752

THE COLLIERY GUARDIAN.

April 20, 1916.

the operator obtains a “ release ” of skips in both shafts
before starting the automatic operation. He then intro-
duces the automatic control by closing two small control
switches and locking in two levers, all on the operating
platform. This does not, of itself, start the automatic
operation, so that the hoists may be left standing in this
manner indefinitely. To start the automatic operation,
a master controller is thrown to the automatic running
position, and left there as long as automatic hoisting
continues. According to the positions in which the
skips have been resting, one hoist or the other will start.
Say, for example, No. 1 hoist starts, hoisting its south
skip. The closing of the master controller just men-
tioned energises a small pilot motor, which moves No. 1
hoist controller gradually to the full-speed position in
one direction. As No. 1 controller starts away from the
off position, it simultaneously energises No. 1 generator
field, and actuates a pilot device which releases the
brakes on No. 1 hoist. As the controller moves farther
toward the full-speed position, it gradually builds up the
generator voltage, thereby accelerating the hoist to full
speed.

Toward the end of its trip the travel of No. 1 hoist
actuates a pilot motor which moves No. 2 hoist con-
troller gradually to the full-speed position in one
direction, thereby accelerating No. 2 hoist in a similar
manner, to hoist its north skip. Shortly before its skip
enters the dumping horns, the travel of No. 1 hoist, by
means of cams, one of which is geared to each drum,
moves No. 1 controller gradually toward the off position.
This gradually decreases No. 1 generator voltage,
thereby retarding No. 1 hoist, and just as its north skip
is about to land on the chairs, No. 1 controller comes
into the off position. This completes the retardation
and automatically applies the brakes. No. 1 hoist
stands at rest while No. 2 is hoisting its north skip.
Toward the end of its trip, No. 2 hoist energises the pilot
motor for No. 1 controller so as to start No. 1 hoist in
the opposite direction, i.e., to hoist its north skip.
No. 2 hoist comes to rest in the manner described for
No. 1, and rests while No. 1 is hoisting its north skip.
Toward the end of its trip, No. 1 hoist energises the pilot
control to start No. 2 in the opposite direction, i.e., to
hoist its south skip. The sequence continues in this
manner until stopped by the operator, as described later.

A loading system is used underground by which the
skips are automatically loaded with a predetermined
weight of ore per trip. The reduction of the attendance
required at the foot of the shaft contributes materially
to the advantages of automatic hoisting. The automatic
loading system can be thrown out of engagement in
either shaft so that the hoists may be operated either
automatically or by hand, for purposes of inspection or
adjustment, without hoisting any ore.

To obtain a more rapid operation of the hoists, i.e., a
greater number of trips per hour, when operating auto-
matically a control switch may be thrown, by which
each hoist will be started earlier in the trip of the other
hoist, thus overlapping to a greater extent the trips of
the two. If it is desired to run the hoists automatically
at fewer trips per hour than normal, this is done by
introducing resistance permanently in each generator
field circuit, to give a rope speed lower than normal.

Hand Control.

When the details of design were first considered, one
of the chief problems was the arrangement of the con-
trol so that the transition from hand to automatic opera-
tion, and more especially the transition from automatic
to hand operation, might be made without risk or delay,
and in a manner easily remembered by any operator
acquainted with the equipment. To this end, the levers
on the operating platform which operate the hoist con-
trollers and brakes for hand control are not disconnected
from the controllers or brake engines when running auto-
matically. Consequently, when the automatic pilot
devices are cut in, and the hoists are operating auto-
matically, these levers move back and forth, as if the
hoists were being controlled by hand by invisible
operators. When, therefore, the transition from auto-
matic to hand operation is made during a trip, the brake
and controller levers of both hoists are in the correct
positions, and properly in engagement for hand control.

The automatic operation can be interrupted at any
time during a trip. This is done most easily by throw-
ing the master controller for automatic operation to the
off position, which causes any trip which is under way
at the time to be completed automatically, dumping in
the usual manner, but prevents the next trip from start-
ing. If the hoists are then left standing, and not
operated by hand, all that is necessary to start auto-
matic hoisting again is to throw the master controller
to the automatic running position.

Before the construction work at the foot of the shafts
and in the bins in-the tipple had been completed in all
details, it was necessary occasionally to stop an auto-
matic trip without letting it dump. In such an event,
or when necessary for any reason to transfer to hand
control before completing a trip, the master controller
for automatic hoisting is thrown to the oft position.
Without disconnecting or unhooking any other parts, the
controller lever of the hoist which is running may then
be pulled back to the off position by hand, and as the
controller comes into the off position the brakes will set
automatically. It is now possible to leave the pilot
control of the brakes connected in service, so that the
brakes will release and set automatically, as the con-
troller is moved by hand from or to the off position. Or,
if necessary, on acount of the character of hoisting to
be done, the automatic pilot control of the brakes can
be cut out, in which case brakes and controller will be
controlled separately by hand.

