THE COLLIERY GUARDIAN

AND

JOURNAL OF THE COAL AND IRON TRADES.

Vol. CVIII.

FRIDAY, NOVEMBER 1.3, 1914.

No. 2811.

INDUSTRIAL LOCOMOTIVES.*

By J. W. HOBSON
(Continued from page 970-7

Tubes.

Although tubes are primarily for obtaining a large
heating surface, there is a tendency on the part of some
to get as many as possible crowded into a boiler, thereby
inviting endless trouble through the spaces between the
tubes themselves and between the tubes and the barrel
becoming choked with scale. Also the bridges in the
tube plates are too small and the tube holes are too
close to the flanges of the firebox tube plate, thus
causing cracks. The circulation is impaired and the
efficiency of the boiler reduced — a cushion of steam
being formed on the tube plate which cannot readily
make its escape when the tubes are too closely pitched,
and this, without doubt, is one of the causes of leaky
tubes. The water space between the tubes should be a
minimum of f in., which also allows for repeated expand-
ing. The most common arrangement of tubes is to
have them in vertical rows, which permits better circu-
lation, and allows sediment to fall to the barrel.

Tubes vary in size from 1| in. to 2^ in. outside dia-
meter, depending on the size of boiler, and it is cus-
tomary to have them in. larger in diameter at the
smokebox end to facilitate easy withdrawal. In the
case of owners having engines of various sizes, it is a
good plan to adopt a standard diameter of tube, so that
replace tubes can be kept in stock to suit all engines.
Locomotive boiler tubes are made from a variety of
materials, but by far the great majority are of solid
drawn brass.

Copper tubes are occasionally used for industrial
engines, though they are very expensive. They should
be just soft enough to stand expanding without the
ends splitting; if too soft they become badly scored by
the particles of unconsumed fuel, as at times the blast
is very severe. Experiments and practice prove that
there is little difference in the evaporative powers of
copper, brass, steel, or iron tubes after a few weeks
working with bad water; but in almost every case the
more expensive materials last very much longer, and
after use their scrap value is a consideration.

In order to obtain an initially cheaper engine, some
engineers have tried mild steel tubes, both hot and cold
solid drawn. Others again have experimented with
charcoal iron tubes, but steel and iron tubes deteriorate
very rapidly in the great majority of cases. There are,
of course, exceptions, so that it appears to be quite a
question of local conditions, viz., the quality of feed
water and fuel used. There is also a difficulty experi-
enced in keeping steel and iron tubes tight in the
copper tube plate unless fitted with copper ends, and
incrustations adhere more firmly than in the case of
copper or brass.

Taking all into account the general use of brass tubes
is justified. With ordinary working pressures these
should not be less than 12 i.w.g. thick at the firebox
end, tapering to 14 i.w.g. at the smokebox end, whilst
for steam raising purposes steel or iron tubes should
not be thicker than 11 or 12 i.w.g. owing to the diffi-
culty of the heat passing through to the water side.
Brass tubes are expanded in the tube plates, and gener-
ally ferruled at the firebox end only, though some engi-
neers prefer them beaded over at the firebox end in
addition to ferrules. In the case of plain steel and
iron tubes which are beaded over in the firebox tube
plate, ferrules are not required.

It is not generally known, and is worth noting, that
ferrules are not for the purpose of keeping tubes tight
(this being done by expanding), but are for protecting
the tube ends from the action of the fire.

* From a paper read before the North-East Coast Insti-
tution of Engineers and Shipbuilders.

Dome.

The reason of having a dome is primarily to collect
the steam as dry as possible. It also serves as a means
of admission to the boiler at a time of extensive repairs.
When it is not possible to have a dome, a steam collect-
ing pipe, perforated on the upper surface, is placed as
high as possible in the barrel, and the regulator is fitted
in the smokebox. Domes vary much in design, but the
most approved form for this class of engine is to have
the base pressed from a steel plate, the barrel rolled into
circular form and riveted with inner and outer butt
strips, and completed with a dished plate cover fixed
with studs to a weldless angle ring riveted to the dome
barrel. Some makers fit a welded dome, but a welded
joint depends entirely on the skill of the workmen, and
it is not easy to judge from appearances whether the
weld is sound or otherwise. Dome cover joints should
be faced and made with boiled oil, or a paste of black-
lead and boiled oil. This latter makes a capital joint,
which lasts well, and when opened up is as smooth as
when first made.

Washing Out Facilities.

