January 31, 1913.

THE COLLIERY GUARDIAN.

227

rotates it on the return stroke, similar to hand-drilling,
where the drill steel is struck with a hammer and the
steel turned after each blow. The object of rock drill
design is to consume the minimum amount of power per
unit of rock excavated. The original rock drills were all
of the percussive type of machine, and were often made
of unsuitable materials, cast iron largely entering into
their construction. Tbe drilling speed was the chief
consideration, and the valve fitted was of the spool or
tappet type. The spool valve was heavy and cumber-
some, and required a large amount of air for the
reversal; whilst the tappet valve proved very unsatis-
factory, owing to the number of breakages of the
tappet-valve levers. In these machines, the number of
blows per minute was about 400, and the air-consumption
about 150 cubic feet of free air per minute. The chief
losses of air were caused by the large waste space due
to cylinder clearance that had to be filled on each
occasion of reversal of the valve by the compression at
the end of the stroke. The valves also moved so slowly
that the exhaust port was uncovered before the air-inlet
valve was closed, thus allowing a certain amount of live
air to blow straight through. In addition, there was no
cut-off, full air-pressure being behind the piston during
the whole of the stroke.

The first improvements were directed (1) to reduce the
dead weight of the valve and to obtain a quicker
reversal, or to lessen the travel of the valve to obtain
the safe effect; and (2) to arrange the cut-off in such a
manner that the air was used expansively. Several
drills were tried with large and small diameter pistons
on the same rod, but these were complicated ; small air
consumptions were obtained, but the cubic feet per inch
drilled was not a very great improvement, and trouble
was also encountered in the freezing of the valve ports.
The air consumption was reduced to about 70 cubic feet
of free air per minute.

A recent type of expansion valve for percussion drills
is that used in drills of the Meco type. Instead of
having a central valve or complicated pistons and air
ports, the valves are of the piston type, with a valve port
at each end of the cylinder, and the air admission direct
into the cylinder itself.

The percussive rock drill is now being superseded by
the hammer drill, except where holes of large diameter
have to be drilled in very hard rock. Hammer drills
were put on the market in 1898, but slow progress was
made in the first few years, owing to the lack of suitable
material to withstand the heavy strain. The introduc-
tion of suitable steel in the construction of these
machines has, however, removed this difficulty. The
average air consumption of the hammer drill is from
30 to 40 cubic feet of free air per minute, but great
improvements have been effected in recent years.
Taking the Meco hammer drill of 1910, fitted with the
flap-valve, the air consumption of this machine was
40 cubic feet of free air per minute, whereas the machine
of the same size at the present day consumes only
27 cubic feet, with a 10 per cent, increase in the boring
speed. This increased efficiency has been accomplished
by cutting down the waste air space in the cylinder and
improving the mechanical construction of the machines.
The Meco hammer drill is now constructed throughout
of forged steel, all the wearing parts being case-hardened
and ground to gauge. The double-valve hammer drill
gives the same boring speed as the old type of flap-valve
machine, but the air consumption has been reduced to
20 cubic feet per minute. The valve-gear of this
machine is similar to the percussive drill previously
described. The number of blows per minute given by
these hammer drills is approximately 2,500.

A recent air-saving device in hammer drills of this
type is the utilisation of the exhaust air from the
cylinder for flushing out the hole by passing the air
down the drill steel, instead of using live air for this
purpose.

The author then gave descriptions of the Holman,
Siskol and Hardy, which he said were typical machines,
well known, and largely used both in coal and metal
mining.

The annual dinner of the Scottish Coal Exporters’
Association was held on the 22nd inst. in St. Enoch Station
Hotel, Glasgow. The Right Hon. the Lord Provost of
Glasgow (Mr. D. M. Stevenson) presided, in his capacity of
chairman of the association. The company numbered about
80. In proposing “ The Coal Trade,” the chairman said that
in Scotland they were gradually getting a bigger share of
the trade, very largely owing to the intelligence of the
Scottish coal exporters. There were many classes of coal in
Scotland which could beat anything to be found on the
Tyneside, and gradually many markets had come to take
that view. Consequently their exports were rapidly
increasing and the reputation of their coals in foreign
markets was such that they were looked upon as second
only to the very best Welsh coal. Mr. Charles Carlow
responded.

MIDLAND INSTITUTE OF MINING, CIVIL, AND
MECHANICAL ENGINEERS.

