Document X7vEnXBvmZwMwnLdz2YZLe6XG

f l 1*. \ 1' Actuol size of Ihe five most popular V-beh cross' sections tests and hove been found satisfactory In service. Minimum A, 8, C, D ond E. These sizes were determined after many sheave dlometert for these belts ore given in Table l( p 125 duces Internal friction end beau For the five popular belt sizes. A, B, C, D end E, minimum sheave diameters can be recommended. Table I gives these sites, determined after many tests and found satisfactory in service. 'Laboratory-tests and practical expert* ence show reasonable belt life tan be expected with sheaves as small as the recommended minimum. -If possible, it is even better to use sheaves somewhat larger than the minimum. Doing a 9.0*ln. or 8.6-b. sheave with a C sec tion belt, for instance, is not tbe differ ence between success or failure of the drive. <But a 10.6-in. instead o! an 8.6-to. sheave docs make a great difference is the belt's life. If belts on on 8.6-in. sheave have a 2-year life, It is not un usual with a 10.6-in. sheave for the same drive to have a belt life of 4 years or more. So consider replacement costs when installing a V4ell drive. Largcr-diam* eter sheaves may cost more, but life la longer ond belts are not replaced nearly so often. Cost of replacing one set ol belts usually offsets the difference in cost of the slightly larger sheaves. To under-design a drive that is used any length of time is poor economy. Bolt Speed. Maximum diameter of sheaves osed on a drive is governed by (1) space limits and (2) belt speed. The first condition requires little ex planation. If spoeo does not permit as large a diameter sheave as desired, the only thing to do is to use a smaller one with grooves for enough belts to drive the load safely. Belt speed requires a more detailed explanation. Between practical limits, the larger the diam eter of the driving sheave, the greeter the belt speed and the more horsepower eaeh belt on the drive transmits. For greatest efficiency, belli must travel neither too fast nor too slow. What are these practical limits that govern selec tion of proper speed? Horsepower rat ing tables In V-belt manufacturers' cat alogs show e recommended speed of 1000 to 5000 ft per min, depending on the diameter of the driving sheave. There is a reason for these limits on peed. A belt at slow speed transmits less horsepower than one traveling faster. So the drive as o whole requires more belts when speed is low. Since the power rating of a belt drops of! rapidly at speeds below 1000 ft per min, it is not economics) to go below this point on most drives. An equally good reason exists for limiting top belt speed. As speed ap proaches and exceeds 5000 ft per min, centrifugal force tends to stretch bells and throw them away from the groove. Thus, the effective arc of contact on the sheaves Is reduced. Another con sideration in speed Is safety. Most castiron sheaves are constructed'to with* stand safely a rim speed net In excess of 5000 ft per min. While special drives are sometimes constructed for use at lower or higher speeds, it is best to observe the recommended limits (or the overage drive. Are ol Contact. Arc of contact on sheaves must be considered when se lecting an adequate drive. Horsepower ratings for different-sited V-belts art based on a 180-deg sre of cootact. This are depends on the difference in sheave diameters and the distance between shaft centers. -If one sheave is smaller than the other, it has leas than 180-deg arc of contact. The smaller the sre of contact, the greater the number of belts required (or o given drive. Base V-belt-drive selection on the prime-mover ond load characteristics si well as on required horsepower and belt speed. Do not select size and oddber of belts for a drive on the basis of the prime mover's nameplate boro power alone. Considerably more power is often needed to start a load then to drive it at normal speed. It makes a difference whether the driving unit Is a squirrel-cage motor with high etarting torque, a dc motor with comparatively low storting torque, or a gasoline or diesel engine with poi nting characteristics. Similarly, the load thrown on tho drive depends oo (Continued on page 160) TABU II--RECOMMENDEO CROSS SECTIONS OF V-BELTS FOR DIFFERENT MOTOR HORSEPOWERS AND SPEEDS tsoo itoo aoo AAA ..A A A And A , 0 A or 6 Ae And A aS A B A0 S mdno A*B- e 0c to. IS. BC C ttso.. cc so. c .40 (aD CaD CnD O ssoo.. C or D C or O CorO CorO O O O O vs. C or D CorO OorE too. O D O or E US........... ISO........... too........... fSO (adore. O O O or C Dor 6 D D E E DOC E Notfi Wta fcM b*0 Motion* i Arena 0 i)>mh pitell dUnrli Italltd* Aom Itn tdta art Oeritod, om At WS mcUm. 0 ap iMUtlre. * i ewtrefal dWo. . 914 DorC Owl 126 (768) POWER 0c.mb.< IM* London Plans First Oil-Fired Central Station in Britain New Bankiide Generating Station will have flue-duet removal equipment that will also remove eulphur compounds by wathing. Ultimate plant will have (our 60,000-kw turbine-generator. By H J RANDALL, Managing Olrtctor, London flottrit Lighting Co * For over 58 years s generating its- indefinite postponement, so the elation \ tioo has stood on the Thames River in was operated despite much damage { the heart of London, opposite Si. Pout's from enemy bombing. Cathedral. More than three centuries In 1945 when rebuilding was again *|o this Bsubside district was London's decided upon, there was wide public cultural and recreational center, but it interest in town planning and smoke long since been industrialized. abatement. The London City Council, When a power plant was erected, el- which produced a plan for new develop most on the Clobe Theatre site where ment of bombed areas, scheduled the Shakespeare's plays had been produced, Bankside district for offices, light in Ihtte thought was given to town plan- dustries ond buildings for cultural pur ) "fag, architectural beauty and smoke poses. The station owners decided that hatemenL the new plant should be worthy of the The station, designed for efficient op- rebuilt London. Thoy commissioned (ration at minimum cost, was a feature Sir Gilbert Scott to design tho building. f engineering interest for visitors to Although tho architect's design was ad London. In course of time it beeame, mirable much opposition arose to re b*elete, and in 1939 it was decided to building the station on its present site. '(build. But World War 11 caused an The government settled the question by deciding that because of acute shortage of generating capacity and scarcity of sites in London the station should be rebuilt at the seme location. It was stipulated, however, that oil should be used instead of coot Hc^ce, Bankside will become tho first oil-fired station in Britain and the first of its kind fn tho world designed to prevent emission of flue gas with a high sulphur content. Building. The new building will be about 230 ft behind and patallel to tho river bulkhead so apace will be ample for o planned riverside boulevard. Foundation will be built on Lxmdon blue cloy about 34 ft below grade. Water-bearing ballast and tilt overlie the cloy, ond the building area will be dammed off by steel sheet piles. Wherever- possible the circulating water tunnels will he deep enough to bo driven into the clay, but some com pressed air tunneling will be unavoid able. A river jetty will accommodate oil tankers and barges. Fuel will be pumped ashore through pip* in * tun nel between station and jetty. Terbino-Geaetotor*. The 240,000-kw ultimate station capacity will be made [j. 'OWEft December 1940 (789) 127