HELD AT THE ROYAL VICTORIA HOTEL, SHEFFIELD, APRIL 11TH, 1891. MR. JOSEPH MITCHELL, M. INST. C.E., F.G.S., PRESIDENT OF THE VISIT TO THE NUNNERY COLLIERY, SHEFFIELD.* The CHAIRMAN-I would first of all propose that the best thanks of the members of the Chesterfield and Midland Institutes be given to the Nunnery Colliery Company, and especially to Mr. Emerson Bainbridge, who has been at so much trouble, and has kindly imparted some very useful information. As we have in our hands printed particulars of what we were to see, and have made our visit, Mr. Bainbridge, I am assured, will be very pleased to answer any questions that members may wish to ask. Meanwhile I have great pleasure in proposing that our best thanks be given to Mr. Bainbridge for the trouble he has taken. Mr. JACKSON (President of the Chesterfield Institute)—I have great pleasure in recording on behalf of the Chesterfield engineers that we were much interested in everything we saw at the Nunnery Colliery, and as we are in a comparatively new district I hope some of our members may have seen something that it will be interesting to them to ask Mr. Bainbridge more questions upon. There is a great variety of machinery, and the plant is of a very substantial character. The resolution was carried unanimously. Mr. E. BAINBRIDGE said that as no questions were asked he took the opportunity of acknowledging the kind vote of thanks. It was possible that the information given on the slip handed to members that morning was sufficient to enable them to dispense with any further questions, but if anything should arise on which more information was wanted, he would be pleased at a future meeting, or by correspondence, to give it. It had been an especial pleasure to himself to have been the means of showing the party that day over the Nunnery Collieries, since he believed it was the first time the two Institutes had joined together for discussion. He hoped it would be the first of a series of useful meetings at which members might combine together for the purpose of discussing matters of mutual importance. * See description on page.237. DISCUSSION UPON MR. MAURICE DEACON'S PAPER ON "COMPARATIVE EXPERIMENTS UPON A CAPELL AND A SCHIELE FAN WORKING UNDER SIMILAR CONDITIONS." The CHAIRMAN-We will now take the discussion on Mr. Deacon's paper. Possibly he may have something to add before the discussion commences. Mr. DEACON had no additional remark to make, but would be glad to answer any questions. Mr. J. CRIGHTON wished to ask some questions. He thought it was well understood that in experiments upon fans on pits, the water-gauge should be taken in the fan drift. He believed that was finally settled by the North of England Institute some years ago, and that being so, he could not admit the statements made here to be right. In one case the Schiele fan appeared to have produced 43,699 cubic feet of air per minute with a water-gauge of 1 inch in the fan drift, and 45 down below at the separation doors; and in the next the Capell fan produced under the same conditions and on the same pit 60,084 cubic feet of air per minute with a watergauge of 1 inch in the fan drift and 7 below. How could that be, as it was impos sible to get that volume and keep the water-gauges the same if the latter were taken properly in the fan drift. In the next case, the Capell increased from 60,084 to 118,241 cubic feet, with a water-gauge of 3.25 in the fan drift and 18 in the pit. He (Mr. Crighton) said this could not be correct, for to increase to 118,000 there must be 2.7 water-gauge down below. The Schiele fan, tested under so-called similar conditions with the Capell-but the conditions were not similar-was a fan for 30,000 feet of air per minute, with a 3-inch water-gauge. It was like putting a child to do as much work as a man. It was impossible for that little fan to pass anything at all approaching the amount of air which the large Capell fan should pass. The only way to work under similar conditions would be to have fans of the same size, driven by engines of equal power, with a fan drift and every other condi tion similar, to take the water-gauge down below, and then to measure the air down below in the returns and close to the bottom of the upcast. Under these conditions he offered on behalf of the Schiele to arrange for a good test with the Capell anywhere; but with such conditions as those referred to in the paper, he could do nothing, because they were absurd. For one thing, the dissimilar conditions would force the Schiele to show a water-gauge of 4 inches to produce 1 inches in the pit, whereas the Capell, with a water-gauge of 3.25 inches, produced 18 inches in the pit, and used its high water-gauge for its useful effect. The correct place to take the water-gauge was at the top of the upcast opposite the fan drift. His own deduction was that Mr. Capell got 37 per cent. of useful effect with his large fan on that pit, and not 69 per cent. Professor LUPTON