In the oil and gas industry, upstream and downstream hydrocyclones are used extensively to separate heavy or dense particles from the formation water/reservoir fluids. These hydrocyclones, after a long period of operation, can fail as a result of wear‐initiated leakage, thereby needing maintenance or replacement. A detailed investigation of this failure was carried out using computational fluid dynamics (CFD). One‐way and two‐way coupling of a discrete phase model was used along with the Reynolds stress turbulence model (RSM). Experimental studies were conducted to understand the flow dynamics within the hydrocyclone and to validate the computational model. Key findings, such as bifurcation of the inlet flow, local acceleration of fluid within the hydrocyclone, the impact of the sand drain pipe on fractional efficiency, and the impact of multiple particle sizes and density interactions on the degree of particle entrapment, are discussed in detail. The approach and results presented in this work provide useful insights and a systematic basis for improving the service life and separation efficiency of the hydrocyclone.