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balance weights, is in one piece. The three main bearings are carried in
a cast-iron bed-plate, from which the cylinders are supported by three
vertical steel columns at the back and two raking ones at the front. The



282

rear columns are braced together and carry the guides, which are formed
of single rectangular bars, each being enclosed by its crosshead which
is forged solid with the piston-rod. The guide bars are independently
adjustable to insure accurate alignment, and the crosshead surfaces are
also adjustable for wear.

The steam is distributed through both the high and low pressure
cylinders by a development of the radial valve gear introduced by Hack-
worth, in which a single eccentric for each cylinder is employed and the
reversing and linking-up are performed by altering the position of the
centre of a suspended lever ; both gears are simultaneously altered by
a shafb at the back of the engine controlled by a simple reversing lever.
The adoption of this valve gear is facilitated by inclining the direction of the
valve rods so that they are not parallel with the piston-rod.

Lubricant is distributed from a large oil vessel at the back of the cylinder
by copper pipes leading to the various bearing surfaces, but in some positions
independent lubricators are provided.

This set of engines is designed for working with a boiler pressure of 150 lb.
per sq. in. and to run at 480 revs, per min., when it is capable of developing
about 30 h.p.

863. Launch engine (working). Presented by M. E. Rowe,
Esq., 1910. N. 2556.

This engine is of the four- stage expansion condensing type, with the
cylinders arranged in tandem pairs, the high pressure and the first inter-
mediate over the forward crank, and the second intermediate and low-
pressure over the after one. The cylinders are 3 in., 4 in., 5 25 in., and
7 in. diam. respectively, by 4 in. stroke. The crank-shaft, with its balance
weights, is of Siemens mild steel in one piece. As is usual in quick-running
engines of this type the framing is of a light and open character, and con-
sists of steel columns in the front and a cast-iron frame at the back, bolted
to a cast-iron bed plate ; the guides are formed in the back standard. The
slide valves are placed outside the cylinders in order to be easily accessible.
Reversing is effected by link motion of the Stephenson type. Steam is
distributed to the high-pressure and first intermediate cylinders by a single
slide valve having a large port at the upper end of sufficient width to serve
for both ports of the high-pressure cylinder, so that the steam exhausting
from the high-pressure cylinder at the termination of each stroke of the
pistons, passes through this port to the first intermediate cylinder. Steam
exhausting from this cylinder passes through the pipe at the back of
the cylinders to the valve -chest of the second intermediate cylinder. A
valve of similar construction serves for the second intermediate and low-
pressure cylinders, and is shown separated from the engine. This type of
valve was patented by Mr. G. Kingdon and Messrs. Simpson, Strickland &
Co. in 1897, together with a method of dispensing with a stuffing-box
in the partition plate between each pair of cylinders. The rods of the two
upper pistons have annular grooves cut in them, leaving a number of collars
on the rods, which fit the hole in the partition plate and form a steanitight
joint without the aid of a stuffing-box. Both the feed and air pump are
driven direct from the engine crossheads and have metal valves.

In conjunction with the water-tube boiler using liquid fuel (see No. 909),
this type of engine has been very successful. It occupies little fore-and-aft
space, but, on account of the imperfect nature of the balancing possible with
a two-crank engine, it is not so well adapted to high-speed running as a
three-stage expansion engine.

The engine shown is designed for working with a boiler pressure of
175 Ib. per sq. in., and is capable of developing 14 indicated h.p.

864. Petrol launch engine with reversing gear. Lent by the
Wolseley Tool and Motor Car Co., Ltd., and Messrs. Hesse
and Savory, Ltd, 1911. N. 2594.

The engine shown is a high-speed petrol motor working on the Otto
cycle ; it has mechanically operated valves and electric ignition. The four



283

cylinders with their jackets, and the top part of the crank case, including
the combustion chamber heads, are cast en bloc. The lower part of the
crank case, which is of aluminium, contains the crank-shaft bearings, and
has four arms for bolting the whole to the engine bearers. The water
circulation is effected by a pump driven by enclosed gear off the crank-shaft.
The exhaust pipe, which is connected with a silencer (not shown), is cast on
the cylinders ; this pipe, together with all passages and cylinder walls in
contact with the hot gases, is water cooled.

