For instance, Neesse et al. realized the solids classification in submicron range, which cannot be achieved before, by using a 10 mm hydrocyclone operating at high feed pressure up to 6 MPa. They ob- served that operation at high feed pressures not only decreased cut size but also generated a high throughput, which was around 3 times higher than that obtained under normal pressure. This clearly demonstrated that, the smaller the cylindrical diameter, the larger the effects of feed pressure on separation performance.