Under all conditions (except when making adjust-
ments in the manner described later), the cams on each
hoist controller remain connected mechanically to the
hoist drums. This cam mechanism thus serves two
purposes >—(1) In automatic operation it provides the
automatic slow-down and stop; and (2) in hand opera-

tion, if the operator does not begin retardation at the
proper point, this mechanism will retard the hoist in
practically the same manner as when hoisting automatic-
ally, thus providing protection against overwinding
when operating by hand.

Protective Devices.

The protective system resembles those of a consider-
able number of large direct-current mine hoists, of the
same general type (except the automatic operation) as
the Inspiration hoists. In the latter, as has just been
noted, the automatic control system provides against
overwinding in hand operation. An additional set. of
emergency limit switches is used, which gives similar
protection in case of failure of the automatic control.
During hand operation there are effective, therefore, two
complete sets of protective devices against overwinding.
For each hoist a hand-operated emergency switch is
provided on the operating platform, and a similar emer-
gency switch is located at the foot of the corresponding
shaft, by means of which either or both hoists may be
stopped quickly from the operating platform, or the foot.
Without appreciable complication, additional emergency
switches may be installed at other points if desired. The
operation of any one or more of these emergency devices
cuts off power from the hoist, and makes an emergency
application of the brakes. An emergency, which affects
one hoist only, acts on the power and brakes of that
hoist only. The failure of excitation or alternating-
current power, which affects both hoists, cuts off power
and makes an emergency application of the brakes simul-
taneously on both hoists.

Adjustments in Service.

When unclutching for changing levels, and when
taking up stretch of ropes, the adjustments are taken
care of as follows :—

On the Inspiration hoists it has been the custom,
whenever the hoists are to be idle an entire shift, to
bring both skips to the collar of the shaft, in order, to
save rusting of the ropes. This is done by unclutching
just as in any ordinary hoist with one fixed and one
clutched drum. If desirable for any reason, either hoist
may be run by hand control either out of balance or
clutched in for balance to operate from other levels than
the regular loading level. When clutching or unclutch-
ing, the adjustments of the automatic control system
are not touched.

If the shafts are sunk to the ultimate depth contem-
plated, and the present loading stations abandoned, the
control can be re-adjusted to operate automatically from
the increased depth. Without changing the adjustment
of the control equipment, it is not possible to operate
automatically from levels differing considerably from the
normal level for which adjustment has been made, but
the system is capable of modification so as to hoist auto-
matically in balance from any level to the dump, with-
out re-adjustment, all the adjustments being taken care
of automatically by clutching in at the desired level.

Stretch of ropes is taken up in a simple manner, which
itself is semi-automatic, and does not require any
measurements. The first time it was necessary, the
stretch was taken up on both ropes of one hoist in about
15 minutes, at the end of which all adjustments were
in shape for hand or automatic operation. The method
is as follows :•—

The hoist is run into an automatic stop, with the skip
on the clutched side resting on the chairs. (This is
effected by the cam which is geared to the clutched
drum.) The controller and cams are now in the proper
position for an automatic stop on this side; but the rope
on this side has unwound farther than normal by an
amount equal to the stretch or slack which it is intended
to take up. This cam is now uncoupled, but the other
cam is left coupled. The hoist is now moved by hand
control just far enough to wind up the estimated amount
of slack, and the cam on this side is then coupled up
to the clutched drum. This operation takes up the
slack on the clutched side, and transfers it to the fixed
side. The hoist is now run, in balance, into an auto-
matic stop on the fixed drum side, which lands the skip
on the fixed drum side on the chairs, and brings the skip
on the clutched side into the dump. The cam on the
fixed side is now uncoupled, and before moving the
hoist to take up slack, the other drum is unclutched,
so as to leave its skip in the normal position in the
dump. The fixed drum is then moved sufficiently to
take up all the slack on that side, i.e., the stretch of
rope on that side, plus the slack transferred to that side
by taking up the stretch on the clutched drum side just
previously. The cam is then coupled up to the fixed
drum and the other drum is clutched in, which com-
pletes the adjustment of both ropes and cams, and leaves
the hoist ready for operation. It is necessary, of course,
not only to take up stretch on each side, but also to
clutch-in at the proper level. During the foregoing
procedure, after unclutching one drum as described, the
same movement of the other drum which takes up the
slack also makes the necessary correction for level.

General Conclusions.

Differences in operating conditions will naturally
require different methods of control, so that it is to
be expected that for large automatic mine hoists, which
may be built in the future the control system will differ
from the Inspiration system in several respects. How-
ever, the exhaustive investigation of the subject which
preceded this installation, and the experience gained in
the adjustment and starting of the Inspiration equip-
ment, make it possible to determine readily the
feasibility of other proposed automatic hoists for
different conditions of operation. The experience thus
gained makes it practicable, moreover, to build equip-
ments for greater depths, higher speeds, or other
exacting conditions for which, without this experience,
it would be impossible to make designs with reasonable
certainty of success.