Lubrication is carried out by means of a rotary pump driven off the cam-
shaft. The oil is delivered to narrow troughs under each connecting rod
and the big ends are fitted with scoops which dip into the troughs at every
revolution, keeping up a continuous splash on the gudgeon-phis and pistons.
The level of the oil in the troughs is kept constant by means of the pump,
the pressure of oil in the system being registered by a gauge. All oil is
filtered before being distributed.

A cam-shaft, driven from the crank- shaft by enclosed gearing at half its-
speed, operates the inlet and exhaust valves by means of rockers formed
solid with the shaft; the valves are returned by springs. Access to any
valve is readily obtained by removing its cap.

The carburetter, where the explosive mixture is prepared, is of the float-
feed spray type. A cylindrical chamber in which petrol, fed by gravitation
or a feed pump, is maintained at a constant height by a needle valve actuated
by a float, is connected with the mixing vessel. In order that the richness
of the mixture of petrol and air can be regulated, a flat valve controlled by a
spring governs the admission of air. When running at high speeds more
air is admitted owing to the increased air- suction causing a greater depression
and consequent opening of the valve. A throttle valve, controlled by hand,
regulates the supply of the explosive mixture. In addition to the main jet,
a small supplementary jet is provided to facilitate starting. This jet com-
municates with a small-bore suction pipe which passes direct to the main
induction pipe, and is unaffected by the position of the throttle. The mixing
chamber is heated by being jacketed with the exhaust gases, a small pipe
being led from the main exhaust for this purpose.

High tension ignition on the Bosch system is employed, and the time of
ignition can be varied. Starting is effected by means of a handle and
completely enclosed chain, fitted at the forward end of the motor ; the chain
can be tightened without removing the cover.

The combined clutch and reversing gear is of the type patented in 1905-8
by Mr. G. Savory. It is compactly enclosed in a light welded sheet steel
case, the clutches and bevel gear running in an oil bath. Upon the end of
the crank- shaft is a keyed cone clutch the motor clutch. For ahead
driving, this clutch engages with an inner clutch keyed to the propeller
shaft. This drive is direct, and the reversing bevel gear is idle. Embracing
the motor clutch is a third or astern clutch, which is fixed to one member
of the reversing mechanism. The latter reverses the bevel wheel driving
the dog clutch on the propeller, shaft. The total travel of the propeller
shaft and propeller for engaging ahead or astern respectively is only
1 375 in. An important feature of the design in this gear is that the pro-
peller thrust tends to keep the ahead clutch in engagement with the motor
clutch when running ahead, and the propeller pull acts similarly on the
astern clutch when running astern. A hand-operated lever gives ahead,
astern, or neutral positions in the 12 h.p. example shown ; in large sizes of
the gear a wheel is substituted for the lever. At the motor or forward end
of the gear is fitted a thrust block, the lubrication of which is ensured by
needle oil- ways between the collars and the oil receptacles into which the
thrust collars dip.

The four cylinders are each of 3 -125 in. diam. by 4-5 in., stroke develop-
ing 13 brake h.p. when running at 1 ,000 revs, per min. The total weight of
the engine without the fly-wheel is approximately 300 Ib.



284

865. Model of torpedo boat engine. (Scale about 1 : 24.)
Lent by R. L. Robinson, Esq., 1908. N. 2485.

The model shows the usual arrangement of a set of three- stage expansion
engines as fitted to small fast vessels such as torpedo boats and large yachts.
The introduction of wrought iron or steel pillars and diagonal bracing by
Sir J. I. Thornycroft in the engine framing of a river yacht has since found
universal application in small high-speed vessels. This light and open
framing is shown on the model.

Large bearing surfaces are usually provided in this type of engine in
order that it may be run at high speeds without excessive heating and
wear. The reversing gear which is controlled from the starting platform
by a large hand-wheel is of the usual shifting-link type. The air-pump is
driven from the low-pressure crosshead by rocking levers.

A single four-bladed propeller and the thrust block are shown.



866. Model of Parsons marine steam turbine. (Scale 1 : 24.)
Lent by the Parsons Marine Steam Turbine Co., Ltd.,
1908. Plate X., No. 5. N. 2487.

