Mechanism and mitigation of volumetric efficiency loss in a diaphragm compressor operated under negative suction pressure

Diaphragm compressors are widely used for their sealing reliability and ability to deliver high-purity gases, but their volumetric efficiency decreases sharply under negative suction pressure. This study reveals that the primary cause is air ingress into the inter-diaphragm gap, which induces diaphragm separation, limits the deformation of the gas-side diaphragm, and leads to substantial volumetric loss. To address this mechanism, an experimental system is established. In this setup, negative suction pressure is generated by throttling atmospheric air, and the inter-diaphragm gap is evacuated using a vacuum pump. Displacement sensors are employed to measure diaphragm deformation, and finite element analysis is performed to quantify losses from incomplete diaphragm motion at low pressures. The results show that without gap evacuation, volumetric efficiency decreases by 42%–82%, reducing compressor efficiency to below 20%. After evacuation, the maximum deformation of the gas-side diaphragm increases from 0.12 to 3.48 mm, and volumetric efficiency improves by 20%–60% within the suction pressure range of −0.25 to −0.05 bar. In addition, a volumetric-efficiency estimation model incorporating multiple loss mechanisms is developed and shows good agreement with the experimental data. The key contributions of this study are (i) identifying and experimentally verifying the air-ingress-induced diaphragm separation mechanism under negative suction pressure, (ii) demonstrating an effective mitigation by evacuating the inter-diaphragm gap with quantified performance gains, and (iii) developing and validating a volumetric-efficiency estimation model. These findings clarify the origin of volumetric loss under negative suction pressure and provide an effective approach to improve diaphragm compressor performance.