1264

THE COLLIERY GUARDIAN.

June 5, 1914.

There are only a few makes of high-power vertical
engines, and those of tandem type are limited in size to
about 1,500-brake horse power. As some of these
engines have no less than 12 cylinders, we cannot look
for much further development in this direction. Owing
to the multiplicity of cylinders, and the enormous
number of valves, springs, cams, and operating
mechanism generally, the complication becomes ridi-
culous. The main object in the multiplicity of
cylinders has been to avoid the water cooling of pistons;
but, as the cooling of pistons has now been in use with
absolute reliability—even in connection with high-speed
engines for a number of years—it is hardly a wise policy
to construct an engine with 12 cylinders and 24 valves,
when an engine with four cylinders will perform the
same operation.

The single acting engine just mentioned has also
another defect, in that it is impossible to control with
any degree of certainty the supply of lubricating oil to
the cylinders. Where engines of high power are in
continuous service, lubricating oil becomes an item for
careful consideration—not only on account of its cost,
but owing to the frequent necessity for cleaning out the
cylinders. Isolated cases can be found where single
acting engines have run for some months without any
grinding-in of valves, or of stopping to clean out the
cylinders and pistons; but in the case of double acting
engines, where the supply of oil is entirely independent
of the splash in the crank chamber, engines have run
for periods of two years without any necessity to clean
the cylinders. This type of engine is therefore the one
to be adopted, if continuous service and reliability are
required. As previously stated, reliability must have
the first consideration, and the engine which is always
ready for service, and will develop its power for long
periods without stopping, is the one which will in the
end gain favour.

Gas Engine Defects.

The writer will now consider for a moment -what are
the weak points of gas engines, as it is of no use to
state that there are no weak points.

One of the weak points in connection with large single
acting vertical gas engines is the frequent necessity
for cleaning out the cylinders. So long as the pistons
are exposed to the underside of the crank case this diffi-
culty cannot be overcome efficiently, as there is no
means of controlling the amount of oil which passes up
from the crank chamber.

Another weak point is the burning and failure of the
exhaust valves, which require occasional cleaning and
grinding-in, and many failures are still experienced
because of breakage of valves. Another weakness is in the
ignition gear, although, generally speaking, it must be
admitted that failures from this cause are few and far
between, provided, of course, that a modern reliable gear
is fitted to the engine in the first instance. From the
available statistics one infers that the freedom from
breakdown in gas engines is very encouraging, and the
weaknesses just mentioned may be looked upon as the
only ones that are liable to cause occasional stoppage.

If the engines are made on steam engine lines, with
double acting two-cycle cylinders, the size of the work-
ing piston need be about only a quarter of that of the
four-cycle single acting type, and for the same power
the strains are proportionately less : both these points
are very advantageous in the case of large engines. In
the case of single acting engines the pistons are usually
called upon to serve as the crossheads; and, although
they appear to wear exceedingly well, this type will
doubtless in the near future be obsolete.

In steam engines of the high-speed forced lubrication
type with cross heads designed to take the thrust, and
motion work of substantial design, which can be lubri-
cated lavishly without any fear of clogging the cylinders
with oil, long continuous runs can be made with abso-
lute certainty. In these engines, which are of the
vertical type, the pistons are absolutely relieved of
pressure, and can be made as light as convenient; con-
sequently, they will remain a good fit, and be tight for
many years, even when they are in continuous service.

Mather and Platt Duplex Engine.

In fig. 1 is illustrated partly in section a line of parts
which represents—in the writer’s opinion—the type of
engine that must ultimately supersede all others for
high power. This engine will no doubt be recognised
as one made by Messrs. Mather and Platt Limited.
What the writer wishes to imply is that the double
acting two-cycle engine—-built on substantial lines as
represented—-and which long experience in steam engine
practice has proved so successful, will be the one that
will ultimately be used by all large vertical engine
builders. While considering the tendency towards sim-
plicity, it might be mentioned that the engine just
referred to is without valves altogether to the working
cylinders; consequently it possesses great advantages
in the direction of reliability for continuous work. As
the engines are built on the two-cycle principle, separate
air and gas pumps are required, but these are driven
directly from the crank shaft; their valves also -are
operated directly from the crank shaft in a manner
similar to those of high-speed steam engines. Owing
to this fact, no gears, cam shafts, tappets, or springs are
required, and the engine operates as silently as the well-
known high-speed steam engine.

