Air cushion surge chamber is a high performance device of water hammer protection and surge control. Its operation characteristics are important to long water distribution system. To operation simulation of air cushion surge chamber, polytropic equation method and rational heat transfer method are adopted presently. The former has not considered the heat transfer between gas and chamber wall. Though the latter considers this heat transfer, analysis of heat transfer type is improper. Gas characteristics of air cushion surge chamber in the processes of hydraulic transients in long distribution system are studied. This paper makes a deep analysis on rational heat transfer method in theory based on fundamental thermodynamic equations, and derives calculation equation of gas heat transfer with variable boundary through considering different air heat transfer types synthetically. Experiment is made in order to study on the polytropic exponent, more prefer value range of polytropic exponent is raised. So the new operation characteristics of air cushion surge chamber are obtained. Numerical calculation and model test results indicate that the new analysis method can simulate gas pressure variation more precisely in the process of hydraulic transients and ensure the safety of long water distribution system.

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