702

THE COLLIERY GUARDIAN.

April 14, 1916.

•but because of the difficulty of making a reducing valve
.that permits the flow to be interrupted. With such a
system it is necessary to set the valve to deliver oxygen
at a rate that supplies the demands of the wearer when
putting forth his utmost exertion.	,

At all other times the supply is excessive, and the
surplus must be allowed to escape through a relief valve.
Besides being wasteful of oxygen,, this .method causes
considerable fluctuation in the pressure within the
apparatus, and at times makes breathing difficult.

Fig. 2 shows the apparatus in use, with its protecting
cover of aluminium.

It was felt that the first step in improving the
apparatus should be to design a more perfect reducing
valve. A series of experiments led to the construction
of a reducing valve that satisfies every requirement. An
exterior view of this valve attached to the supporting
frajne is shown in fig. 3. Fig. 4 shows the interior
construction.

A magnalium casing A contains the valve-closing
toggles, which are actuated by a flexible metallic bellows
B. Except for a rubber gasket at the junction of.A and
B, all the parts are of metal.

Extreme sensitiveness is obtained, and sluggishness
is avoided, by using knife edges for all the bearings of
the toggles, and by having the whole system come into
nearly a straight line when the valve is on its seat.
Perfect tightness and freedom from “ creeping ’’ are
assured by the use of a Monel-metal valve and a
hardened steel seat.

When this reducing valve is attached to a cylinder of
gas at a pressure of 150 atmospheres, the pressure within
the bellows, when the outlet is closed, is about one-sixth
of an atmosphere. This remains constant, even after
the outlet has been shut off for several hours.

Fig. 4.

Such a reducing valve makes it possible to admit
oxygen intermittently to the breathing bag in the exact
quantity required by the user under conditions varying
from complete rest to extreme labour.

All parts of the breathing apparatus are mounted on
a frame of steel tubing, which is carried at the back.

Referring to fig. 3, the cylinder or bottle of compressed
oxygen, 0, has a stop valve V, connected to the reducing
valve R, from which the gas at low pressure passes by
way of the tube T, past the safety valve SV, to an
admission valve within the breathing bag as shown in
fig. 1. The safety valve has a whistle in its outlet, and
blows off at half an atmosphere. The whistle is to give
warning of leakage at the reducing valve.

The cooler C, of blackened copper, supports the
breathing bag, on which rests an aluminium flap F.
This flap rises and falls aS the breathing bag expands
and contracts. It bears on and holds open the admission
valve I until the bag is about half full of oxygen.

The operation of the apparatus is as follows :—

On inhalation, air from the breathing bag lifts the
inhalation valve IV, and passes by way of the flexible
tube and mouthpiece to the lungs. Exhaled breath
passes to the exhalation valve (hidden by the corner of
•the cooling can), thence down a flue to the left-hand
end of the absorber, thence through the absorber, where
it loses its CO2, up through the cooling can C, where it
loses heat, and into the breathing bag B.

Whenever the supply of oxygen in the bag gets low,
the flap F opens the admission valve and a fresh supplv
enters.

The absorbing can AC has been the subject of much
experiment. The 'form adopted contains 20 vertically
arranged sheets of fine iron-wire gauze, held parallel to
each other and one-fifth of an inch apart by spacers.
Before being enclosed in the can, the bundle of gauze
sheets is dipped into molten caustic soda (NaOH) con-
taining 20 per cent, of water. The caustic solidifies on
the gauze when cold, forming reinforced plates about
a-sixteenth of an inch thick, between which the expired
air passes.

This makes an efficient absorber of C03, and has the
further advantage that the plates maintain a uniform
surface from which the condensed and chemically pro-
duced moisture constantly drains away, carrying with
it t-he newlv-formed sodium carbonate, so that the

capacity of this absorber is nearly constant until the
active material is all used.

A pressure gauge or “ finimeter,” which is read by
touch instead of sight, and that sounds an alarm when
the oxygen in the cylinder has been reduced to 30 atmo-
spheres, completes the apparatus. The whole device
is suspended from the shoulders by leather straps. In
this apparatus there is a minimum of parts, and the
connections have been made without the use of rubber
wherever possible. A simple mouthpiece and nose clip
is used instead of a helmet, experience having shown
•that the helmet is so dangerous that its use has been
abandoned by the Bureau of Mines. The weight of the
complete apparatus is 301b., which is considerably less
than that of similar devices.

The pressure within the apparatus is maintained
slightly above that of the atmosphere by the pressure of
the weighted flap F on the breathing bag. Conse-
quently, if the apparatus is punctured, or if a crevice in
any part of the system opens, the leakage will be out-
ward only.