The model shows a typical three-shaft arrangement of marine steam
turbine as usually fitted to mercantile 'vessels and yachts. The arrangement
consists of one high-pressure turbine driving the centre shaft, and two low-
pressure turbines, working in parallel, driving the wing shafts; in the
exhaust casing of each of the low-pressure turbines is placed a reversing
turbine. When going ahead, steam from the boilers is admitted through
the main regulating valve to the high-pressure turbine by the two steam
pipes shown, and after expansion it passes to each of the low-pressure
turbines, and from them to the condensers in the wings of the ship. When
manoeuvring, the wing shafts only are used, steam being admitted by the
smaller valves shown on the bulkhead, directly into the low-pressure turbines
or into the reversing turbine as required. By this means the port or
starboard engine can be worked ahead or astern independently of each other
and of the high-pressure turbine, which rotates idly in a vacuum whilst the
vessel is manoeuvring.

In recent practice the rotor wheels are of cast steel, the spindles of
forged steel, the casings or outer cylinders of cast iron, and the blades of
hard drawn brass.

Thrust blocks are fitted at the forward ends of each of the spindles.
These are necessary because the steam thrust aft does not always balance
the propeller thrust forward. The former is usually in excess at full power,
and the latter at low power. The difference between these two thrusts is
transmitted by collars turned on the end of each rotor spindle. These act
on the top half of the thrust block when the steam thrust is in excess, and
on the bottom half when the propeller thrust is in excess. Independent
gear is provided for the top and bottom halves of the thrust block in order
to move the rotor for the adjustment of clearances.

Where the rotor spindles pass through the ends of the drums, glands
specially designed by Mr. Parsons are fitted. For the greater part of the
length of the gland radial fins extend alternately from the spindle and from
the casing into the annular space between. The action of these fins is
alternately to wire-draw and to expand the steam, thus reducing the steam
pressure as it travels outward. At the outer end are fitted four Bams bottom
rings, and the small amount of steam which is allowed to leak past them for
lubrication is conveyed by means of a pocket to the auxiliary condenser or
exhaust tank. In the event of the fins not sufficiently reducing the pressure
of the escaping steam, this pocket, in the high-pressure turbine, can be
connected with the low-pressure turbine at a point where the pressure is
just below the atmosphere. In the case of the low-pressure glands, air can
be prevented from leaking in by maintaining a pressure of from 2 to 3 Ib. per
fiq. in. in the pocket by means of a small steam pipe.



285

Provision is made for neutralising the steam pressure on the end of the-
rotor wheels by balancing it against a similar pressure on a balance piston
or dummy which is fitted at the forward end of each turbine inside the
casing, a similar astern dummy being fitted at the after end of the reversing
turbine. This balance piston has a steam-packed gland between it and the
turbine casing.

As the efficiency of a steam turbine depends largely on keeping the
leakage of steam at a minimum, great attention is paid to maintaining very
small clearances. Over the tips of the blades, this is effected by milling
them to a thin edge, so that if they accidentally touch the drum they will
grind clear. The ahead and astern dummies and the gland fins are tapered
away for a similar reason. The clearances can be measured directly by a
micrometer gauge fitted for the purpose.

Governor gear, operated by a worm on the rotor shaft, is fitted to each
of the turbines, and shuts off the supply of steam should the revolutions of
the turbines increase much above the normal speed. Special attention has
been paid to the lubrication of the main bearings and adjusting blocks in
this type of engine. Oil under pressure is delivered by steam pumps to the
bearings, after which it flows to a cooling tank fitted with copper coils
through which the water is circulated. After passing through oil filters it
is then re-delivered to the bearings. A complete water circulation is also
maintained through the bearings, which are made hollow for this purpose.

Lifting gear consisting of screws and worm gear driven by electric
motors is provided in the engine-room in order to facilitate the removal of
the upper halves of the turbine casings for inspection or repair.

Owing to the importance of a high vacuum, a special fitting called a
" vacuum auginenter " or " augmented condenser " has been introduced ; it
consists of a steam jet placed in a contracted pipe between the condenser
and the air pump. The jet draws the air and vapour from the condenser
and, in the contracted pipe, the mixture is compressed to about one-half of
its bulk. It is then delivered to the air pump through a small auxiliary
condenser, the condensed water gravitating directly from the condenser to
the air pump.

In the S.S. "Manxman" with this fitting, the vacuum, at low power
reached 29 in. with the barometer at 30 '2 in., the rise due to the auginenter
varying from 1 -25 in. to 1 '5 in., representing an additional economy of 7 to
8 per cent. Greater power is provided for by fitting a by-pass in the
high-pressure turbine which will admit steam directly to a lower set of
blades.

A sectional model of a portion of a Parsons steam turbine showing the
construction of the blading is exhibited in the Mechanical Engineering
Collection.



