726

THE COLLIERY GUARDIAN

October 8, 1915.

not been previously turned to the same extent, and,
whoever benefited by the paper, he was quite sure that
his firm’s collieries would. He had thought that they
had a thoroughly up-to-date installation, and he still
thought so—that was if large slow’-running compressors
and large pipes went toward the building up of what
should be an economical plant. Their compressors were
large and slow running, and he presumed they had a
comparatively reasonable friction in their pipes, but yet,
in a set of compressors which were normally running
at about 28 strokes, Mr. Mavor’s representative showed
them that they had to run 11 strokes to keep up the
pressure without using any machine, pumps, or any-
thing else for which they compressed the air. He felt
very much disgusted with a result like that. He thought
probably Mr. Mavor’s way of testing was a much more
satisfactory one than that which they were using. If
they wanted to assure themselves that the leakages were
reasonable, their practice had been, at the week-end, to
run the pressure up to, say, 601b., which was their
normal pressure, and to observe the time it took to go
down to a certain point. If it took three hours to get
down to 15 or 201b., they considered that their leakages
were quite reasonable. But when they got a diagram
showing that the principal loss was sustained within the
first half-hour, then it was quite apparent that their
observations should be made in that wray. That fact
was a simple one, but still they had not adopted the
course referred to. They did adopt it now. It was for
little things like that that he valued Mr. Mavor’s instruc-
tion. It had certainly convinced him that they must in
the future be more guarded about the application of
compressed air in the mine. They must not use it for
what he should call illegitimate purposes. They were
compelled to use it for, say, haulages far in-bye, and for
coal-cutting, but to adopt compressed air as a power for
pumping from the pit bottom to the surface, which some
of them did pretty extensively in West Yorkshire, or for
working hauling engines close to the pit bottom—well,
he thought Mr. Mavor would have dispelled all illu-
sions that people were having satisfactory plants of that
sort. At all events, his were quite dispelled.

Mr. G. Blake Walker said there was a good deal in
Mr. Mavor’s paper that had caused them all to think
very much, and to correct erroneous ideas that they
had as to the amount of efficiency they were getting
from compressed air. The importance of really know-
ing for themselves what was being done, as Mr. Mavor
urged, must be obvious to everybody. To put in meters
and gauges to test the volume of air passing in any
given range of pipes, or the loss of pressure, was a most
economical and cheap thing to do. He would go a step
further and say that he did not think they were wise,
from an economical point of view, in not having some
person specially appointed, in a large district, to devote
his whole time to supervising the compressed air mains
and machinery used in connection with them. They all
knew that their managers and deputies had plenty of
work to occupy their attention, and yet it was only
these persons who, as a rule, were left to look after
the compressed air distribution and use in the mine.
If, where there was a sufficient amount of machinery to
justify it, they had a smart trained man, with some
engineering knowledge—and such men were not now
difficult to get—whose whole business would be to test
the quantity of air passing, leaking, and being used in
each machine, he thought that his wages would be
a very small fraction of what they would save. They
knew that if they had half-a-dozen coal-cutting machines
in a district, some were in good order and some were
not, but so long as those which were not in good order
were cutting a reasonable amount of coal they did not
enquire too curiously into how much air they were using.
In dealing with electrical machinery they were bound to
take note of the amount of current that was being used,
and why should not the same thing be done with regard
to compressed air? He said at Leeds that compressed
air, if it was to be made from steam specially generated,
was a very expensive power, and that they ought to
generate it, where they required it, in large quantities
as cheaply as possible. He would only further mention
that in Prof. Schultze’s paper (Colliery Guardian,
July 24 and 31, 1914) on the economics of a German
colliery, which appeared in their last year’s Proceedings,
there were some very interesting facts as to the waste
of compressed air. It had even been used as a ventilating
medium where shots had been fired, the fumes having
been cleared out to a certain extent by opening the end
of the compressed air pipes. Considering how very
costly compressed air was, anything of that kind was
very wasteful and foolish. He could earnestly support
what Mr. Mavor had said as to the value of measure-
ment. Mr. Mavor was at his colliery that morning,
and they were looking at some diagrams. One, by self-
registering gauges, was almost identical at the com-
pressor and at a point 1,200 yds. in-bye from the shaft.
During 24 hours, the two ranges of pressures followed
each other with a difference of only some 2 lb. They
thought that perhaps the gauges were not synchronised,
but the curious thing was that when the one in the pit
was brought out it was found to be registering 1 lb. less,
and not 1 lb. more, than the one on the surface. The
pressures were about 60 lb.

