The Horizontal Steam Turbine For Stationary Plants

Fig. 11. “Broken down" oil One source of water accumulation in the oil is the steam leakage of the giand packing (A3, Fig. 4). The steam blows past the packings into the housings of the main bear- ings (F2) and condenses. Water may also leak into the oil from the water cooling coils in the oil cooler (T6), or from the water jackets (K) in the housings of the main bearings. Where leakage of water into the oil system cannot be avoided, a water trap (Ti 1), fitted in a vertical position, to the bottom of the oil tank, has been found of great ser- vice. The water, circulating with the oil, will separate and drain into the trap. Once there, it cannot mix with the oil again. This water trap should be drained every twenty-four hours, letting the water and sludge run until clear oil appears. The drain cocks on the oil tanks should be opened be- fore starting up the turbine, and at least once every twenty-four hours to remove water and impurities. The suction of the oil pump should be from 2 to 4 inches above the bottom of the oil tanks, as otherwise any separated water will be taken up by the pump, the oil, and passed into the the unfavorable influence of water upon the oil, it is well to remove each clay, from the bottom of the oil tank., 3 to 6 gallons of oil for treatment in a steam-heated separating tank and later in a good filter. The purified oil should be returned to the circulating system at the same time that a corresponding quantity is drawn off for treat- ment. In this way the vitality of the oil can be maintained at a high standard. If the oil capacity of the system is small, it is particularly desirable to follow this treatment. It is good practice to have a large quantity of oil in circulation, with large oil tanks in churned with oil system. of which the oil has time to rest and separate from the air, water, dirt and other impurities it collects in the system. Broken Down Oil The length of service of an oil is dependent upon the quality of the oil. An unsuitable oil breaks down quickly and “goes to pieces” badly. The correct high-grade oil, under normal conditions, will give good service for 10,000 working hours at least; and under severe- and very unfavorable working condi- tions, for 3,000 working hours at most. Fig. 11 is a photograph of an actual sample of broken down oil. The original oil has separated -into three distinet bodies. At the top is clear oil; at the bottom is clear or somewhat cloudy water; between the two is a slimy mixture, a large portion of which is water intimately mixed with less than 5 per cent of oil. This slime represents the broken down oil and may be due to unsuitability, incorrect manufacture, or to some Chemical action on the oil in the service. Broken down oil accumulates in the most dangerous places, namely, the oil pipes which lead the oil from the distributing pipe (T1, Fig. 4) into the main bearings (F2). Partial stoppage of the pipes may result. Broken down oil also accumulates, as a slime, on the water cooling coils in the oil cooler, thereby decreasing the efficiency of the cooler. The circulating oil assumes a temperature higher than normal which, in extreme cases, greatly impairs the life of the oil. If broken down oil forms in the oil pipe leading to the governor, or inside of the governor gear, the governor may stick and fail to act. In consequence, the turbine either will gradually slow down or gradually inerease in speed mueh above the normal. The parts of the governor gear with which the oil comes in contact are very sensitive, and the oil must be absolutel y clean and of high quality to guarantee smooth working of the parts. Foreign Substances Because of the penetr ating and cleansing effeet of oil in a circulation system, every oil circulation system must be thoroughly cleaned after an initial run of 150 hours. 15