MARINE ENGINE DETAILS.

867. Photographs of engines of S.Yt. " Sareea," fitted with
Bremme's valve gear. Presented by Messrs. Ross and
Duncan, 1887. N. 1705.

The vessel is an Egyptian coastguard yacht, and is fitted with a two-
stage expansion surface condensing engine, having cylinders 10 in. and
20 in. diam. by 14 in. stroke. With a boiler pressure of 100 lb., 120 h.p.
was indicated at 200 revs, per min., and the speed attained was 9 55 knots.

The valve gear used is that patented in 1879 by Mr. G. A. C. Bremme,
of Liverpool, in which only a single eccentric is used, both linking up and
reversing being performed by moving the centre of a swinging lever that
controls the motion of the eccentric rod. Another photograph shows a small
three- stage expansion engine made for the Japanese Naval College at
Etajima, in which this valve gear is also employed.



286

The Bremme valve gear is identical in action with that invented and
introduced by Mr. J. W. Hackworth in 1859, which is described and shown
in motion in the Mechanical Engineering Collection.

868. Drawing of Stevart's valve gear. (Scale 1 : 10.) Pre-
pared from information contributed by Druitt Halpin, Esq.,
1903. N. 2326.

This modification of Walschaerts valve gear was introduced by Prof. A.
Stevart in 1868, and the drawing shows it as applied to some steamers plying
on the river Meuse. The arrangement is only applicable to engines having
two cylinders set at right angles and driving one crank-pin, or else two
cylinders in the same plane driving cranks at right angles.

The oscillation of the link of the usual Walschaerts gear, giving motion
to the valve equivalent to that from an eccentric with 90 deg. advance, is
liere obtained, for one engine, from the crosshead of the other, while the
lead for each is derived in the usual manner from its own crosshead ; the
result is that the motions for both valves are obtained without the use of
eccentrics or return cranks.

869. Photographs of marine engines fitted with Marshall's
valve-gear. Presented by F. C. Marshall, Esq., 1881.

N. 1550.

These show a pair of two-stage expansion horizontal engines for driving
twin screws. They were built by Messrs. B. and W. Hawthorn, of
Newcastle, with cylinders 30 in. and 60 in. diam., by 36 in. stroke ; with
steam at 90 Ib. pressure they made 55 revs, per min., and indicated
2,700 h.p.

The valve gear employed is that invented and introduced by Mr. Marshall
in 1879-80 : it is similar to that of Mr. J. "W. Hackworth, which is shown in
motion in the Mechanical Engineering Collection. The adjacent indicator
diagrams were obtained by Mr. Marshall in 1880 from the engines of
S.S. " Lord Jeffrey," which indicated 927 h.p.

870. Motion diagram of Joy's radial valve gear. Presented
by David Joy, Esq., 1900. N. 2087.

This reversing and variable expansion gear, introduced by Mr. Joy in
1880, has been very extensively adopted in both land and marine engines.
It dispenses with eccentrics, the motion for the valves being derived entirely
from the travel and swing of the engine connecting-rod.

The valve rod is connected to the short end of a long lever, the other
end of which is indirectly coupled to the engine connecting-rod. The
fulcrum of this lever is fitted with a block sliding in a curved guide, and the
engine is reversed or " linked up " by altering the angle that this guide
makes with the valve rod. The guide is shaped to a circular arc of a radius
equal to the length of the valve rod, and the block, when the engine is
running, works equally on both sides of the centre of this guide. The
sliding motion of the lever in the curved guide gives the equivalent to
90 deg. of angular advance in an ordinary eccentric gear, while the rocking
motion of this lever gives the lead. As the crank-shaft rotates, any point
on the connecting-rod has a nearly elliptical path, which would give an
unequal distribution of the steam at the two ends of the cylinder if the long
lever were directly attached to the connecting-rod. To avoid this objection
the motion is obtained from a link, one end of which is attached to the
connecting-rod and the other to a radius rod. A point in this link describes
an oval path, giving a symmetrical motion to the slide valve.

It is stated that, in mid-gear, steam is admitted into the cylinder to the
extent of the lead at each end, and that the lead is constant for all positions,
although unequal lead can be arranged for if preferred.

For the sliding block and a curved guide a swinging lever is sometimes
substituted, the inclination of the curved path so obtained being altered by



287

changing the position of the stationary end of the lever. An adjacent
photograph, of the engines of the Italian ironclads " Be Umberto " and
41 Sicilia," shows this arrangement.

