Compressed Air Work And Diving 1909

I IO COMPRESSED AIR WORK. rooms, as the difference in temperature, éspecially in winter, will give a great increase in power. This is important also from the point of view of the health of the workers, as the air will then be much freer from clust and other impurities. In general arrangement the compressors of the leading makers are very similar. For two-stage com- pression the duplex type is favoured. In this type of machine there are two air cylinders and two steam cylinders, and these form practically two machines side by side. The low-pressure steam compresses the low- pressure air, and the high-pressure steam compresses the high-pressure air. Each pair of cylinders are connectecl together by one long piston rod giving- a tandem drive. This is the method adopted by Messrs Walker Bros, and Messrs Fraser & Chalmers for their most modern machines. The Ingersoll-Rand Co. also favour this type, but manufacture a large number of tandem drive machines, that is to say, machines with three or four cylinders on one long piston rod, three cylinders when air alone or steam alone are to be compounded, and four cylinders when both are to be compounded. The duplex arrangement is equally suitable for com- pounding either air or steam only. For tunnel work where most of the air required will be at a low pressure, the steam only will be required to be compounded. The compressors usecl at the Greenwich Footway Tunnel were on this principle, and were made up as follows:—Steam cylinder H.P. 18 in. diameter, L.P. 30 in. diameter, and two air cylinders 24 in. diameter. Length of stroke, 3 ft. 6 in. These engines were manu- factured by Messrs Walker Bros., and suppliecl by them