referred to a paper he had read before the Midland Institute in December, 1889, on a fan he had designed and designated "The Medium Fan" (see Transactions of the Federated Institution of Mining Engineers, pages 65-72, Vol. I.). Having communicated with the President and Secretary of the Midland Institute, he understood that he should be in order in coupling with remarks on Mr. Deacon's paper some observations upon his own, the discussion on which had not been closed. The Medium fan that had been constructed from his designs was 20 feet diameter, and was put up to give 40,000 cubic feet of air per minute; actually it was producing 60,000 feet. In observing such fans as those of Mr. Capell and Mr. Schiele, he had considered that the entrance orifice was restricted, causing an appearance of high water-gauge in the drift immediately adjoining the fan, which high watergauge was not actually realized in the pit. Therefore he made the entrance to the Medium fan of such a size that there should be no constriction of air either in the entrance or discharge from the fan, to cause undue friction, and to raise the water gauge unduly. Mr. Deacon's paper was one of the most useful and instructive papers ever put before the Institute. He would venture to suggest that it was sometimes difficult to make accurate experiments, even with the best intentions, and he thought this paper showed that difficulty. The preceding speaker said some of the results obtained were impossible. He (Professor Lupton) did not agree with him there. He did not think they were perfectly theoretically consistent one with another, but that was the case with all experiments which were not cooked. The fact that they were inconsistent showed that they were given by an engineer who recorded what he had found, and left inconsistencies open for criticism. Having said that, he should like to point out that the water-gauge, as indicated at the fan drift and the doors at the bottom, showed a remarkable amount of shaft friction, to say the least of it. He had calculated what the shaft friction should be for the depths and size given, and allowing for a considerable length of roadway, he estimated the shaft friction at a maximum, with the air going at 120,000 feet per minute, at about 66 or two-thirds of an inch water-gauge. If, in the case of the volume of 122,012 feet of air, with two inches of water-gauge at the separation doors at the pit bottom, 66 were added, the theoretical water-gauge in the fan drift became 2.66 inches, instead of 3.85 inches as given in the paper. What had become of the difference? No doubt when Mr. Deacon replied it might be accounted for. But supposing it could not be accounted for except on the theory that the constriction of the fan orifice gave an apparent water-gauge at the fan which did not exist in the mine, the effective work would be reduced by one-third. The efficiency, instead of being 74 per cent., would be reduced to about 50 per cent; for substituting 66 shaft friction for 1.85, the efficiency was brought down to 50 per cent., which was a very good efficiency. No mine owner would complain of that percentage efficiency, but he thought if the air-way in the fan were enlarged, there would be a larger efficiency. With regard to the Schiele fan, there could be no doubt that the air was knocked about somewhat unduly; and whether it were called re-entry or otherwise described, there was doubtless a certain amount of power wasted. The Schiele fan as a rule had a restricted entrance, causing loss of power in the fan, in a similar way to what happens in the Capell fan (with the result in the case of the Capell fan that the fan water-gauge was so much higher than the water-gauge at the separation doors). But the Capell fan water-gauge at the highest was not a high water-gauge. Taking the speed of the periphery of the fan, and calculating the theoretical water-gauge, it would be found that the actual water-gauge was 10 per cent. less than the theoretical waterguage. In the Guibal fan, which Mr. Robert Howe had so thoroughly described, the actual water-gauge was from 20 per cent. to 30 per cent. higher than the theoretical water-gauge, according to the way in which it was worked, and according to the quantity of air passing through. He did not mention that as necessarily giving high useful effect, but as giving a high water-gauge. There might, however, be a high useful effect with a low water-gauge, and vice versâ. Mr. G. M. CAPELL wished to disclaim having anything to do with these comparative experiments with the Capell and Schiele fans. They were made, and after they were made he heard of them, but had absolutely nothing to do with them more than seeing the results after they were taken. Mr. Deacon would corroborate that statement. Professor Lupton had remarked that the entrance to the Capell fan was restricted. The Capell fan was 12 feet 6 inches diameter, and the inlet 7 feet 6 inches. Would Professor Lupton state the