Mr. Mavor, who had to leave in order to catch a train,
replied at this point, but on the understanding that the
discussion would not be closed that day. He said Mr.
Lloyd had spoken of the advantage of adhering to a
rather smaller hose pipe, in that they had wire drawing
of the air, which to a certain extent checked the racing
of the engine when running at full speed, and gave them
sufficient pressure in starting the coal cutter. He (Mr.
Mavor) considered that quite a mistake. It was impor-
tant to realise that wire-drawing compressed air was an
entirely different thing from wire-drawing steam. When
they wire-drew steam to a moderate extent, they did not

sacrifice the energy : they had a larger volume, but they
retained the energy in the steam, and that energy was
available for use in the steam engine. But the condi-
tions were entirely different in the case of compressed
air. The energy was really not contained in the com-
pressed air in the same sense that it was contained in
the steam. If they dropped the air pressure by wire-
drawing it, they absolutely lost the available energy—
they still had energy in the air, but it remained in a
less available form. If they wire-drew it from 401b.
down to 301b., what they lost was what was required to
put into the air to raise it from 30 to 401b., so that to
wire-draw air for any purpose at all was a very extra-
vagant proceeding. With regard to the form of
coupling, the use of an iron pipe inside a hose pipe very
seriously reduced the area of the pipe, and he very
strongly advocated a form of full-bore coupling, which
was quite a feasible proposition. It involved a slightly
conical piece to insert in the bore of the hose, the bore
of each opening with a right and left hand screw. There
was no difficulty about making a coupling to give them
the advantage of the full bore instead of reducing the
2 in. hose down to something like 1| in. diameter, which
meant a very serious loss of pressure at each junction,
of which there were sometimes several in a hose. As to
Mr. Lloyd’s suggestion that the curves should relate to
longer lengths of hose, Mr. Mavor said the tests
recorded on 20 yds. of hose were consistent with a large
number that he took at 40 yds. In actual practice he
did not go above 40 yds., because he considered it highly
improper to use a trailing hose of more than 40 yds.—
it involved a quite too extravagant loss to make it a
feasible economical proposition. Mr. Lloyd also asked
how the correction for temperature and pressure was
made in connection with the tests. In the paper he had
pointed out that with each instrument the maker gave
a chart or scale, which referred to a multiplying con-
stant which must be used for its corresponding pressure
or temperature. They must multiply the indication on
the dial of the instrument by the constant which they
found from the table, which made the correction for
pressure and for temperature.

Mr. Lloyd asked Mr. Mavor to enlarge a little on this
point. He took it that when the observations were
made the air pressure would be varying very considerably
according to the starting up and running of the
machines. They would be observing the pressure more
especially by an independent gauge, he took it, and
would have to take the mean of the various pressures to
get the correction.

Mr. Mavor said the instruments w’ere fixed up along-
side each other, so that simultaneous readings might be
taken. They must take a series of almost instantaneous
observations of the pressure and of the rate of flow meter.
Mr. Walker had very correctly pointed out that if they
were using power extravagantly it was very important
that they should generate it as cheaply as possible. That,
in a sense, was quite true, but the production of power
was rather a problem apart from his paper. Suppose
they had a dynamo requiring 1,000 b.h.p., and in the
same engine room, alongside, they had an air compressor
requiring 1,000b.h.p., it was quite as important to have
the price of the 1,000 they were using for driving the
dynamo as to have the price of the 1,000 for the com-
pressor; so that, while cheap and economical production
of power by every possible means was to be aimed at,
that did not go beyond the very general way in which
Mr. Walker put it. It was not concerned with the
paper, because the production of power was one thing,
and the utilisation of that power was another. No
matter how economically they generated their power—
even if they halved the present cost—that should not
condone extravagance in the use of that power. The
absolute money saving, of course, in economising cheap
power was less than that saved by economising expensive
power, and he should be afraid that, if colliery officials
had the idea that the power was very cheaply made so
that it might be extravagantly used, it would not, in the
long run, lead to much economy. He was very much
indebted to the members for the kind reception they had
given to his paper. He would very carefully consider
all further contributions to the discussion, and reply to
them in writing.

Mr. W. H. Chambers, continuing the discussion, said
up to the present his firm had only employed compressed
air in a very limited degree, but conditions had now
become such that they had -to use power not only for
coal cutting, but were proposing to use it extensively
for conveyors and also for pumping engines. They had
to economise in labour and wages as far as possible in
these times. They had put down a large compressor
engine as a first unit. How it would be extended he
did not know—it would depend upon how it paid. In
order to avoid wastage of air as much as possible, all
the pipes leading from the compressor had electrically
welded joints. He was very much imbued with the
notion that a great deal of the effectiveness of com-
pressed air lay in having plenty of air receivers. He
was installing a series of reservoirs as close up to their
work as possible, as well as bn the road. In that way,
he hoped to save blowing air away when the engines
were stopped, and not consuming much, and, on the
other hand, to have more in reserve than the engines
would give off if they all happened to be working at
a time together. He was also rather impressed with the
idea that if the engines that were feeding from a
receiver at the far end happened to be stopped, the flow
of air up to the full pressure would go on until he got
a full pressure in the receiver at the far end, and in that
way maintain the pressure for a longer period than he
could if they were dependnt on the flow of air through
the pipes alone: and perhaps have sufficient reserve
in those air compressors that, if it began to blow off,

they could stop the engine for a while and they would
have enough air in the pit 'to carry on the work some
time when they were not making any, and not waste
power in that way. He should like to know the experi-
ence of other people in that direction, because he was
very much imbued with the idea.

