known to be in excellent condition. Comparisons of this kind, while not scientifically exact, are perhaps of greater interest as a measure of commercial performance. The data at hand of test on one of the 400 K. W. turbines at Wilmerding shows a result of 16.4 lbs. per electrical horse power hour at full load, with 125 lbs. steam pressure and 26 to 27 inches vacuum. At half load it is 18.2 lbs. At the Elberfeld Municipal Electricity Supply Works in Germany, two 1,500 horse power Parsons turbines, which are run in parallel with two Sulzer horizontal engines, were tested by Prof. Schroter, Dr. Weber and Mr. Lindley. With steam pressure averaging 95 lbs.. running condensing, and with 18.3 degrees of superheat, the result obtained, at maximum load, was 19 lbs. per K. W. hour; or about 11.4 lbs. per I. H. P. hour. Many other results have been recorded, but those given will probably be sufficient to show that under service conditions, the turbine has demonstrated its high efficiency. But is its efficiency maintained? A question often asked, and a very important one, too. Looking at the turbine casually, it seems as though there would be little opportunity for any change in its mechanical functions. There is no complicated valve gear to get out of adjustment; no pistons to leak; no rubbing surfaces to set up excessive friction; little chance of misalignment; and altogether there seems to be no good reason why its original condition should ever be very much disturbed. The blades appear to be the vulnerable point, for they do the work, and there are a good many of them. Their number, though, is in their favor, and being loaded as they are to only about 21⁄2 per cent of the pressure they are built for, they possess an abnormally large factor of safety. The experience has been that the turbine is less liable to depart from its original standard of performance than any other type of prime mover, and there seems little reason to suppose that it is capable of much deterioration. A recent interesting investigation along this line was made at the plant of the Cambridge Electric Supply Co., Limited, in England, where they have a 500 K. W. Parsons turbine. The outfit was erected in January, 1900, and during the past year has been doing very constant work. After it had operated about eight months, a second one was installed. The first outfit had been tested at the maker's works before shipment and showed a result of 24.1 lbs. of steam per K. W. hour at 526.4 K. W. And it was for the purpose of noting its performoperation that Prof. Ewing conducted recently a second test. * In this latter test the turbine at 518 K. W., under ance after a year's *London Engineering, June 14, 1901. nearly equal conditions of steam pressure and vacuum, gave a result of 25.0 lbs., and at 586 K. W., 24.4 lbs. In the second instance the turbine, besides trouble experienced with wet steam, was driving its own air and circulating pump (a surface condenser being used), and the steam required to drive these auxiliaries was charged to it. In the test at the builders' works, the turbine did not drive its pumps. The results, to use Prof. Ewing's words, give most satisfactory evidence that the turbine retains its character as a highly efficient generator. It remains to be said in this general connection that there will be found in steam turbine practice a more satisfactory treatment of the economy question than has heretofore prevailed. There will exist not only a truer basis of measurement than the indicated horse power, but there will be opportunity for more thorough demonstration. It is now generally recognized that efficiency guarantees on large engines have little significance. The builder is physically unable to completely assemble and test such engines before shipment, and the user is seldom able or disposed to incur the distraction and expense which a field test involves. It is in the exceptional case, therefore, that actual tests are made, and there is still much to be known concerning the economy performance of large engines. It might be said too, that while builders and engineers generally recognize the elements of design that conduce to efficiency, there is no unanimity of opinion as to what those elements will actually produce. It is, therefore, gratifying to know that one builder, the Westinghouse Company, is now erecting a new testing room in which a complete plant of boilers, condensing and superheating apparatus will afford facilities for testing turbines up to 3,000 horse power, at all loads up to full capacity, and larger units up to this point, with practically any steam pressure and wide ranges of vacuum and superheat. Thus, the conditions to be met in practice may be approximated in the shop, and the information acquired will be of the highest value. Turning now to one notable feature of the turbine-its compactness-Fig. 6 is a graphic illustration of the floor space it occupies compared with the vertical and horizontal cross-compound Corliss cngines, the basis of comparison being a 1,000 K. W. unit, including the direct-connected generator, the engine cylinders being 28 inches and 55 inches by 48 inches stroke, which, at 95 revolutions, with 25 lbs., mean effective pressure referred to low pressure cylinder, gives about 1,400 indicated horse power. It will be seen that the floor area of the turbine is about two-thirds that of the vertical engine and about two-fifths of the horizontal. Such comparison, of course, is limited in its application. With each set of conditions requiring special treatment, no standardization of space requirements can be established. Still, with the limitation of isolated experiences, it is possible without attempting to establish any universal laws, to make some reasonably close comparisons of the space required for the turbine as against the conventional types of engines. It has been thought desirable, then, to take a number of different-sized plants, each composed of several appropriate-sized units, the selections being as follows: 1,000 horse power in 3,000 horse power in 5,000 horse power in *10,000 horse power in 15,000 horse power in 30,000 horse power in 50,000 horse power in 2- 400 kilowatt units. 75,000 horse power in 10-5,000 kilowatt units. These combinations were laid out for the turbines, and for the vertical and horizontal cross-compound Corliss engines, all with their directconnected generators. A clearance space of 7 feet in all directions was allowed, and is probably a fair average. The computations were confined to the units themselves, with the clearance stated; the disposition of the balance of the plant being assumed to be unaffected by the type of motive power. Fig. 7 shows the comparison of floor space. The curves show the turbine to require about 80 per cent of the space needed for the vertical, and not over 40 per cent of that wanted for the horizontal. In this diagram the vertical engine compares less unfavorably with the turbine than might generally be supposed, while the horizontal engine curve is about where one would expect to find it. The latter is not carried beyond 10,000 horse power. this type of engine being practically limited in size to that required for the 1,500 kilowatt generator. Fig. 8, showing the cubic yards of foundation material required, is at the same time a more exact and striking comparison. The turbine would appear more advantageously still if the actual foundations needed for stability had been computed. Instead, the foundations in all three cases were figured at 15 feet depth to give space underneath engine-room floor for condensers, etc., though for large engines this depth is usually inadequate. The only foundation needed for the turbine is that necessary to hold its weight, as though it were a tank, or some other stationary affair. It does not even require foundation bolts, there being no vertical or horizontal thrusts to be resisted. Com *In this size the horizontal engine is figured on 5-1,500 kilowatt units. |