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Yarrow torpedo boats. (Scale 1 : 12.) Made by the
Admiralty, 1889. N. 1830.

In this arrangement an air-tight flat is worked along each side of the
boiler at its central line, leaving the underneath part of the boiler clear
throughout its entire length. From this flat there are worked over the top
of the boiler two screens fitted with non-return air-flaps which open outwards
from the stokehold.

When under way the ash-pit doors, which are used only for the removal
of ashes, are bolted up, and the air, forced into the stokehold by blowing
fans, passes along through the air passages and non-return flaps to the
forward end of the boiler, and thence returns underneath to the furnace.
Should any accident occur to the boiler, the flaps close, and prevent steam
or flame from entering the stokehold.

u 2



308

913. Sectional model of Howden's arrangements for forced
draught. (Scale 1 : 24.) Made by the Admiralty, 1889.

N. 1828,

This arrangement, patented by Mr. J. Howden in 1883, belongs to the
" closed ash-pit " type ; the chief feature of the system is, however, the
provision made for warming the air before it is admitted to the furnaces.

To the front of the boiler an air-tight jacket is secured, into which
the air from the fans is delivered. This jacket is made of light iron plate,
and it extends over the front from some distance above the upper row of
tubes downwards, so as to enclose the furnaces and ash-pits. Immediately
above the smoke boxes are tubes through which the gases pass on their
way to the funnel ; while the hot gases pass through the inside of these
tubes, the air from the fan sweeps round amongst them, and recovers a
considerable portion of the heat that would otherwise be lost.

The smoke-box of each stack of tubes is completely separated from the
air chamber by casings, as are the furnaces and ash-pits, so that no air can
enter the ash-pits and furnaces except through the passages regulated from
the outside by valves. On the front of the casings referred to the outer
furnace doors and the ash-pit doors are hinged, while attached to the outer
furnace doors are the inner and true doors of the furnaces, which shut on
the front plate in the usual manner.

A dead plate, between the outer and inner front plates, separates the
ash-pits from the furnaces above the fire-bars, and into the space between
the dead plate and the inner and outer furnace doors, air is admitted in the
desired quantity through simple plate valves. After passing through the
perforations in the doors, at the sides and above the doors, the air is
received into cast-iron boxes, which serve the double purpose of protecting
the front plate and furnace doors, and distributing the air. When a furnace
or ash-pit door is opened for stoking purposes, the air valves for that
furnace close.

One of the early tests of this system was made in 1884, with the
S.S. "New York City," an iron cargo steamer of 3,700 tons displacement.
The engines were two-stage expansion, with cylinders 33 in. and 61 in. diam.
by 33 in. stroke. The original natural draught boiler had 2,173 sq. ft. of
heating surface and 75 sq. ft. of grate area. This was replaced by a boiler
with 1,310 sq. ft. of heating surface and 36 sq. ft. of grate area, fitted with
this system of forced draught. It was found that, while the earlier boiler
consumed 13 '5 tons of fuel in 24 hours when indicating 564 h.p., the new
boiler consumed 9 5 tons for 623 h.p.

Drawings of the boilers of S.S. " City of Dundee," fitted with this system
of forced draught, are shown in No. 858.

914. Drawing of Ferrando's arrangements for forced draught.
(Scale 1 : 8.) Lent by Messrs. Scott Bros., 1886. N. 1669.

This arrangement was patented in 1884 by Mr. J. Fernando, and has
been somewhat extensively adopted in cargo steamers on account of its
permitting the use of the cheap, small coal known as " duff."

In attempting to bum coal dust in an ordinary furnace, it was found
that the fire-bars had to be so very close together that the slag soon choked
the air passages, while if forced draught was resorted to, it carried off
unconsumed up the chimney a considerable portion of the fuel. The slag
difficulty was reduced by the use of grate bars of considerable depth, lying
close together and dipping partly in water, whereby the temperature was
kept sufficiently low to prevent the slag from adhering.

Mr. Ferrando's furnace was introduced to avoid the loss through the dust
being blown away unconsumed; for this purpose he arranged his fire-bars,
which were '19 in. apart, transversely to the furnace, whereby the coal
particles blown up remained longer over the glowing fuel, and so might get
consumed. The air is supplied by a blower, and is delivered into the closed
ash-pit, from whence it passes in a somewhat heated condition to the grate,
upon which even the poorest fuel has been successfully burnt.