Accessibility is of prime importance, and in modern
engines this point has received most careful considera-
tion. Even in vertical tandem engines we are informed
that it is possible to open up and get at the lower piston
within 40 minutes on a 1,000-horse power engine. This
speaks very well for the design. For long continuous
work it is also of great importance that the bearing and
working surfaces should be liberal, and the strength of
the parts most carefully proportioned to resist the work
which they are called upon to bear. In the type of
engine illustrated, the only working parts are the main
motion work, which is of ample proportion, and so

arranged that it can be well lubricated without waste of
oil, the crank chamber being entirely separated from the
working cylinders by means of a distance piece.
Scraper glands are fitted at the top of the crank
chamber, as is the usual practice in high-speed steam
engines. The oil is thus effectually prevented from
being carried up into the working cylinders even by
means of the piston rods.

The working cylinders are lubricated by mechanically
driven lubricators, having a separate pump to each feed,
and the supply of oil is thus reduced to a minimum. By

Fig. 1.—Vertical Double-acting Gas-engine.

this accurate system of lubrication for the cylinders it
is possible to run the engines over exceedingly long
periods without cleaning or any fear of their becoming
clogged up with oil, and this is a great advantage for
continuous work. As the pistons and piston rods are
water cooled, this does away with the possibility of
piston seizing altogether; and, as metallic packings are
fitted to the piston rods — and these have now been
brought to a state of perfection equal to those used in
steam engine practice—no fear need be entertained con-
cerning trouble in this direction, and the minimum of
attention is required.

Ignition Gears.

Generally speaking, the old type of low-tension igni-
tion gear still finds favour, but for reliability and
minimum number of parts likely to give trouble, the
high-tension magneto cannot be excelled. The spark-
ing plugs, even with this type of gear, require renewal
from time to time, but this is not a costly item. With
the high-tension magneto the minimum attention is
required, and there are no batteries to charge.

Owing to the absence of gears, valves, and tappets,
this four-cylinder engine operates as silently as the ordi-
nary vertical steam engine, and the liberal wearing sur-
faces, combined with the smooth running of the engine,
ensure long life.

For continuous heavy service much has been stated
with regard to the reliability of the gas engine, but the
colliery manager must give careful attention to his side
of business — namely, the production of gas — if he
expects reliability in his engine. In the case of boilers,
softening plants have often to be installed; in a similar
way, in connection with gas producers and coke ovens,
suitable cleanin o- and purifying appliances must be
used. Sulphur has to be dealt with drastically, especi-
ally where big engines are installed, as in all these cases
pistons and rods are of necessity water cooled. In
many cases too liberal a supply of water is used for the
pistons, due to the attendants’ exaggerated anxiety to
feel safe, and acid fumes are condensed on the cool rods,
causing corrosion. Again, any leakage of water into a
cylinder with sulphurous gas will cause trouble, so that
great care should be taken in dealing with this matter.
Dust forms also another difficulty which requires con-
sideration, but this is one that causes very little anxiety
in the ordinary way nowadays.

While speaking of large gas engines the writer has
referred only to the vertical engine, as this appears to
bo the type most favoured, and undoubtedly most suit-
able for direct connection to electric generators; but the
horizontal engine is still favoured by mill engineers, and
for blowing engines, air compressing, and water pump-
ing, through the medium of a tail-rod, it may still
possess a useful sphere of work.

Air compressors of the vertical high-speed type, how-
ever, arc rapidly superseding those of the horizontal
type throughout the country, and therefore it is very
probable that gas .driven air compressors of the vertical
type will also be favoured in the near future.

A meeting of the creditors of Percy Bichard Crossland,
carrying on business at 15, Wellington-street, Hull, under
the style or firm of P. B. Crossland and Company, coal
exporter and colliery agent, was held last week. The state-
ment of affairs set out the gross liabilities at Fl,922 6s. 10d.,
and net assets Fl,001 6s. 9d. Mr. G. A. Bidgeway, of
Cogan House, Bowlalley-lane, Hull, incorporated accountant,
was appointed trustee with a committee of inspection.

SOUTH WALES INSTITUTE OF ENGINEERS.

An ordinary general meeting of the South Wales
Institute of Engineers was held at Cardiff on Thursday,
May 28, Mr. Henry T. Wales, president, occupying the
chair. The following were elected members of the
institute :—Sydney W. Abbott, Cardiff; Henry Clement,
Swansea; S. Rees Cound, Moscow, Russia; J. R. Davies,
Llwyn Helyg, Swansea; John Evans, Morriston; David
Mansel Glasbrook, Swansea; David Lewis, Gorseinon;
E. Sims Rees, H.M. inspector of mines, Cardiff; David
Thomas, Pontypridd; John Henry Thomas, Llanelly;
Arthur Williams, Cross Keys, Monmouthshire; and John
Williams, Pontardawe.

