Experiment and analysis were conducted to investigate the thermal expansion failure of the self-lubricated piston rings during the running of compressors. The cylinder of an existing compressor was modified and a combined piston was fabricated. The dynamic pressure distribution on each ring was measured during the running of the compressor. The process of the thermal expansion failure was simulated using the FEM software and the thermal expansion of the piston rings was observed with an observation hole in the cylinder. The results show that there were two kinds of the thermal expansion failure: when the cut was just closed

the unattached volume formed

yielding relatively balanceable pressure; when the temperature increased further

the interfaces of the cut would be stagger and the lateral face of the piston ring could not contact the lateral face of the piston ring groove

leading to the increase in the gas leakage. It is likely that bigger cut clearance should be employed to avoid the earlier thermal expansion failure.