The application of automatic mine hoists will always
be limited by the fact that operation cannot be truly

automatic, except where the conditions of hoisting are
reasonably uniform. In other words, where, under
prevailing conditions, the attendance of an operator is
required practically continuously throughout the shift in
order to change levels, hoist or lower loads out of
balance, or handle men, it is impossible to realise any
practical advantages by operating automatically during
the short periods of hoisting ore regularly from any one
level. On the other hand, entire uniformity is not
necessary in order to make automatic operation practic-
able. As an illustration, consider the case of a main
hoist serving a few levels, and an auxiliary hoist in the
same hoitst house handling all men, timbers, supplies,
waste, etc., for all the levels served by the main hoist.
Conditions 'of operation may possibly be sufficiently
favourable so that if the main hoist is arranged for
automatic operation (or for semi-automatic control from
the level stations by the skip tender), the operator for
the auxiliary hoist will be able to take care of the hand
operation required on the main hoist.

It may reasonably be anticipated that from time to
time various mine hoisting projects will come up for
consideration in which the possibilities offered by auto-
matic hoisting should by no means be dismissed without,
investigation.	*

THE PRESSURE OF GAS IN

COAL BEDS * '

By N. H. Darton.

(Continued from page 520.)

Effects of Variation of Atmospheric Pressure on Gas
Emanation.

It is a very old and deeply seated idea that a close
connection exists between the weather and the amount
of firedamp in mines, and even before the barometer
was invented coal miners regarded increased gas emis-
sion as an indication of the close approach of stormy
weather. The idea has also been prevalent that explo-
sions are most frequent at times of low atmospheric
pressure or storms. Sir Frederick Abel showed this
opinion to be largely erroneous. He gave a list of
explosions during the years 1875 to 1885, involving the
loss of 2,229 lives, and by reference to weather records
showed that only 17-4 per cent, of the mortality was at
a time when the barometric pressure was below the
average, and that half of the explosions occurred when
the pressure was increasing. If the frequent small acci-
dents due to various causes be excluded, three out of
four of the explosions were at times of high pressure or
anticyclonic conditions. We now know, furthermore,
that many of these explosions were caused by dust
ignited by some accidental explosion, and may have had
no relation to increase of gas in the mine.

It is generally -conceded that diminution of atmo-
spheric pressure affects the liberation of gas from coal,
especially from old workings and crevices where the gas
has accumulated. This relation, the effects of which
have been repeatedly noticed by miners, has been fully
substantiated by elaborate scientific investigations. In
places where most of the escaping gas has been under
notable pressure in the coal, the volume emitted cannot
be materially affected by a change of atmospheric
pressure. Various observers have shown that as gas
approaches a face of coal, its pressure gradually
diminishes, and in the outer few inches becomes very
low. A “ fall of barometer ” of lin. indicates a diminu-
tion of atmospheric pressure of nearly -J-lb. per sq. in.
Such a change taking place in a few hours must
decidedly affect the equilibrium of the atmosphere in the
mine. The chief result is an expansion of the air, a
decrease of 41b. in pressure causing an expansion in
volume of about one-thirtieth, or 3| per cent. As the
expansion is gradual, the results can have no direct effect
on the strong air currents of the main ventilation; but
the still air in the old workings and in crevices would
be affected by it, and some gas, held in the coal at the
pressure of the atmosphere before the change, would be
given off when the pressure was relieved. An air
current travelling 500 ft. a minute—a not unusual rate
in some gaseous mines—has a pressure of only about

1	oz. to the sq. in., equivalent to about 0-14 in. of baro-
metric change.

The volume of gas that may be forced out of old
workings by changes of atmospheric pressure may be
more clearly understood if considered on a quantitative
basis. Assume that an area of old workings, 100 acres
in extent and 10 ft. high, is filled with still air carrying

2	per cent, of methane, and having outlet to an air
current of 20,000 cu. ft. a minute. If there were 50
per cent, of open space, the volume of methane in these
workings would be 440,000 cu. ft. As a barometric fall
of 1 in. causes an expansion of about 3 per cent, in a
given volume of air, a decrease of atmospheric pressure
of 0-1 in. would expand this still air 0-3 per cent., and
drive 1,320 cu. ft. of methane into the airway. If one
hour were required for the barometric change and
re-establishment of atmospheric equilibrium, the rate of
discharge would be about 22 ft. a minute, which would
add to the gas in the airway only 0-11 per cent, of
methane. However, the change might disturb the
general equilibrium, and start the flow of the entire
body of still air in the old workings into the return. In
the 20 hours or more that would be required to drain
the 100 acres at the rate of 20,000 cu. ft. a minute, the
methane increment in the air current would be 1-8 per
cent., which would, of course, be a most decided change,
whatever the normal content of the return air.

In many mines there are vast areas of old workings
in part not well ventilated., and the air in these con-
tains more or less methane. The Prussian Firedamp
Commission found that in the Ath-Gouley Mine ("Wurm
coal field) the spaces amounted to 9,110,000 cu. ft., and

* From Bulletin 72 oi the U.S.A. Department of the
Interior, Bureau of Mines.