The Horizontal Steam Turbine For Stationary Plants 1920

gear. Usually, however, in a direct pressure feed system, only one pump is employed and this pump must deliver all the oil under sufficiently high pressure to work the gover- nor gear. If, for any reason, the oil pressure fails be- low that required, a piston in the go vemor gear, held up by the oil pressure, falis and causes the steam supply to be shut off. The turbine will usually come to a stop before the oil supply to the bearing is sufficiently reduced to cause damage. Where an elevated tank is employed, sufficient oil is usually assured to lubricate the turbine for at least thirty minutes, should the oil pump fail to work. When starting up a turbine, where there is no elevated tank, the oil supply to the bearings will not be adequate until the tur- Fig. i o. Ring oiled turbine bearings bine is running at about one-quarter normal speed. Therefore, before starting up a turbine, it is necessary to apply oil to the bearings by means of a hånd or an auxiliary power-driven oil pump. An auxiliary steam-driven or electrically- operated oil pump is employed for large turbines. As soon as the turbine reaches normal speed the auxiliary oil supply should be cut off, after which the oil pump, auto- matically operated by the turbine, will supply the requisite quantity of oil. Ring Oiled Bearings (Fig. 10) The bearings (F2) have oil reservoirs (F3) from which the rings (F4) suspended on the shaft (F) continuously carry oil to the shaft, distributing it through a longitudinal groove over the entire bearing surfaces. The oil, as it leaves the ends of the bearings, drops back into the oil reservoir. Occasionally the bearings (F2) are fitted with Sight Feed Drop Oilers, which feed a certain number of drops per minute into the bearings. In such cases the oil, when leav- ing the bearings, is caught in "sa ve-al Is,” filtered and used again. This system, however, is obsolete and has been superseded by the ring-oiled bearings, which are now generally used on small tur- bines. OIL Oil Qualifications Correct high grade oils, specially manufac- tured for turbine lubrication, are least af- fected by the presence of air, water and other impurities. The use of the correct oil will eliminate wear and manifest efficient lubrication in terms of low bearing temperatures. With an incorrect grade of oil, the bearing temperatures are always extremely high. The rate of oil oxidization—generated by the great heat—is thus increased, so that fre- quently the life of an ordinary oil in a tur- bine is only a few months. Circulation oils have been specially treated to produce ready separation, and to with- stand contamination with impurities under the severe conditions of continued service. When the operating conditions are extreme and impurities collect in the system, the oil in its circulation conducts to the journals and bearing metals those impurities, which may cause their corrosion. The most prominent failures of oil in cir- culation systems have been in turbines where the surface speed of the journals was high, the oil circulation rapid, with a practical cer- tainty of water collecting in the system and 12