Vol. CV.

THE COLLIERY GUARDIAN

AND journal of the coal and iron trades.

FRIDAY, JANUARY 31, 1913

No. 2718.

SOME NOVEL DEVICES IN CONNECTION WITH
ELECTRICAL PUMPING INSTALLATIONS
IN MINES *

By R. Herzfeld, Ph.D.

An electrical pumping plant which shows several
interesting new features has recently been started at
the Dover Collieries. When the present management
commenced operations in the second half of 1910, they
found one shaft (No. 2) 14 ft. 5 in. in diameter practi-
cally finished. The shaft is tubbed over the greater
part of its depth, and reaches the first workable seam of
coal at a depth of 1,275 ft. Another shaft (No. 3), 18 ft.
in diameter, is being sunk, and has reached a depth of
1,050 ft. A great accumulation of water was known to
exist at a depth of about 1,150 ft., and it was estimated
that a maximum of 900 gallons per minute would have
to be dealt with in order to keep No. 2 shaft dry, and
an additional 900 gallons per minute if any appreciable
progress were to be made in the sinking of No. 3. For
the initial operations both shafts were unwatered by
means of cages attached to the ropes; but this
method, if not inefficient, had sooner or later to be
abandoned, in order to make the shafts available for the
raising of coal. It was therefore decided to erect at the
1,275 ft. level, close to No. 2 shaft, an electrical
pumping plant with a capacity of 1,800 gallons per
minute; and it was the intention to drain both pits from
this one place, as it was known that there was a connec-
tion between No. 2 shaft and a borehole at the bottom
of No. 3. There was at the colliery a power-house
containing two high-speed reciprocating steam sets,
each of a capacity of 250 kw., exhausting into the
atmosphere. The current produced is three-phase,
50 cycles, 2,500 volts. It was decided to make use of
these sets to deal with the first 900 gallons, and to
double the capacity of the generating station, when the
winding of water would have to be abandoned altogether.
The new installation, therefore, consisted in the first
place of two feeders, each capable of carrying the total
capacity of the generating plant—namely, 500 kw.—
and of two centrifugal pumps, each capable of raising
920 gallons per minute from a depth of 1,275 ft. It will
be noted that whereas for a delivery of 900 gallons there
was a complete stand-by in the feeders and pumps,
there was nothing to fall back upon in the generating
station, in case anything happened to one or the other
of the two generating sets. In order to meet this
emergency, the pumps have been so designed that with j
only one of the two generating sets working, either of I
them can still deliver 375 gallons per minute at a !
slightly reduced speed. It will be interesting to state |
the results of some careful tests made with these pumps I
with various speeds and duties, as follows:—

Fig. 1.-Plan.

D

C

G

Fig 3.—Section
on Line G H
of Fig. 1.

Fig. 2.—Sectional Elevation on Lines AB ano E F of Fig. 1.

Section on Line AB i	Section on Line EF

	(1)	(2)	(3)
Gallons per minute 			375 ...	760	920
Manometric head, in feet		1,353 ...	1,320	... 1,323
Revolutions per minute 		1,412 ...	1,460	... 1,519
Electric horse-power required	274 ...	430	530
Pump efficiency percentage...	570 ...	72T	...	70’8

It will be seen that, by altering the periodicity of the
generating station by just over 7 per cent., which can
easily be achieved, the pumps can be made to give a wide
range of outputs. At the same time, it is clear that the
minimum output of 375 gallons comes very near the
maximum load with which any of the two alternators
can cope. It was therefore advisable to choose an
arrangement of motors that would throw the least
possible load on the remaining steam set in case the
other one were stopped for any reason. This necessi-
tated the subdivision of each motor-drive into two

Fig 4.—Sectional Elevation on Line C D of F1g. 1.

L

Figs. 1 to 4.—General Arrangement of Pump House.

300-horse power motors, one of which would be taking
the load, while the other one would be running idle in

such an emergency. The result has thus been achieved
that the motor efficiency at half and at full output of
the pump is the same—namely, 93 per cent.; whereas,
in the case of one 600-horse power motor, the efficiency

* From a paper read before the Midland Institute of
Mining, Civil and Mechanical Engineers.

at half-load would have been reduced to 89 per cent,
j The difference in the power factors is greater still, being
93 and 84 per cent, respectively. The two points
( combined make a difference of 11’7 per cent, in the
current carried by the remaining alternator, and this
I amply justifies the subdivision of the motors into two.

Another point gained by this arrangement is the reserve
created by the existence of two motors instead of one.
Figs. 1 to 4 show the general arrangement of the pump-
house.

It was decided to fix a system of ventilating vanes on
both rotors, and the result has been very satisfactory,