Hydrocyclones have been used at the industries to separate solids from liquids and sometimes to separate liquids from liquids by the difference in density between the fluid and the material to be separated in this equipment. The principle employed is centrifugal sedimentation, i.e., due to the fluid acquires a spiraling motion caused by the tangent feeding, the material of larger density is thrown against the wall of the hydrocyclone and dragged to the underflow while the one of smaller density proceeds for the overflow, forming a free vortex and a forced vortex to create the necessary force, the potential energy of process slurry is converted to kinetic energy at the cyclone feed inlet. The filtering hydrocyclone has another stream imposed of filtrate originating in the filtration in the conical area. Hydrocyclone use small physical space in comparison with flotation and gravity separators. Since there are no moving parts, cyclones are relatively maintenance-free. Hydrocyclones ( Deoiler hydrocyclones ) are used in the oil industry to remove oil from the produced water before the water is disposed overboard or reinjected into the formation.