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On its way from the suction line into the compressor cylinder, or out of the cylinder into the discharge line, the gas encounters flow resistance not only in the valves but also in the valve pockets. These additional pressure drops are called pocket losses. Based on published laboratory measurements, these pocket losses can be quantified as long as flow areas in valves and valve pockets are constant. In reality, however, these flow areas are not constant but variable. This is easily understood in the case of a valve which opens, closes, and sometimes even flutters. With a pocket, this is less obvious, nevertheless its flow area may vary as a result of piston masking. With modern short stroke high speed compressors, it may happen that the piston masks the pocket during 80% of its stroke. This may have a considerable impact on pocket losses. But there is another flow problem: due to the high rotational speed, stroke is short and cylinder bore big. As the piston approaches its inner dead center position and cylinder volume is already small, the gas is squeezed out of it with a flow velocity which is considerable near the discharge valves, but zero on the side of the suction valves. This results in an asymmetric pressure distribution along the piston face which in turn causes the gas load to be eccentric. As a result, bending stresses are produced in the piston rod that may not be negligible. This paper deduces simple analytical models capable of giving reasonable estimate for both these adverse effects.
Your Price $195.00
List Price $195.00