The locomotive boiler being a powerful evaporator for
its size, it follows that it should be elaborately provided
with mud plugs, mud doors, etc., for cleansing purposes.
These should be distributed somewhat as follows :—At
least two. mud plugs in the smokebox tube plate above
the tubes, and a mud door or mud plug at the bottom
near to the barrel. One mud plug at each bottom corner
of the firebox, and a mud door front and back of the
firebox—all as near as possible to the foundation ring.
At least three mud plugs in the boiler back to enable
inspection and cleaning of the firebox top, and also one
plug or door on each corner of the firebox back about
on a line with the top of the firehole ring. When the
water used is very dirty, this number should be con-
siderably augmented. A manhole about 13 in. diameter
in the bottom of the boiler barrel in close proximity to
the throat plate is a great acquisition in giving easy
access to the boiler for inspection and repairs when the
tubes are removed. Failing this, a mud door about
5 in. diameter enables a ready examination of the palm
stays, as well as affording an exit for the scale when
cleaning the barrel.

The boiler should be cleaned out with regularity, the
intervals varying in different localities. Some kinds of
water are so good as to leave little or no deposit, other
kinds are so bad that if the cleaning out is neglected,
the heating surface becomes almost useless, and the
liability to damage by overheating is increased to a most
serious extent. When the boiler requires cleaning it
should be allowed to cool down before running the water
off, otherwise it will be strained by the sudden contrac-
tion, but if hot water at 80 to 1001b. pressure is procur-
able for this purpose, then delay is obviated and the
scale more readily removed. To ascertain as far as
possible that all scale has been removed, a small electric
light attached to a rod would be of considerable advan-
tage. Some precaution should be taken, especially in
the case of the firebox, where, if scale remained, local
overheating of the plates and leaky stays would result.

Regulator.

The regulator for controlling the supply of steam to
the cylinders is almost universally an iron casting having
two ports over which slides the main valve. This latter
is given an upward movement which uncovers the ports
in the regulator top. In the main valve there are two
narrow ports in direct communication with the ports in
the regulator casting. These small ports in the main
valve are first uncovered by an easing valve, which
slides over the main valve. This easing valve moves

prior to the main valve, thus somewhat equalising the
pressure on each side of the main valve, which then
becomes easy to control. It is advisable for the regu-
lator to be so arranged that it is opened by the valves
moving upwards, so that in the event of a pin shearing,
or any of the rods failing, there is a tendency for the
valves to close and thereby stop the engine.

Safety Valves.

The most common form of valve is that known as the
Ramsbottom type, and is usually an iron casting with
two columns standing vertically on a seating placed on
top of the firebox. The columns have gunmetal seats
and valves provided, the latter being of the wing type,
deeply coned to take the points of the holding down
lever. This lever is connected to a coil spring, which is
in turn secured to the safety valve base. Safety links
are attached to the lever in order to prevent it and the
valves from being carried away in the event of the spring
failing.

In some instances pop valves are fitted in place of
the above. These are certainly more sensitive, and give
a more rapid release. They also take up less vertical
height, which is a consideration when an engine has to
be constructed to take up little height.

Boildr Feed.

The feed water is supplied to the boiler by injectors,
two being fitted, each of which should be of sufficient
power to supply the boiler when working separately. The
injectors are either of the type known as combination,
and fitted on the boiler back, or the horizontal type,
fitted direct to the tank bottom. It is advisable to have
the former class fitted on engines with a large enough
boiler back, i.e., 16 in. engines and upwards, but it is
very difficult to arrange this type on smaller engines
without overcrowding the mountings, dispensing with
mud plugs, or obtaining satisfactory seatings. With
combination injectors, steam valves and clack boxes
are not required.

t Boiler Mountings.

These should consist of the following :—Two sets of
water gauges with protectors, steam blower valve, steam
brake valve, pressure gauge and cock, whistle and valve,
blow-off cock, and injector steam valves if combination
injectors are not fitted. It is customary and good prac-
tice to fit the injector steam valves and whistle cock
into a mounting on the firebox top usually termed a
steam stand. This latter should have a close down valve
provided so that the steam can be shut off in the event
of the steam valves, etc., requiring attention. Care
should be taken, however, tli'at the pressure gauge cock
is not included but is always in direct communication
with the boiler.

Smokebox.

This chamber forming the front end of the boiler, and
into which the waste gases and unconsumed particles of
fuel are emptied from the tubes, should be carefully
built up and made perfectly airtight, as it is therein
that the draught is created which makes the locomotive
boiler such a powerful evaporator. In addition to the
steam pipes being led to the cylinders through the
smokebox, this chamber naturally contains the exhaust
pipe. With regard to the latter, there have been from
time to time many experiments made with a view of
determining the correct size and height of the nozzle
of this important detail which induces the draught, but
so far nothing definite has been elucidated. The follow-
ing ratios taken from actual practice, in every instance
the engine doing good work, vary as follow :—

Average of
examples
taken.

Area of piston	_ 12*8	20’7	16*5

Area of nozzle, .......... 1	1	1

Volume of cylinder (cu. in.) _ 211	495	300

Area of nozzle (sq. in.)	1	1	1

Area of grate	_ 120	213	160*7

Area of nozzle ........... 1	1’1

The requisite size of nozzle depends upon a variety of
circumstances, other than the volume of cylinder and