Compressed Air Work And Diving 1909

WATER CO O UNG. 109 There is another reason, however, why the air must not be allowed to attain too high a temperature in the cylinders. That is this. Too high a temperature is clestructive of lubricants, and if these are of a common low-grade quality, they are soon burnt into gritty or gum- like substance, and if the temperature is raised above the flash-point of the oil, there is the danger of an explosion or ignition in the compressor or air receiver. Such an occurrence in an air receiver would be highly dangerous, as it might happen without wrecking the receiver, and the smoke generated, if it happened with the low-pressure receiver, would be driven into the working section of tunnel, or working chamber of caisson, and endanger the lives of the workers. When water is cheap, it is an advantage to have water-cooling before admitting to the air cylinder. This should be followed by intercooling, in the case of two- stage compression, and then by after-cooling. This after-cooling in the low-pressure mains is useful in keeping the temperature at a point comfortable for the workers. By drying the air it also helps to prevent moisture being cleposited which would cause them to get frozen up in severe weather. This will not, how- ever, get rid of all the moisture, and drip valves should be fitted at any low point to allow any moisture cleposited to be withdrawn. These also are, however. liable to set frozen up if not protected, so that there is a distinet advantage in having dry air. This also applies to the high-pressure mains. The fali in pressure due to expansion may also cause the exhaust of clrills and other engines to get frozen up if the air contains mueh moisture. Whether the air taken in is water-cooled or not, it should always be drawn in from outsicle the engine-