Compressed Air Work And Diving 1909

CHAPTER XI. Air Compressors. In tunnel and caisson work air will be requirecl at pressures up to 45 Ibs. per square inch or so for Alling the working section of the tunnel and working chamber of caisson. For working the rock drills and grouting, a pressure of about 100 Ibs. per square inch will be wantecl. For the lower pressures one-stage compression is usecl, but éibove 75 Ibs. two-stage compression will be more economical and is generally usecl. The ad van tages of two-stage decompression can be seen by consideration of the diagram (Fig. 16). The curve b, H shows the pressure and work done during compression up to 75 Ibs. pressure. The air taken into the cylinder at atmospheric pressure is compressed, following closely the line of adiabatic compression. Adiabatic compression takes place when air is compressed without parting with any of the heat acquired from the work done upon it during compression. Isothermal compression takes place when air is compressed and remains at the initial temperature. This can only happen when the air has time to part with the heat acquired by coming in contact with some colcler body. In the cylinder the air will part with some of the acquired heat by coming in contact with the water jacketecl cast-iron walls. But however perfeet the water jacketing may be,