Some very interesting business came before the
Midland Institute of Mining, Civil, and Mechanical
Engineers at a meeting held at the Great Northern
Hotel, Leeds, on Tuesday, January 21. Novel devices
in electrical pumping, adopted at the Dover Collieries,
were discussed, and other questions laid before the
members were the taxation of mines, and the generation
and use of compressed air in mines. The President
(Prof. F. W. Hardwick) occupied the chair.

The following elections took place:—Members : Mr.
A. C. F. Assinder, New Monckton Collieries, near
Barnsley, proposed by Mr. 0. C. Ellison, seconded by
Mr. 0. E. Rhodes ; Mr. Edgar C. Heal, Apartado 133,
Bogota, Republic of Colombia, South America, proposed
by Mr. J. W. Simpkin, seconded by Mr. C. Heal.
Associate members: Mr. Walter Davies, 5, Winckley-
street, Preston, proposed by Mr. M. H. Habershon,
seconded by Mr. E. Soar; Mr. W. M. A. Kobs, Phoenix-
chambers, South Parade, Leeds, proposed by Mr. G.
Blake Walker, seconded by Mr. J. Wroe; Mr. Gilbert
Turner, Silk stone, near Barnsley, proposed by Prof.
Hardwick, seconded by Prof. O’Shea. Student members :
Mr. Frederick Allott, The Poplars, Low Harley, Went-
worth, Rotherham, proposed by Mr. M. H. Habershon,
seconded by Mr. D. Russell; Mr. G. J. H. Ashwin,
Coverleigh, Wath-on-Dearne, proposed by Prof. Hard-
wick, seconded by Prof. O’Shea; Mr. Harry Bali,
Roundwood, Parkgate, Rotherham, proposed by Prof.
Hardwick, seconded by Prof. O’Shea; Mr. Harold P.
Boot, Hood Hill Farm, Chapeltown, Sheffield, proposed
by Mr. M. H. Habershon, seconded by Mr. D. Russell;
Mr. A. W. Staniforth, Manor House, Todwick, Sheffield,
proposed by Prof. Hardwick, seconded by Prof. O’Shea.

The President announced that the next meeting, at
Barnsley, would be held on March 12, instead of
March 11, as originally arranged.

The Taxation of Mines

Mr. David Bowen then read a paper on “The
Taxation of Mines in Various Countries,” which will be
found elsewhere in this issue.

The President said they had heard an exceedingly
interesting paper from Mr. Bowen, but he personally
.must confess that he would rather have a little time to
study it. He had no doubt they would all agree that it
would be better to defer definite discussion on the paper
until their next meeting, when they would have had
time to study the subject by reading the paper care-
fully. In the meantime he would ask Mr. Rhodes to
propose a vote of thanks.

Mr. H. Rhodes said it gave him great pleasure to
propose a vote of thanks to Mr. Bowen. From the
cursory glance which he had been able to give to the
paper at that meeting, it seemed to him that it might be
described as a monumental work. To some of them
who were not altogether connected with mining in this
country he was sure it would be of the greatest possible
value. He agreed that the best plan would be to
adjourn the discussion.

Mr. T. Beach had pleasure in seconding the resolu-
tion, which was carried, and Mr. Bowen briefly replied.

Electrical Pumps at Dover Colliery.

Mr. R. Herzfeld, Ph.D., then read a paper on
“ Some Novel Devices in Connection with Electrical
Pumping Installations in Mines” (which is given on
page 223 of this issue).

Dr. Herzfeld, in compliance with a suggestion by
the president, added an explanation of the diagram of
electrical connections appended to the paper. He said
that in the middle of diagram 5 there were three
incoming feeders connected to two air-brake switches.
These two switches were so interlocked that both could
not at the same time be put on to No. 2 cable—that was
one point he made in the paper. The two principal
groups of pump motors which were fed from these three
cables were one on the left and one on the right hand
side, each being driven by two motors—No. 1 and No. 2
in each case. From the two air-brake switches in the
middle there were two connections going from each
switch. One was the high-tension connection, going to
another switch on the left, which controlled various
transformers, and one was the connection to the two
pump motors on the left. The same remarks applied to
the air-brake switch on the right side. There was a
connection going to the two motors, and another connec-
tion to the various groups of transformers. These
connections to the motors had high-tension current from
one side and low-tension current from another. The
low-tension came from a transformer which was shown
at the bottom of the diagram, called the drying-out
transformer. The principal switch, which controlled
pump No. 1 and pump No. 2, was shown at the top of
the pump control panel. In both cases, where the high-

tension connections from the cables and the low-tension
connections from the transformer met that switch was
a change-over switch, so that they could either put in
the high tension to run the pump or the low tension to
run the motors.