Exhaustive, tests of the new apparatus have shown
that it permits unusually free breathing, that the air
supplied is always comfortably cool, that as the front
of the body of the wearer is entirely free, he is not
hampered in his movements, and that the parts of the
device are well protected against accident. The entire
apparatus can be quickly taken apart or put together
with a wrench and screwdriver.

THE SINKING AND EQUIPMENT OF A
CIRCULAR SHAFT.*

By James Nisbet.

'The shaft was sunk at Dykehead Colliery, Larkhall,
the owners of which are the Summerlee Iron Company
Limited. The colliery has been worked for over 50
years, during which time coal getting has been confined
to the upper seams. These seams have been worked
by a day mine (forming the downeast), and by a
rectangular shaft (forming the upcast), from both of
which coal lias been drawn. As that day mine will
shortly cease to be available for this purpose, it became
necessary to sink another shaft, to serve as a downeast,
and by which the output might be maintained and some
of the lower seatns won.

The surface overlying the coal is composed of sandy
clay of considerable depth, and the surface barring of
the previously mentioned rectangular shaft has had to
be repaired from time to time on account of its decay,
and consequent bulging into the shaft. This movement
was in each case inevitably accompanied by a sinking
of the surrounding ground, which more or less dis-
turbed the level of the bell-crank beams, and of the pit
mouth generally. It was therefore decided to make
the new shaft circular, as being the stronger and more
readily secured form, and to enclose its mouth in a
foundation block of concrete resting on the solid clay.

The Sinking.

The shaft is 13|ft. in diameter, 426 ft. deep, and is
lined with brickwork throughout. Generally, the brick
lining is 9 in. thick, but, at certain parts, the thickness
is greater. From the rockhead to the surface, a distance
of 46 ft., the brickwork is backed with concrete 12 in.
thick, rammed solid for the purpose of shutting off
effectively the entrance of surface water. A shaft of
this diameter provides ample accommodation for two
cages, each carrying two 10 cwt. hutches end to end.
As the shaft is comparatively shallow, single-deck cages
are sufficient to meet the capacity of the screening and
washing plants.

The centre of the proposed shaft having been pegged
off, marks were fixed at points not likely to be disturbed,
from which intersecting lines could at any time be
stretched so as to determine the centre, after excavation
had commenced. Three of these marks were on a line
passing through the centre of the pit on the proposed
centre line of the drum of the winding engine.

Support of Surface Clay.

A square frame, of 11 in. by 4 in. white pine planks on
edge, and measuring 18 ft. by 18 ft. inside, was let into
the surface, and levelled up. Each side of the square was
equidistant from the centre, and two of them were
parallel with the centre line of the winding engine drum.
This frame was put in to mark the limits of a concrete
surface foundation block, and to form a guide and
backing for the shoring for the support of the sides of the
excavation, which was now commenced, and was cut
down plumb from the inside of the frame. At a depth
of about 3 ft., another frame, of 9 in. by 3 in. planks on
edge, and measuring outside 17 ft. 8 in. by 17 ft. 8 in.,
was laid down on the bottom of the excavation, con-
centric with the frame above.

Behind this frame, at close intervals all round the
sides of the excavation, pieces of 6 in. by 2 in. battens,
about 6 ft. long, were entered on end, and the heads
held back by a similar frame fixed at a higher level. As
the excavation deepened, the battens were driven down,
in order to guard against any slipping in of the sides.
At about 6 ft. from the surface a third and similar frame
was put in to hold back the feet of the battens.

The excavation was now reduced to a diameter of
17 ft., and the sinking of the circular shaft commenced.
The sides of the shaft were supported through the
surface clay, and in soft rock, where met with, until the
permanent lining was put in, by using angle-iron rings,
behind which backing deals 1 in. thick were wedged
against the sides of the shaft. These rings were of 3 in.
by 3 in. by |in. angle iron, in four equal segments,
curved to form a true cirole measuring 15 ft. 4 in. in
diameter outside.

* From a paper read before the Mining Institute of
Scotland.

The segme.nts were joined together with iron fish-
plates, 3 in. by i in. by 21 in. long, with four f in. bolts
to each joint. This size of ring was used when sinking
■through rock, where the cutting was reduced to a
diameter of 15|ft. In the surface clay the rings, were
enlarged by introducing between each of the four joints a
short piece of angle iron 18 in. long, and by bolting up
through long fish plates with .seven bolts to each joint.
Three of the bolts passed through the added piece of
angle iron, and held it in position;

The ring thus formed was not truly circular, but was
near enough for the purpose intended, and its adoption
made one set of rings serve. Holes were bored in the
bottom flange of each segment for long-screwed bolts,
screwed at both ends, whereby the rings were hung from
supports or from one another. By adjusting the nuts on
these bolts, the rings were levelled up and hung at the
desired distance apart—namely, from 3 to 5 ft.

