450 



KEPORT 1889. 



The general system of working is illustrated roughly by the sketch 

 diagrara (Fig. 1), which of course is in no way drawn to scale, and it is as 

 follows : — The steam cylinders (I.) compress the air to a pressure of five 

 atmospheres (six atmospheres absolute) or thereabouts in the compressor 

 cylinders (II.) The air is drawn in direct from the engine-house, where I 

 found it to be about 70° Fahr., and after it has finally passed along the 

 mains for some little distance it is again about the same temperature. It 

 is therefore of the greatest importance to prevent its temperature rising 

 during the compression, as all heat so taken up by the air represents 

 work done in the steam cylinders of which no part whatever can be 

 utilised. If the air were compressed adiabatically, i.e. without any cool- 

 ing whatever, its temperature on leaving the compressor would be about 

 430° Fahr. — a temperature higher than that of saturated steam of 300 lbs. 

 per square inch pressure. At St. Fargeau water for cooling is allowed 

 to run into the cylinders through the suction valve during the suction 

 stroke in such quantity that the final temperature is only 150° Fahr. 

 So far the result is satisfactory enough ; but owing, unfortunately, to the 

 particular way in which the cooling water is utilised mechanically, the 

 air does not get cooled until after it has been compressed, so that 

 practically no benefit is obtained from the cooling in spite of the extent 



9B63.A 



to which it occurs. The power expended, as we shall see presently, is 

 practically equal to what would have been expended had the compression 

 been adiabatic. The quantity of air dealt with at each revolution is 

 47-6 cubic feet (for the pair of double-acting compressing cylinders), 

 which is equivalent to 3-55 lbs., the quantity of water used being 

 about 2-4 lbs. 



After compression, the air, now having an absolute pressure of six 

 atmospheres and a temperature of 150° Fahr., is pushed into large boiler- 

 plate receivers (III-)) of which some are arranged to act as separators, 

 and in these a large portion of the cooling water, which has been carried 

 along mechanically by the air, is deposited and removed before the air 

 enters the mains (IV.) The principal main is 300 mm. (ll'S in.) in 

 diameter and about f in. thick. It is of cast-iron, made in lengths 

 perfectly plain at each end, and connected by a very simple external 

 joint made air-tight by indiarubber packing- rings. This joint leaves 

 the pipe quite free endwise, and also allows all necessary sideway freedom, 

 so that accidental distortion to a quite measurable extent is entirely with- 

 out effect on the tightness of the joint. The mains are partly laid under 