Mr. E. W. Thirkell said he could bear out exactly
what Mr. Chambers had said with reference to the pro-
vision of ample air room, large pipes, and plenty of
receivers, and particularly to have those receivers near
to their work.

Mr. G. H. Barraclough considered that large pipes
were better than receivers. If they had receivers and
small pipes, they would just have the same trouble as
if they had no receivers. Large pipes were the salva-
tion of compressed air in any mine. They might get
their pressure for large pipes, but, with receivers, they
would get it up at a certain time, and then, as soon
as the engine commenced, they would find that they
did not retain it.

Mr. Chambers said he quite agreed with Mr.
Barraclough. His object in having the receivers was to
supplement the pipes, not to reduce the size. He was
using 10 in. pipes down the shaft.

Mr. Barraclough : We have 12 in. pipes down the
shaft, and a long way in-bye.

Mr. Chambers, in reply to the President, said the
electrically-welded joints on his pipes were rigid.

The President : Then you do not get over the diffi-
culty of loss from breaking of a pipe in that way; or
have they sufficient elasticity to bend to the movement
of the ground?

Mr. Chambers : Yes. They are steel pipes, and they
would give for what movement there is in the ground
where they are laid. Of course, we cannot take’ them
right in-bye, to the far end, electrically welded, because
we dare not take the machinery to do it with.

The President said an interesting idea occurred to
him some years ago, and he should like to know whether
it had ever been done. Where they had a colliery two
miles underground, and they had to take compressed
air, his idea was to put a borehole down to the working
place, or as near as they could get, to line the borehole
with tubes, say, 12 in. long, and take the compressed
air straight down to the place, doing away with pipes
from the pit bottom to the working place. There were
places in old collieries where, if they could get a line of
borehole satisfactorily in that way, they could get com-
pressed air direct almost to the points where it was to be
used.

Mr. J. H. W. Laverick thought it would be a good
plan if the users of compressed air subdivided their cost
sheet for colliery consumption into different parts, and
had one part headed “ compressed air.” It had fallen
to his lot to dispense with compressed air. In the first
place, he found a compressor which he knew was an
abominable extravagance. It was supplying hauling
engines, and the hauling engines got to such a state, as
they got further out, that either they had to be replaced
or he had to go in for a new compressor. However, it
occurred to him one day, “ Why not knock off the air
cylinders from the compressor on the bank and use the
steam cylinders, and stick a drum on and put the rope
direct on to the engines on the top that formerly com-
pressed the air?” He did that, with most astonishing
results. It was a practical illustration of the inefficiency
of compressed air. He used to draw about 20 tubs at
a time on an incline of 4 or 5 in. to the yard, but with the
new arrangement he had not the slightest difficulty in
drawing up 50, 60, or even 70. Later on, he had to do
with a colliery where pumps were driven by compressed
air. That appeared to him to be a most extravagant
way of pumping water, and he had not the slightest com-
punction about stopping the compressor, and the haulage
engines also, and substituting electricity. Now, as years
went on, they advanced. Compressed air had made
progress. Only a month or six weeks ago he was a party
to giving an order for a turbo-compressor. He did not
know what sort of fun he would have with it; he would
have to wait a few months before it was got to work.
But that seemed to him to be the one chance that com-
pressed air had at collieries. If they produced com-
pressed air out of live steam, at the price that small coal
was to-day, and likely to be in the future, he considered
it was a very expensive luxury, but, if they had exhaust
steam from winding engines and other sources, then he
thought their chance, by means of the turbo-compressor,
might certainly be very much better.

Mr. T. Beach asked Mr. Laverick w’hat provision he
was making, with his turbo-compressor, for getting his
compressed air on the night shift, when the winding
engines were not working. Was he going to rely on
the exhaust steam from the fan, or to have a mixed-
pressure turbo, so that he could use live steam?

Mr. Laverick said they had a pair of rotary com-
pressors which were only about five years old. They
wound coal double shift, so that they would have the
exhaust steam available for certainly 18 hours out of
the 24, and they would be able to fall back upon the
compressors for the rest.

Mr. Blake Walker said he had no doubt Mr. Laverick
had seen the turbo-compressors at New Hucknall. He
believed, from what Mr. Muschamp had told him, that
they were quite satisfactory—in fact the company were