309

On the S.S. " Calanae," a vessel of 1,586 tons register, fitted with
two-stage expansion engines, supplied with steam at 80 Ib. pressure, it was
considered that 337 tons of " duff " costing 51Z., with this arrangement did
the same voyage as 400 tons of coal costing 140Z., when burnt in open
furnaces.

915. Sectional model of the forced draught arrangements of
H.M.S. " Mersey." (Scale 1 : 24.) Made by the Admiralty,
1889. N. 1824.

The "Mersey" is a second-class cruiser, built at Chatham in 1885.
Her dimensions are : Displacement, 4,050 tons ; length, 300 ft. ; beam,
46 ft ; draught, 18 ft. She is propelled by twin screws, driven by
horizontal two-stage expansion engines, indicating 6,000 h.p., and giving a
speed of 18 knots. Steam at 110 Ib. pressure is supplied by six cylindrical
boilers, arranged in two stokeholds. The six boilers give a total of
18 furnaces, 399 sq. ft. of grate area, 11,700 sq. ft. of heating surface, and
weigh with water, uptakes, funnel, &c., 306 tons.

In the closed stokehpld system all openings into the stokehold are
closed by air-tight doors, except the inlets from the fans and the outlets
through the fires to the funnel. Communication between the boiler rooms
and the engine room on the deck is obtained by means of a passage at one
side, in which are air-locks, or pairs of air-tight doors, only one of which is
opened at a time. By their aid the pressure in the stokehold can be
maintained, in the same way as the gates of a canal lock retain the upper
water.

The model shows the boiler fronts projecting through a vertical air-tight
screen, worked from the bearers up to the ceiling, and dividing the boiler-
room, so that only a comparatively small space in front of the boilers is
under pressure.

The supply of air is collected above the deck, by means of cowl pipes
which terminate at the ceiling of the stokehold. There are two cowl pipes
to each stokehold, and at the foot of each pipe is a 5 -ft. fan for forcing the
air into the stokehold. As the air supply for both natural ventilation and
forced draught is brought through the same cowl pipes, provision is made
by means of doors for feeding the fans when in use, and stopping the
natural air supply. When the boilers are under forced draught the doors A
and B are open and C is closed ; when under natural ventilation the doors
A and B are closed and C is open. When under natural draught, the doors
in the passage and air casings are also opened.

The average indicated h.p. developed during the trial was 6,628, with an
air pressure in the stokeholds equal to 2 in. of water. This represents 16 61
indicated h.p. per sq. ft. of fire grate, and 21 7 indicated h.p. per ton of
boiler ; the coal used per indicated h.p. was 2 48 Ib. In ships of the time,
with natural draught, about 10 5 indicated h.p. was developed per sq. ft. of
fire grate, but with moderately forced draught between 16 and 17 indicated
li.p. were obtained. Taking the weight of the boilers as a basis, the effect
of the application of forced draught was to increase the power obtained
from a given weight in the proportion of 3 : 5 under similar conditions.

916, Sectional model of the forced draught arrangements of
H.M.S. " Trafalgar." (Scale 1 : 24.) Made by the Admiralty,
1889. N. 1827.

The " Trafalgar" is a sea-going turret ship, built at Portsmouth in 1887.
Her dimensions are : Displacement, 11,940 tons ; length, 345 ft. ; beam,
73ft.; draught, 27 - 5 ft. She is propelled by twin screws, driven by
three-stage expansion engines indicating 12,000 h.p., and giving a speed
of 16*5 knots. Steam at 135 Ib. pressure is supplied by six cylindrical
boilers arranged in two stokeholds. There are 24 furnaces, and the total
grate area is 659 sq. ft., the heating surface 18,300 sq. ft., while the total
weight of the boilers, &c., is 501 tons.



310

The engine and boiler rooms are divided at the middle line of the ship
by a watertight passage, 10 5 ft. wide, the upper part of which affords
communication between the ends of the ship, and is used for the transfer of
ammunition.

The model shows one stokehold of the " Trafalgar," with its three
single-ended boilers placed with their backs to the central tunnel. As in
the " Mersey" (see No. 915), the forced draught is supplied from a closed
stokehold system, but since the " Trafalgar's " boilers have return flues, a.
somewhat different arrangement is adopted. In addition to the vertical
screen, an air-tight casing is constructed in front of the smoke-boxes, and
along the ceiling and bulkheads hinged doors are fitted which can be
closed when working under air pressure. Communication with the stoke-
hold is made through air-locks. The air is forced into each stokehold by
three fans.

In the model, one boiler has the casing and smoke-box removed to show
the boiler front ; another has part of the forced draught casing removed to*
show the ordinary air-casing within ; the third shows the air-tight casing
for the forced draught, complete, with the exception of the doors, which
have been omitted to show the smoke-box.

