Investigation of Fluid Load Redistribution and Diaphragm Mechanical Response Mechanisms in an Opposed Balance Pump

To address diaphragm stress concentration and poor delivery stability in conventional diaphragm pumps, this study investigates an opposed balance pump equipped with a radial balance device. A dynamic mesh technique based on user-defined function (UDF) was integrated with a fluid–structure interaction framework, a spring-based smoothing model, and a local remeshing criterion to synchronize computational-domain motion with diaphragm deformation under large-deformation conditions. Numerical simulations were combined with particle image velocimetry (PIV) measurements around the umbrella valve to experimentally characterize local velocity distributions and vortex evolution. Six operating conditions from 0.2Q to 1.2Q were examined to characterize the coupled evolution of diaphragm stress, total deformation, and internal flow. The results show that the maximum equivalent stress and total deformation vary nonlinearly with flow rate. The diaphragm exhibits the most favorable mechanical-to-fluid load ratio and the most stable response at 0.6Q–0.8Q. Symmetrical radial flow channels and the radial balance device regulate internal flow organization and facilitate fluid load redistribution by improving pressure uniformity and reducing asymmetric hydraulic loading, thereby decreasing both the maximum diaphragm stress and its fluctuation amplitude. Vortex evolution and pressure pulsation are identified as the primary hydrodynamic mechanisms causing alternating diaphragm loads. This study provides a theoretical basis for radial balance structure optimization, diaphragm load regulation, and the development of highly stable diaphragm pumping systems with improved hydraulic stability.