328 THE COLLIERY GUARDIAN. February 12; 1915. across the settling sump to the overflow launders, where it trickles over the edge and flows through the arteries into a central launder, and thence into the main sump. The total length of lip launder in each settling sump is approximately 150 lineal feet, which gives complete settlement. The water is neutralised with carbonate of soda, the cost of treatment being approximately 2*6d. per 1,000 galls, pumped. A log book is used in the pump station in which hourly records are kept of the state of the water and of the percentage acidity. The capacity of each settling sump is 26,500 galls., and each of the two main sumps is 148 ft. long by 25 ft. wide by approximately 8 ft. deep, containing approxi- mately 185,000 galls.; taking the average quantity from the mine as 10,000,000 galls, per month, this gives for each main sump a storage capacity of 13j hours, which is ample for repairs or replacement in the plant should such an emergency arise. All drain pipes, overflow pipes, test cocks, &c., are led to large open funnels which in turn are connected to the sump by large pipes. This ensures an entire ELEVATION Fig. 5.—Sumps and Pump Chamber. absence of water splashing about the plant and floor. The pump station and suction sump are shown in fig. 7. The plant was started on September 15, 1913, and as connections were made on the 12tb level, so the other pumps were gradually shut down until in December, 1913, the two centrifugal pumps were handling the whole of the water of the mine. The total pumping costs since the new plant has been in operation, viz., October 1, 1913, to September 30, 1914, are at the rate of 2s. 8d. per 1,000 galls. The pumping costs with the old plant from January 1, 1913, to September 30, 1913, were at the rate of 4s. 2d. per 1,000 galls., showing a net saving of £750 per month based on an average water duty of 10,000,000 galls, per month. While these figures give the direct saving to the mine, yet they do not give the actual costs of operating the centrifugal pumps, as there are are six large air ELEVATION PLAN pipc Fig. 6.—Settling Sump Details. pumps below the 12th level, the costs of which for spares, power, maintenance, &c., are included in the above figures. Costs. Since the new plant started, a complete record has been kept of the costs, and the following figures may be of interest:— Total cost of spare parts purchased from makers, excluding co>t of parts made by « mine (which are charged in workshop costs given below) ................... £103 14 4 In addition to these costs there are the costs incurred in the workshops on the plant :— Total workshop costs on pumping plant, September 15, 1913, to Sep- tember 15, 1911 .................... 76 2 0 Total costs of spare parts purchased as shown in table, plus workshop Costs... 179 17 4 Total galls, pumped from September 15, 1913, to September 15, 1914 ........ 111,650,000 Cost of workshopsand spare parts.... 0*385 pence per 1,000 galls. Complete tests have been made by the mine and head office staffs to determine whether the guaranteed figure had been complied with. The first test was made on November 12,1913, and on October 29, 1914, practically one year afterwards, a further test was carried out to determine how much the plant had fallen oft in efficiency. The results of these two tests are as follow:— Guaran- teed First tests. 12/11/13. (2) . 2,520 .. Se ond tests. 29/10/14. (3) .. 2,549 Head in feet figure. (1) 2,490 .. Gallons per minute 375 .. .. 449 .. .. 406*5 Input horse-power into motors (integrating watt-meter readings 4- time) . . 573 .. . 538*5 Horse-power input into pumps, based on 92 per cent, motor efficiency ■ 527 .. .. 495 Average efficiency of pump (per cent.) 62 .. 65 .. 63*4 Overall efficiency of pump and motor (per cent.) 57 . 59*8. 58*3 Note.—(1) At the first and second tests of the pumping1 plant the two units gave such close agreement in results that the figures shown in columns (2) and (3) of the above table are the averages of the tests on the two pumps. (2) The efficiency of the motors as given by the tests at the makers'’ works is 95 per cent., and this would bring the actual efficiency of the pumps at the first test down to approximately 63 per cent., but for the purposes of this paper only the over-all efficiencies of the combined units are dealt with. SUMP Fig. 7.—Pump Chamber. MAIN SUMP MAIN SUMP SUCTION SUCTION SUMP f I j _ v Fig. 8.—Pump Chamber (2,000 gallons per minute). Comparison of centrifugal and ram pumps. The principal point in the table of tests is, of course, the efficiency of the complete , unit, i.e., net electric units input, compared to net water output in equivalent horse-power, or to put it into hard cash, what is the cost of power for pumping by centrifugal pumps. Careful records have been kept of the actual metered units into the pumps and the water quantities delivered at the collar of the shaft. These figures show that during the last seven months 0*611 unit of electric power was required to lift 1,000 galls, through 100ft., or taking the cost of the unit as 0*525d., the net cost of power is 0*321d. per 1,000 galls, per 100 ft. lift. An independent test was made on December 6 last year to obtain these figures, and the result showed that the pumps used 0 623 unit per l,0(J0 galls, per 100 ft. lift. There were certain valid reasons why centrifugal pumps were installed at the Durban Roodepoort Deep instead of reciprocating pumps, and it may be of interest briefly to state these reasons. (1) Initial Cost.—The capital cost of a centrifugal pumping plant, complete with motor, starter and com- bined bedplate, all delivered in Johannesburg,, is approximately 60 per cent, of the cost of a reciprocating pumping plant, assuming conditions similar to those at Durban Deep, which calls for 800 galls, per minute against 2,500 ft. head. For a 2,000 galls, per minute plant against 2,250 ft. head, the centrifugal pumping equipment becomes 40 per cent, of the cost of reciprocating pump equipment. (2) Weight of Plant.—The centrifugal equipment weighs approximately 70 lb. per gall, of water pumped per minute. A reciprocating equipment would weigh approximately 350 lb. per gall, per minute. (3) Reliability.—This was an unknown figure when the pumps were installed, but the authors were of the opinion that, in spite of a very considerable amount of hostile criticism, the centrifugal pump had not had fair treatment, and the results of a year’s run have confirmed their opinion, as there has been no trouble of any sort experienced with the pumps since they were installed. (4) Cost of Maintenance.—This also was an unknown figure, and here again the authors believed that with clean water the maintenance costs could be reduced to a reasonable minimum. The actual figures are given in the early portion of this paper. (5) Cost of Excavations for Pump Chamber.—The larger the quantity of water to be handled the bigger the proportional saving by using centrifugal pumps. For a 2,000 galls, per minute plant the excavation for a centrifugal equipment would be approximately 10 per cent, of the cost of excavations for reciprocating equip- ment. Fig. 8 shows the comparative sizes of pump chamber for centrifugal and reciprocating pumps based on a net capacity of plant of 2,000 galls, per minute. The above are the general points which appeal to the authors as indicating the merits of centrifugal pumps for high lifts, and after a year’s experience with the particular plant under discussion there are other favourable features evident which cannot be assessed in cash or figures, such as (1) simplicity of repairs and replacements, (2) smoothness of running, (3) minimum of attention required during operation, and other points which are beyond the scope of this paper. During the last few months important extensions