During the trial the indicated h.p. developed under natural draught
was 8,520, with an air-pressure of 5 in. ; under forced draught 12,822
indicated h.p. was developed, with an air-pressure of 2-1 in. This
represents 19*4 indicated h.p. per sq. ft. of fire-grate, and 25 '5 indicated
h.p. per ton of boiler, under forced draught ; against 12 9 indicated h.p.
per sq. ft. of fire grate, and 17 indicated h.p. per ton of boiler, under natural
draught.

917. Sectional model of Martin's arrangements for assisted
draught. (Scale 1 : 24.) Made by the Admiralty, 1889.

N. 1825.

To avoid the inconvenience resulting from the use of a closed ash-pit
or stokehold, while retaining the increased rate of combustion due to>
mechanically assisted draught, Mr. W. A. Martin in 1885 introduced his
induced draught system. In his arrangement the fans, instead of blowing-
into the furnaces, are employed in withdrawing the gases from the smoke-
boxes or uptake, and then delivering them into the funnel.

The model shows, in section, a vessel with a three-furnace boiler, placed
fore-and-aft and flanked by coal bunkers. At the base of the funnel two-
fans are placed, one on each side of the uptake, and mounted on a shaft
carried through the uptake. A damper is fitted by which the passage of the
products of combustion may be regulated, or the course altered to that for
natural draught. As the fans have to work upon gases at a high tempera-
ture, their shafts are fitted with hollow couplings, by which the transfer of
heat along the shaft is so checked that the temperature at the journals is
kept within safe limits.

In 1890 a series of experiments upon Mr. Mai-tin's system of artificial
draught was carried out at Portsmouth Dockyard. The boiler so fitted was
of the locomotive type, and originally belonged to H.M.S. " Polyphemus ""
(1881). It had two furnaces, divided by a water partition ; the total grate
area was 20*7 sq. ft., and the total effective heating surface 758 sq. ft. lit
the final test, which lasted for 96 hours, with intervals for cleaning fires,
steam was maintained at a pressure of 75 Ib. ; the coal consumed was
39-87 Ib., and the water evaporated 389 '6 Ib. per sq. ft. of grate per hour.



918. Model of the " Farnley " corrugated flue. (Scale 1 : 16.)
Lent by the Farnley Iron Co., 1887. N. 1713.

This illustrates the' furnace flue patented by Mr. H. P. Fenby in 1885,.
and brought out by the Farnley Co. The resistance to an external
collapsing pressure is obtained by corrugations, which, however, run round
the flue at an angle of about 45 deg., forming helical grooves.



311

It is claimed for this form of corrugation that it not only stiffens the
tube, but also renders it a valuable stay for the ends of the boiler, sinco when
under pressure it tends to shorten ; in one case, under a pressure of 200 Ib.
per sq. in., some flues 42 in. diam. by 7 25 ft. long, shortened 031 in., and
returned to their original length on the pressure being relieved.

919. Model and drawing of the " Purves " ribbed flue. (Scale
1 : 24.) Presented by Messrs. John Brown & Co., 1889.

N. 1833.

This construction of stiffened furnace flue was patented by Mr. D. Purves
in 1885. By special machinery the tube is rolled with projecting rings at a
pitch of 9 in., the intermediate portions of the tube being left cylindrical and
thinner than the metal in the ribs.

The adjacent drawing, together with a section cut from an actual tube,
give some further information not obtainable from the model. Like the
Fox and Famley corrugated tubes, the Purves construction is designed to
strengthen cylindrical flues without introducing riveted joints.

920. " Serve " boiler tubes. Presented by Messrs. John
Brown & Co., Ltd., 1904. N. 2353.

These boiler tubes, patented in 1885 by Mons. J. P. Serve, are provided
with internal longitudinal ribs or fins which increase the surface for the
absorption of heat from the furnace gases into the surrounding water ; some
experiments with ribbed and plain tubes of the same diam. and length
showed that the ribbed tubes increased the amount of water evaporated
per Ib. of coal by about 15 per cent. It is also claimed that a boiler of given
power fitted with " Serve " tubes is lighter than a similar boiler with plain
tubes, a smaller number of the ribbed tubes of larger diam. providing the
requisite heating surface and flue area. The ribs are cut away for some
inches at each end of the tubes, to allow of their being expanded into the
tube plates.

