Abstract: The cylinder of professional setting is embodied in completely composite materials by wounding and demoulding. The composite material is porous and loose, which means it is essential to conduct research on their airtightness to prevent gas leakage in actual use and cause equipment failure. This paper mainly studies the detection method of cylinder sealability. Finally, a leak detection method was obtained by selecting different sealing methods, measurement method and error elimination methods. This method is to seal the out wall of the cylinder, fill the inner chamber with helium, and create a vacuum chamber inside the outer wall, where to use the helium mass spectrometer to detect the helium content. The method can effectively eliminate the interference of helium leakage from different sealing surfaces, which can also detect the airtightness of the cylinder without causing damage. Using this method, the cylinder leakage rate is on the order of 10^-10Pa·m³·s^-1 in a static environment.

Key words: composite material, airtightness, leakage rate