In this diagram a simplification, by Mr. Joy, of the valve arrangements
for a three -cylinder marine engine is also represented. With each cylinder
acting on separate cranks set at 120 deg., cylinders Nbs. 1 and 3 each
has a complete gear, while the valve of No. 2 receives a corresponding
motion from the centre of a lever connecting the valve rods of Nos. 1 and 3,
without further mechanism. To facilitate the examination of this point,
the three cylinders in this motion diagram are shown displaced from their
true positions.

871. Drawings of Laing's valve gear. (Scale 1 : 16.) Pre-
sented by Andrew Laing, Esq., 1887. N. 1706.

The engines represented are a two- stage expansion set, with oscillating
cylinders 60 in. and 104 in. diam. by 7 ft. stroke, supplied with steam at
80 Ib. pressure, and indicating 4,000 h.p. Seven sets of these engines were
fitted to the paddle steamers of the Queenboro' and Flushing service.

The valves are worked by Laing's single eccentric gear. This is a radial
valve motion, in which the swinging of the cylinder gives the movement
equivalent to the 90 deg. advance of a simple eccentric ; the lead is given
by a single fixed eccentric arranged in a line with the crank. Reversal is
performed by altering the position of the fulcrum of the lever by which
these combined motions are transmitted to the valve. In Walschaerts
reversing gear (see No. 854), which also has only one eccentric, the two
duties are distributed in the opposite manner.

872. Motion diagrams of Joy's fluid pressure valve gear.
(Scale 1 : 6.) Presented by David Joy, Esq., 1900.

N. 2085-6.

This arrangement for altering the grade of expansion of an engine, or
for reversing it, was patented by Mr. Joy in 1892. The feature of the gear
consists in the use of a single eccentric which can be readily moved in a
straight path from the position for forward gear to that for backward. It is
shown fitted to a marine engine of 9,000 indicated h.p., with cylinders
33*5 in., 49 in., and 74 in. diam. by 39 in. stroke.

The eccentric is forced over by means of fluid pressure, acting upon
rams formed on the crank- shaft and working in cylinders fixed within the
eccentric sheave. The fluid is introduced to these cylinders through central
holes drilled along the crank- shaft, and by pipes connected with the fluid
distributing arrangement. This consists of two vertical cylinders with a
common piston rod, the upper cylinder being for steam, and the lower for
oil or other fluid supplying the pressure. Steam is admitted to either end
of the upper cylinder through a small slide valve worked by the hand lever,
and there is also a slide valve in the oil cylinder. The steam, admitted into
the upper cylinder moves the piston in the oil cylinder, and so, by the fluid
connection, moves the eccentric over to a corresponding extent.

If the oil leaks or an eccentric ram leather gives way, the eccentric goes
to full gear, forward or backward, according to the way that the engine is
running, and remains there.



873. Model of steam starting engine (working). (Scale 1:4.)
Made by Messrs. Brown Brothers & Co. Received 1903.
Plate XL, No. 1. N. 2335.

The original form of this arrangement for applying steam power to
move the reversing gear of a large steam engine was patented by Mr. A. B.
Brown in 1867. It differs from the " all-round " reversing gears in that



288

the steam pressure acts directly upon a piston connected with the reversing
shaft, instead of through a small rotative steam engine and worm gearing.

The appliance, which is usually attached to one of the standards of the
main engine as shown in the model, consists of a lower steam, or motive,
cylinder and an upper hydraulic, or control, cylinder ; their two pistons are
connected by a common piston-rod from which the power is transmitted to
the weigh, or reversing, shaft of the main engine by side links. The valve
of the steam cylinder and a by-pass valve of the hydraiilic cylinder are
connected by a common valve rod, so that when the steam valve is moved
from its mid position the by-pass is opened and allows the piston to move ;
when in the mid position, however, the pistons are held stationary owing to
the hydraulic by-pass being closed.

Reversal by this apparatus is effected by a small hand lever connected
to an intermediate point in a nearly horizontal floating lever, one end of
which is connected to the arm of the weigh- shaft and the other end to the
valve -rod. When the hand-lever is moved it moves the valves and thereby
causes a corresponding but greater movement to be made under steam



Online LibraryScience Museum (Great Britain)Catalogue of the naval and marine engineering collection in the ... museum .. → online text (page 40 of 58)