Mr. H. Rhodes said he took it that the reason why
two motors were put on to one pump was, that in case of
a breakdown of what he might call an inefficient
generating plant they would not be left entirely out.
He also took it that they would have put down a
600-horse power motor in the first instance if they had
had enough powei' available. He noticed that they had
not got a surface condenser in connection with the
plant that Dr. Herzfeld spoke of. As they were close
to the sea, he would like to know what would be the
disadvantage of a surface condenser under those con-
ditions. In that district bad water seemed to be the
difficulty, but a surface condenser was the usual type on
ships, and he should have thought it would have been
the very thing they would have installed at Dover.

Mr. J. Elce proposed that the best thanks of the
meeting be given to Dr. Herzfeld for his paper.

Mr. A. E. L. Chorlton said he would like to enquire,
as a visitor, with regard to a few points in connection
with the installation. In the first place a natural query
was, Why had Dr. Herzfeld divided the motor into two
and not the pump ? They would have almost thought
that it would have been as much advantage, or perhaps
greater, at a little higher first cost, to divide the pump
into two, because he could have raised the periodicity of
the generator, and speeded up either set, in order to get
the increased output. The next consideration which
arose—apart from the paper—was whether, in large
pumping installations, on which the life of a mine
depended, it was not always advisable to have a gene-
rator laid aside for the pumping set alone. They could
then set their periodicity to either a greater or lesser
output, or a greater or lesser head ; and they could also
always start and stop with a closed circuit, which prac-
tically did away with all the switchgear required. He
would like to ask Dr. Herzfeld if he had had any troubles
at all from corrosion, wear, or other difficulties which
pumps usually had to meet. The improvement in the
generator by the addition of fans was now, he should
say, almost common practice ; in fact the outsider was
almost inclined to think that electrical plant was more
or less covered with fans nowadays. He did not com-
ment on the switchgear. It seemed to be ingeniously
constructed ; but what exactly did Dr. Herzfeld gain by
this particular application ? He understood the gain
made by running a single motor at a higher speed, and
thereby getting more than half the output; but he did
not quite follow why Dr. Herzfeld needed to go so far
otherwise. Did he gain materially in capital cost ?
—because that would be very important.

Mr. Mylan said the plant did not appear to be
simple, as he thought the majority of them would
prefer that plants should be. There seemed to be, not
necessarily an inefficient, but an inadequate, generating
plant in the first instance. This, under usual conditions,
was not a very material gain as far as £ s. d. was
concerned, which, after all, was the deciding factor in
the majority of installations of that nature. It was
rather interesting to note the method of starting which
was adopted, but seeing that the whole object of the
generating plant, in the case described by Dr. Herzfeld,
was pumping, it seemed to him that the proper way of
dealing with the problem would have been to adopt
a system by which the pumps were started up by
starting the generating plant. He thought that by
adopting a method like that, with a perfectly simple
switchgear, they would have had equally efficient opera-
tion and a considerable saving in capital cost. His own
opinion of colliery installations—and it was one based
on some little experience, from tbe electrical point of
view—was that they could not have their plant too
simple to do the work. He noticed quite an extensive
use of fuses, at 2,500 volts. He did not think
accepted practice nowadays agreed with the use of
fuses, even immersed in oil, on colliery work. The
general practice appeared to be to use circuit-breakers
which, he thought, were far preferable.

Mr. Gr. Blake Walker, in seconding the vote of
thanks, said none of the recent improvements in mining
machinery were more admirable than the adaptation of
turbine pumping to the drainage of mines, and he was
always struck with wonder that the principle of these
machines was capable of dealing with such pressures.
He believed there were still higher heads dealt with by
single pumps than in this particular case, but this was
a very great head. They heard that in one shaft there
were 900 gallons a minute, and that in the second shaft
900 gallons a minute were anticipated, and the plant
was designed to deal with 1,800 gallons a minute. Was
not that rather taking for granted something that