size of the inlet of his 20-feet fan? Professor LUPTON-7 feet. Mr. G. M. CAPELL-If the Capell fan inlet was 7 feet 6 inches to a 12 feet 6 inch fan, against 7 feet to a 20 feet Medium fan, he considered the former inlet had much less restriction. He prided himself that the Capell fan had no restriction of inlet or exit. The air passed through the port-holes in the cylinder, which were carefully regulated and larger than the size of the inlet. As Mr. Herbst, engineering professor of the Mining School of Bochum had said, "There is no restriction in the Capell fan, though at first sight it might appear so to those who have not studied the question, the port-holes in the cylinder being larger in area than the inlet." That, he (Mr. Capell) considered, was the reason why the Capell fan was able to pass larger volumes of air, at high gauge, than any fan of the same size with which he had hitherto been acquainted. In this opinion he was entirely corroborated by experiments made in Germany, where he had a fan 12 feet 6 inches in diameter; and where, he might be allowed to add, he should shortly have two more running, which were to give 127,000 cubic feet on test, and 10-70 inches water-gauge. That did not look as if restriction at the inlet of the Capell fan had any material effect. Gauges in Germany were taken a long way off in the passages of the mine, more than 100 feet from the exit of the fan. He agreed that the question where the gauge should be put required careful consideration. He understood that the gauges in the recent experiments, made by the Fan Commission in England, had been taken 6 feet from = = = the entrance to the fan inlet. In Germany it was not so, and there the gauge tube was placed at right angles to the air-current. In the five experiments made by Mr. Herbst, reporting engineer of the Prussian Fire-damp Commission, and professor of engineering at the Bochum Mining School, he insisted on having the gauge pipe ground up to knife edge, in order to prevent any air eddying round the pipe edge, and so interfering with the water-gauge. As to the theoretical gauge, Mr. Lupton used h V2÷2g or V2÷644, h representing the height of the column of air which was raised by the centrifugal force or velocity of the blade tips of the fan.* This formula had been abandoned on the Continent, in France, Belgium, and Germany. It was not h V 2g but h Vag, and the theoretical gauge was now double what was formerly used.† All the gauges stated to-day had been worked on the double theoretical gauge and not on the single theoretical gauge. The proportion of actual to theoretical had been calculated on double the amount of theoretical gauge to which Mr. Lupton alluded. With regard to the gauge on a mine being invariable (the quantity of air that could be passed at a given gauge on the mine being invariably the same with every fan) he had stated five years ago his conviction, from experiments, that such was not the case; that fans had local power of creating gauge, and that the local power of creating gauge was different in different fans, and some fans had the power of throwing their gauge farther back into the mine than others. About that he had not the smallest possible doubt, from experience, with many fans in Germany, Capell and Guibal fans, working side by side, and certain results before the meeting to-day. That conclusion was further corroborated by Mr. Longden's statement, that on his own fan he found the same thing, namely, an entire discrepancy between the observed gauge required at the fan drift, to get the same quantity of air as had been previously got by the furnace. On such an occasion as this it could not be out of place to go back some years on this subject. In 1884, being then very young in the matter of fan experiments, he succeeded in getting a trial in a colliery at Cradley, between a very small open fan, made for mine experiments, and a 16-feet Guibal fan. It was at Homer Hill Colliery-the results were published, and the writers in the Colliery Guardian plainly said it was nonsense. The observations were taken by Mr. J. E. Swindell, and recorded in his (Mr. Swindell's) book. The mine was blocked to bring its capacity somewhere near that of the small fan. At 1-inch gauge the Capeli fan passed 14,128 cubic feet of air; the Guibal at 14-inch 14,508 feet of air. The Guibal fan, at 1-inch water-gauge, passed 11,412 feet, so that practically the Guibal fan took 14-inch gauge to do what the little Capell fan did at 1-inch gauge. At Tamworth Colliery a Capell fan had now been working several years. It was constructed to meet the state of things in that pit. The furnace gave 10,125 feet of air with 75 inch water-gauge. The Capell fan was then put on the pit, the air and water-gauge were taken at the same place, and Mr Ridsdale stated * To reduce this to inches of water-gauge multiply by 00012 × 12. The fans can only show a percentage of the new theoretical gauge which they can never reach. EE |