. Applied thermodynamics for engineers. tons law, and by noting the temperature and pressure in the condenser, the pressureof the air, separately considered, may be computed. Then the volume of air, cal-culated as in Art. 236, must be reduced to the condenser temperature and pressure,and the pump made suitable for handling this volume (14). Commercial Types of Compressing Machinery 238. Classification of Compressors. Air compressors are classified accordingto the number of stages, the type of frame, the kind of valves, the method ofdriving, etc. Steam-driven compressors are usually mounted as
. Applied thermodynamics for engineers. tons law, and by noting the temperature and pressure in the condenser, the pressureof the air, separately considered, may be computed. Then the volume of air, cal-culated as in Art. 236, must be reduced to the condenser temperature and pressure,and the pump made suitable for handling this volume (14). Commercial Types of Compressing Machinery 238. Classification of Compressors. Air compressors are classified accordingto the number of stages, the type of frame, the kind of valves, the method ofdriving, etc. Steam-driven compressors are usually mounted as one unit with thesteam cylinders and a single common fly wheel. Regulation is usually effected byvarying the speed. The ordinary centrifugal governor on the steam cylinder im-poses a maximum speed limit; the shaft governor is controlled by the air pressure,which automatically changes the point of cut-off on the steam cyhnder. Power-driven compressors may be operated by electric motor, belt, water wheel, or in 134 APPLIED THERMODYNAMICS. TYPES OF COMPRESSOR 135 other ways. They are usually regulated by means of an unloading valve, whicheither keeps the suction valve closed during one or more strokes or allows the airto discharge into the atmosphere whenever the pipe lines are fully supplied. Inair lift practice, a constant speed is sometimes desired, irrespective of the the variable volume type of machine, the delivery of the compressor isvaried by closing the suction valve before the completion of the suction air in the cylinder then expands below atmospheric pressure. 239. Standard Forms. The ordinary small compressor is a single-stagemachine, with poppet air valves on the sides of the cylinder. The frame is of thefork pattern, with bored guides, or of the duplex type, with two single-stagecylinders. These machines maybe either steam or belt driven. The straightline compressors differ from the duplex in having all of the cylinders in onestraight line, regard
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