Coal Dust and Stone Dust.

Consideration was resumed of the Fourth Report of
the Explosions in Mines Committee.

Mr. George Hann proposed to place at the shaft
bottom an apparatus which would deliver in the air every
minute during which the pit was working an equivalent
amount of stone dust to the amount of coal dust found
to be going down the shaft. To deal with the dust wave
in transit on the main haulages, it was proposed to place
similar mechanical apparatus, worked by levers by the
trams as they passed over the rails, and at distances
apart on the haulage road which, when a journey passed,
put into the air an equivalent amount of stone dust to
the coal dust made by the journey running through the
air, the coal dust being diluted as made. To reduce the
amount of dust being swept off the trams, these should
be watered by a spray on the double parting before leav-
ing. The floor of the haulage road, where it was not
damaged, by watering, might be watered, as this
materially reduced the amount of dust made. The stone
dust used should be of the finest obtainable, so that it
would be carried into every part of the roadway with the
coal dust. At the commencement the road
should be cleaned with a simple apparatus, con-
sisting	of a	compressed	air jet	in	a pipe,

which	would	be found	effective	in	clearing

dust from holes above timber, wherever the holes
were open cogged, as they should be. The difficulty in
this method of cleaning was the collection of the dust,
but he believed this could be overcome. On some of the
main horse haulage headings the same method by a
mechanical apparatus might be employed where the
amount of dust made was great, but if not these roads
might be stone dust treated by hand from time to time.
Every stall road, if shots were fired, should receive a
dressing before the shot-firing of, say, 50 lbs. of dust, or,
say, 100 lbs. per week. This was found to be sufficient
to keep the percentage of ash in the dust well above
50 per cent., and when shots were fired a large cloud of
stone dust was raised. The question arose, what was
the amount of stone dust necessary to keep an average
colliery at 50 per cent? Every colliery would, of course,
vary, and he roughly estimated that for a colliery of
1,000 tons per day the following w’ould be the maximum

amount required :—	Cwt.

To dilute the dust made in the shaft and what

cannot be prevented from going down ...	20

Main haulage roads ...	...	...	...	60

Main horse roads (largely dust from main haul-

ages previously diluted) ...	...	...	30

Stalls (200, each 25 lbs. per 24 hours) ...	...	44

making a total of about seven tons to eight tons per day,
or *8 per cent, of stone dust to coal produced. The
cost of the mechanical application would, be believed, be
small. An apparatus now being experimented with was
a hopper containing about 20 cwt. of dust. There was a
slide-valve in the bottom connected by levers to the
rails, and as each tram passed, a quantity of dust was
allowed to fall out into the air, the quantity varying with
the size of opening in the hopper. This machine was
working very satisfactorily. It required but little atten-
tion, and the only cost was the filling of it with dust
every two or three days, as required. He believed if
these were put in every 300 yards on a roadway it would
keep the whole length of roadway satisfactorily stone-
dusted. The same end could be accomplished in many
other ways, such as running a tram of dust in front of
the journey, which would distribute stone dust by
mechanical means worked from the wheels of the tram
as they revolve. The drawback to this method was the
difficulty of shunting the tram each journey from the
full to the empty journey and vice-versa. Another way
would be to place a thin sheet iron plate on the top of a
tram on to which was placed a quantity of stone dust,
w’hich would be shaken or blown off in transit. It was
not possible, however, at the present time to give any
results as to this method. If fine stone dust was used,
and this seemed to be the only form of dust which was
likely to be effective, it should find its way almost every-
where where coal dust went, but no doubt a smaller
percentage would go up over the timber. There would
be very little risk of an explosion being carried on by the
dust over timber if the road below was kept with a large
excess of stone dust. If an extra precaution was con-
sidered necessary, shelves of stone dust could be placed
in these parts, so that if there was an explosion this dust
would be thrown into the air as well as coal dust. In
conclusion, Mr. Hann said he believed that stone dusting
could be made a success, and that the main roads to be
face could be kept in a state of 50 per cent. ash. The
method of automatically diluting as the coal dust was
made, appeared to him the most effective and cheapest
method of accomplishing it.

Dr. W. N. Atkinson, H.M. inspector of mines, said
Mr. Hann’s plan of the constant automatic distribution
of stone dust in the mine raised the question of the effect
of breathing this air. In some cases the coal dust going