The first ring was put in 2 ft. below the point at which
the circular sinking commenced. It was hung from
battens supported on the bottom frame in the square-cut
excavation. Others were placed at intervals, hung one
from the other, as the sinking deepened through the clay.
For the first 12 ft. of the sinking, the excavated clay was
cast out in. stages to the surface. Thereafter, down to
148 ft., a 3-ton steam crane, with a 65-ft. jib, was used.

This crane was fixed to one side in such a position that
it would also serve for the erection of the pithead frame,
and for handling the heavier portions of the permanent
winding engine when being erected. Sinking kettles of
the ordinary tipping type were used. Two of these were
in service, except at the earlier stages.

Every short distance, as the sinking progressed, radial
measurements wore taken from a central plumb line, to
ensure bhat the shaft was being sunk truly vertical and
circular in form.

At this stage., from the nature of its suspension, the
plumb line had to bo placed in position each time that
measurements were taken. To ensure that on each
occasion it would be hung in exactly the same position,
the following simple plan was adopted :—A piece of 4 in.
by 41 in. pitchpine slide was laid diametrically aerosis
the shaft, and its ends, which were marked, fitted into
close-ended shoes fixed to the frame bounding the square
excavation. The centre of the shaft was marked on this
spar, and an auger hole bored vertically through it at the
mark. This hole was covered by a thin steel plate with
a small hole in it, only large enough to admit the plumb
line. Before screwing down, the plate was adjusted, so
that the hole in it was exactly over the centre of the
shaft. It was, therefore, only a matter of winding up
the plumb line, when no longer required, and lifting the
spar out of its fixture and laying it aside with the assur-
ance that it could be replaced in exactly the same
position when required. The plumb-bob was of cast
iron, cylindrical in shape, measured about 20 in. long
by 3| in. in diameter, and weighed about 60 lb. It was
turned true to ensure balance, had one end pointed, and
■the other flat. In the centre of the latter an eyebolt was
screwed, to which the plumb-line was attached.

Bricking Seat in Clay.

At a depth of 37 ft., while still in the surface clay, it
was thought desirable to form the first bricking seat,
and to put in the permanent lining of this portion of the
shaft. The last 6 ft. of the cutting had gradually been
reduced from 17 ft. to 15 ft. 10 in. in diameter.

The bottom was levelled up round the sides of the
shaft, and some bricks and mortar were lowered. The
centre plumb-line was then run down, a sump hole in
the bottom allowing the plumb-bob to hang free, well
below the level of the bricking seat.

Bricks, in pairs, placed radially and exactly 6 ft. 9 in.
from the centre plumb-line, were now bedded in cement
mortar, at intervals of about 3ft., all round the circum-
ference of the shaft, and the spaces between these filled
in to template. The complete circle thus made formed
the foundation upon which the brickwork was built.

When at a height of about 3ft., the circularity of the
shaft was checked by a measuring stick from the plumb-
line, and eight plumbing marks were put on the brick-
work at equal distances round the shaft. As the brick-
work rose, plumbings were taken over these marks, and
the portion between each two plumbings built to tem-
plate. The plumbings were checked every 8ft., which
corresponded with every alternate shift of the bricking
scaffold. The first 6 ft. of: the brickwork was built solid
against the tapered sides, thus corking itself into the
clay. From that point, right up to the surface level, the
brickwork is 9 in. thick, and is filled in behind with
cement concrete, rammed hard against the sides. As
the walling progressed, the temporary lining of the shaft
was taken out.

When the brick lining had been carried up to the level
of the surface, concrete was filled in behind. The
timber supporting the sides of the square excavation was
gradually removed, and the whole space filled with con-
crete, which was finished off level and flush with the
top of the brickwork.

The bricks used for the lining were made of blaes con-
taining a small admixture of fireclay. They are 9 in.
long, tapered from 4| in. to 4^ in. broad, and 3|in.
thick, and are all built headers with the narrow end
facing into the shaft. Dowm one side of the shaft, at
intervals of 4 ft., a line of oak blocks was built into the
lining, to provide a means of fixing a column of pipes,
should these be required. The mortar was composed of
1 part of cement to 2 parts of clean sharp sand, and the
concrete mixture of 1 part of cement, 2 of sand, and 4 of
broken brick.

The bricks were loaded into the kettle, and lowered
and emptied—on to the bottom at the commencement
of the bricking, and on to the bricking scaffold when
that was in use. The ashes used for packing were also
lowered in the kettle and tipped on to the scaffold, from
which they were shovelled in behind the brick lining.

The mortar and cement concrete were mixed on the
surface, and filled into strong shallow boxes about 31 ft.