The specimens show different stages in the process of manufacture, which
consists in preparing, by rolling, a plate of the required width and thickness
having the necessary ribs projecting from its surface ; this plate is then bent
to cylindrical shape and a la,p- welded joint formed, either by passing the
tube between welding rolls or under a powerful hammer, while a suitably
shaped mandrel is within it.

The tubes are made of mild steel, and for marine boilers, in which they
are largely used, the sizes range from 3 '25 in. to 4*5 in. in external diam. ;.
the specimens shown are 3 -25 in. diam., '125 in. thick, and have eight ribs
projecting '625 in.

921. Model of smoke-box door. (Scale 1 : 4.) Lent by the
Airtight Smoke Box Door Syndicate, Ltd., 1905. N. 2388.

This door was patented by Mr. J. H. Silley in 1903, and was designed to
provide means of quickly opening and closing smoke- box or furnace doors
whilst preserving an air-tight joint when shut.

Along each side of the door to be fastened is a stiff angle iron turning in
brackets on the door and capable of sliding in the direction of its axis.
Mounted on this angle iron is a series of wedge fasteners with inclined faces
to engage in a corresponding number of hooks or catches on the casing.
"When the door is fastened and is to be opened, the angle is slid up in its
bearings in an axial direction until it disengages the inclined faces of the
wedges from the hooks on the casing ; it is then turned about on its axis so
as to clear the catches and allow the door to open. By carrying the angle
the whole length of the door an intimate contact between the door and the
casing is obtained in the closed position, an air-tight joint thus being
secured.

It is stated that this form of door prevents buckling when subjected to
high temperature and air pressure, and thus keeps the door in working
condition.



312

922. Model of boltless furnace front. (Scale about 1 : 4.)
Presented by T. Downie, Esq., 1910. N. 2558.

This construction of furnace front was patented by Messrs. T. Downie
and D. Brown in 1906. It is designed to enable any of the removable parts
of the flame plate, or the door frame to be replaced quickly and simply
without the use of tools, as no bolts are employed.

The flame plate is in three parts, the upper piece having a projecting lug
or cotter cast on it. The lug passes through the furnace front and is
engaged and held in position by the upper part of the door frame. The two
lower side portions of the flame plate are held in position by the upper
portion, whose inner edges hold them in position. Each side portion is also
held at its lower edge by a lug on the dead- plate. The door frame slides
vertically into position and is held by four lugs, two at each side.

In the example shown the furnace front itself is in halves ; this con-
struction is for fronts of steel plate, and is intended to obviate failure due
to unequal expansion and contraction.

Furnace fronts of this construction are being fitted to the White Star
liners " Olympic" and "Titanic."



923. Model of telescopic funnel. (Scale 1 : 12.) Contributed
by Messrs. Jackson and Watkins, 1861. N. 542.

When vessels used their steam machinery chiefly as an auxiliary power
for employment only in exceptional cases, it was customary to provide means
by which the funnel could be stowed away so as to reduce the air resistance.
Small funnels were sometimes arranged to turn back, as on our river steam-
boats that pass under bridges, but for larger examples some form of
telescopic funnel was generally adopted.

The arrangement shown has only two telescopic lengths. The elevating is
done by two winches driven simultaneously by powerful worm gearing. It
resembles to some extent a device fitted by Messrs. Seaward and Capel
to H.M.S. " Sidon " in 1846, which appears to have somewhat anticipated
Taplin's design, subsequently so extensively adopted.

924. Model of telescopic funnel. (Scale 1 : 12.) Lent by
R. Taplin, Esq., 1857. N. 40.

The model shows an arrangement, designed by Mr. Taplin, of Woolwich
Dockyard, in 1848, which was awarded a medal at the 1851 Exhibition. It
was tried on H.M.S. " Hydra," and was subsequently adopted on nearly all
vessels in the Royal Navy, and to some extent in the mercantile marine.

The funnel is made in four lengths, the bottom one being fixed below the
decK level, and the other three telescoping within it ; each length is lifted
simultaneously by chains passing over pulleys 011 the top of the length below.
The chains of the lowest length are led to winch barrels, rotated by hand-
worked worm gear in the ratio of 1 : 36. The waste steam pipe has also a
telescopic length sliding in a simple stuffing-box, and is drawn up by the
second length of the funnel.

925. Model of telescopic funnel. (Scale 1 : 12.) Presented
by H.M. Commissioners of Patents, 1859. N. 543.

In this arrangement there is only one telescopic length, raised by blocks
and wire rope tackle, from a stout wire rope stretched from the crosstrees of
the adjacent masts. The hoisting winches are fixed to the masts, and have
a ratchet and pawl to prevent running back ; when the sliding length is up
it is further secured by four hinges and pins.



