always the
steam piston and pump piston at opposite ends of the same
rod.

(3) The feed pumps which have been already explained.
In stationary engines part of the warm condensing water
is driven into the boiler as feed; the rest, by far the greater,
quantity, being allowed to run away. But the feed pumps
should at all times be capable of supplying much more water
than the boiler in its normal state will use. The capacity
of the feed pump is generally about 1/240th that of the cylinder,
so that it can supply more than three times as much as is
required. While the steam pipe should be attached to the
highest point of the steam chest, the feed pipe should be
fixed as low down as possible, so that the cold water may
gradually rise. In most Government vessels the feed and
donkey pumps are made of brass.

174     STEAM.

201. Locomotive Feed.—In locomotives the feed pumps
are made of brass and the plunger
of iron or brass. They are worked
either from an eye on the back of
the eccentric (see fig., p. 70, G), or by
the piston crosshead. The passage of
the water from the tank to the boiler
is governed by three ball valves and
a cock or valve box close to the boiler.
The lift of the valves must never ex-
ceed ~g or of an inch. There are
generally two pumps to each engine.
The water, when directly admitted
to the boilers, enters about the
middle of the bottom, but some-
times a pipe passes it through the
smoke box first to extract as much
heat as it can from the heated gases
before it gains admission to the
boiler. So also in the marine en-
gine, the water sometimes enters
the boiler from round the funnel.

202. (4) Giffard's Injector.—
This is a novel contrivance for feed-
ing boilers, fast superseding all
other methods of feed; but no con-
vincing explanation of its action
has yet been offered. The manu-
facturers claim for it these advan-
tages :—

(1) It is as cheap as a pump and
its connections; (2) it saves the
wear and tear of pumps, which in
locomotives and other high pressure
engines are very considerable; (3)
it saves the power required to work
the pumps; (4) the water enters the
boiler at a high temperature, so no
heat is lost; (5) you can feed a
boiler without setting the engine in

GIFFARD'S INJECTOR.

page      175

motion, thus saving donkey pumps; (6) it is free from
risk of damage or stoppage by frost.

We will suppose it properly attacked to the boiler, it then
works in the following manner :—

GI is the injector, N is attached to the boiler. Steam
can pass into the injector at N. When the handle d is
moved up, steam rushes through a i at i, where it meets the
water supply coming into the injector at E. The steam
drives the water through n, and beyond the valve s, into
the boiler. When there is sufficient water in the boiler, the
valve s is forced upwards, and no more water can pass it;
the waste water can then pass through the overflow pipe L.
The steam to work the injector must be taken from the
highest part of the boiler, and must not be primed. The
water driven through it may be taken from a cistern over-
head, or from a tank in the ground; but the distance from
the level of the water below to E above must not exceed
5 feet. Now it is found that the pressure of steam will
actually drive the water into the boiler, although it has to
force it against the pressure of both the steam and water in
the boiler.

A jet of steam moving with perhaps a velocity of 1700
feet per second, is instantly condensed in perhaps twelve
times its weight of water. The combined jet will then
move, by the momentum imparted to it by the steam, at one-
thirteenth its former velocity, 131 feet per second—the
motion of the steam being wholly imparted to the water.
Thus the jet properly directed enters the boiler, and we
can find an explanation of the action of the injector by
simply considering that it acts solely by the momentum
imparted to the water by the jet of steam.

EXERCISES CHIEFLY FROM EXAMINATION PAPERS.

1. Why is the hydrometer an imperfect instrument without the
thermometer (1863)?

2. What quantity of water at 56° E. would be required to condense
1500 cubic feet of steam at a pressure of 35 lbs. per square inch above
the atmosphere, so that the temperature of the whole should be
100° E. (1865)?

176     STEAM.

Temperature of injection water is raised 100° - 56° = 44°F. = 24°4/9 C.
100°F. = 37° 7/9C, and temperature at 50 lbs. pressure = 282°F.
Total heat in steam at 282° F. = 1082 + .305 x 282° = 1168° F. = 649°C.
Relative volume at 35 lbs. above the atmosphere, or at 50 lbs., is
= 552.

The relative volume may be taken as the number of cubic feet of
steam produced from a cubic foot of water.

... Number of feet of water = 1500/532 = 2.71.

The steam has to give up 649 - 37 7/9 = 611°2/9C.
Since each unit gives up 24°4/9 C.

... Injection water required = 611 2/9 / 24 4/9 = 25 times the water evaporated.
... Quantity of water required = 27.1 x 25 = 67.75 cubic feet.

3. When a boiler is filled with sea-water, it is the practice to test
the degree of saltness from time to time; why is this? Describe the
apparatus employed, and the method of using it (1871).

4. Describe Giffard's injector, and give some explanation of its
action (Honours, 1871).

5. Describe the feed pump and valves necessary for supplying the
boiler of a locomotive. What is the principle of Giffard's injector
(1869)?

6. The brine pump of a boiler being choked, how is the brine to be
got rid of, the steam gauge indicating 4 lbs. and the upper surface of
the water being 2 feet below the level of the sea (1868)?

Ans. There will be nearly 1 lb. pressure per square inch to clear it.

7. Describe a method of ascertaining the degree of saltness of the
water in a marine boiler (1870).

8. How is the degree of saltness of the water in a marine boiler
ascertained ?

9. Show generally how to determine the amount of fuel lost by
the process of blowing out in marine boilers (Honours, 1871). See
questions at the end.

10. Give an analysis of sea water, and state clearly what is the
amount of solid matter in it.

11. How is the boiling point of salt water affected by the amount
of salt in it ?

12. Describe the manner in which the salt and impurities are
"blown off" from the surface.

13. What is How's salinometer? also state the principle on which
Seaward's salinometer is constructed.

14. What are the remedies against priming, and what do you mean
by priming? can you account for it taking place ?

15. Give the relation between fire-grate surface, heating surface,
and the evaporative power of the boiler in a marine engine.


Refs: Henry Evers, LL.D., Steam and the Steam Engine, London, William Collins, Sons, and Company, 1873. Chapter X, pp161-175.

 

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