. Applied thermodynamics for engineers. by a pipe. The efficiency, as compared with that theoretically possible inisothermal compression, is to , some air being always carried away insolution. The initial cost is high, and the system can be installed only wherea head of water is available. Figure 90 illustrates the device (15). The head ofwater must be at least equal to that corresponding to the pressure of air. The cycle of this type of compressor may be regarded as made up of twoconstant pressure paths and an isothermal, there being no clearance and no valvefriction. 242. Details of
. Applied thermodynamics for engineers. by a pipe. The efficiency, as compared with that theoretically possible inisothermal compression, is to , some air being always carried away insolution. The initial cost is high, and the system can be installed only wherea head of water is available. Figure 90 illustrates the device (15). The head ofwater must be at least equal to that corresponding to the pressure of air. The cycle of this type of compressor may be regarded as made up of twoconstant pressure paths and an isothermal, there being no clearance and no valvefriction. 242. Details of Construction. The standard form of cylinderioY large machinesis a two-piece casting, the working barrel being separate from the jacket, so thatthe former may be a good wearing metal and may be quite readily to the jacket space is provided through bolt holes. On the smaller compressors, the poppet type of valve is frequently used for bothinlet and discharge (Fig. 91). It is usually considered best to place these valves. Fig. 91. Art. 242. — Compressor Cylinder with Poppet Valves.(Clayton Air Compressor Works.) in the head, thus decreasing the clearance. They are satisfactory valves for aito-matically controlling the point of discharge, excepting that they are occasionally 138 APPLIED THERMODYNAMICS noisy and uncertain in closing, and if the springs are made stiff for tightness, a con-siderable amount of power may be consumed in opening the valves. Poppet valveswork poorly at very low pressures, and are not generally used for controlling the intakeof air. Some form of mechanically operated valve is preferably employed, such as thesemi-rocking type of Fig. 92, located at the bottom of the cylinder, which has poppetvalves for the discharge at the top. For large units, Corliss inlet valves are usually employed, these beingrocking cylindrical valvesrunning crosswise. As insteam engines, they are sodriven from an eccentricand wrist plate as to giverapid ox^ening an
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