Fluid coming out of impeller has sufficiently high velocity and is converted to pressure using any or a combination of (i)diffuser (ii)spiral (also known as volute) casing. A diffuser is a diverging passage having a suitable angle of divergence so that separation of flow does not occur. Pressure loss at its entry is reduced by designing the entrance angle of the diffuser so that liquid coming from impeller enters into this passage smoothly. For this reason,