313

926. Salinometer. Contributed by W. Smith, Esq., 1866.

N. 1091.

Where boilers are fed with sea-water, it becomes a matter of great
importance to ascertain the degree of saltness of the water, since after this
has reached a certain density, the salts become precipitated as an incrustation
on the sides and tubes of the boiler.

The instrument shown was patented by Mr. A. P. How in 1849, and
measures the amount of salt present by indicating simultaneously the
specific gravity and the temperature of the solution.

The apparatus is combined with the water-gauge fittings of a boiler, and
consists of a gun-metal vessel which, by suitable cocks, can be filled from
the boiler and emptied as required. The top of the chamber is provided with
two openings, one for holding a thermometer, the other being fitted with a
perforated lining for holding a float by which the specific gravity of the
water is noted while at the same time the thermometer records the tempera-
ture. On the front of the vessel is a short table of temperatures and
densities.

927. Salinometer. Lent by T. 0. Buss, Esq., 1874. N. 1374. '

This is a form of hydrometer of variable immersion, specially constructed
and graduated for determining the density of water drawn from a steam
boiler. It, is made in German silver in the form of two cones with bases
together, and a vertical stem which is graduated downwards in steps. It
floats at zero in distilled water or at -^ in sea water ; -^ i g the maximum
reading that the water in a marine boiler is allowed to attain. A quantity
of water is drawn off in a suitable can for each test, and when it has cooled
to 200 deg. F. (93 -3 deg. C.) the reading is taken.

928. Salinometer. Contributed by George Nasmyth, Esq.,
1858. N. 216.

This instrument, which was patented by Messrs. F. Gr. Spray and Gr. Nevett
in 1849, registers the amount of salt present in the water within a boiler by
indicating the temperature ab which the solution boils under atmospheric
pressure.

The apparatus consists of a gun- metal globe connected to the boiler
front by a cock and having an outlet below, while projecting above the globe
is the stem of a thermometer. By opening the connection with the boiler
the water to be tested flows through the gun- metal casing until a steady
temperature is obtained which is that of the solution at atmospheric pressure
and the thermometer is graduated to read off the amount of salt in the
solution. Normal sea water containing about one part in thirty-two boils at
213 -2 deg. F.



929. Water circulator. Lent by Messrs. G. and J. Weir, 1890.

N. 1835.

This apparatus, called a " hydrokineter," is for promoting circulation in
boilers while steam is being raised. It consists of a series of nozzles placed
in line as in an injector. Steam from an auxiliary boiler is passed as a jet
through the central nozzle, drawing in and heating some of the surrounding
water, which it delivers at a high velocity in the direction in which the
circulation is defective. By this means the temperature of the water in the
boiler is equalised, and so steam can be rapidly raised without causing
any severe strains through unequal expansion of the various portions of the
boiler.



314

930. Asbestos-packed cocks for boiler fittings. Lent by
Messrs. J. Dewrance & Co., 1830. N. 2507.

Three forms are shown, but the special feature is the same in each, and
consists in the introduction of fibrous asbestos packing to secure tightness.
The plug is of the usual construction, but has comparatively little taper,
and the key is fitted to the smaller end. The body of the valve is formed
with four longitudinal recesses and a circular recess at each end, all to
be packed with asbestos. Above and below the plug are screwed covers,
which act as glands for tightening \ip the asbestos packing as required.
It is stated that such fittings permanently retain their tightness, and
are less liable to set fast than those of the simple metal on metal
construction.



931. Model of feed water regulator. (Scale 1 : 2.) Made
by Messrs. Henry Watson and Sons, 1899. N. 2205.

This apparatus was introduced to automatically control the feed water in
water-tube boilers, in which, owing to the small water capacity and great
rate of evaporation, the water level is subject to excessive fluctuations. It
was patented in 1895 by Mr. Alfred Blechynden and was first fitted in the
Royal Navy on the " Blechynden " boilers of H.M.S. " Pactolus."

The complete apparatus is placed in the separating drum at the top of
the boiler, and is controlled by a float enclosed in a perforated screen which
damps out temporary changes of level due to commotion in the surrounding
water ; the lever of this float is connected by a short arm to the regulator
shown, by which the feed water is admitted.

The float lever actuates a partially balanced double -beat valve, the
seating s for which are formed in a sleeve, adjustable longitudinally by an



Online LibraryScience Museum (Great Britain)Catalogue of the naval and marine engineering collection in the ... museum .. → online text (page 44 of 58)