In this paper, equations of the one-dimensional, unsteady and compressible flow are transformed into characteristic equations to analyze the flow in a long pipe, and the characteristics of the pressure reduction in a long pipe is investigated numerically by the method of characteristics. The calculations are performed for pipes which have four kinds of bore, three lengths and five orifice ratios, and are compared with the experimental results. It was shown that the calculated results agree with the experimental results qualitatively well and that the characteristic method is available to analyze the flow in a long pipe.
